# Comfort Ratio - How to read 5 to 10 pts differences?



## phboujon

Hi,

I am making a short list of blue water boats (for a potential purchase and sabbatical) by looking at their ratios, and one of the criteria my girlfriend and I are trying to understand is the comfort ratio.

While I understand how it is calculated, and what is the overall meaning, I have no clue (due to being an inexperienced sailor, still taking sailing classes) what 5 to 10 points difference really make once blue water sailing.

Case in point (from online database):

Tayana 37 - CR: 43.8 -> Reference point (RP)
Pacific Seacraft 37 - CR: 38.0 -> -5.8 of RP
Cabo Rico 36 - CR: 35.6 -> -8.2 of RP
Shannon 37 - CR:33.5 -> -10.3 of RP

My question isn't which boat is better, I am not there yet. What I'd like to understand is whether the differences between these boats, in term of motion comfort, can truly be perceived at sea? Is a Shannon 37 really less comfortable than a Tayana 37? Tayana 37 vs. PS 37? PS 37 vs. CR 36? etc... or am I paying too close attention to what is just a number?

None of the boats I am considering seems to be apart of more than 10-12 points on the comfort ratio. Should I be happy their comfort are in the 30-40 range and move on to care about other numbers / other issues?

Thank you for your help,

Cheers
Philippe


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## Delirious

> MCR = DISP / (.65*BEAM4/3(.7*LWL+.3*LOA)) This ratio was invented by Ted Brewer who say's he dreamed it up "tongue in cheek" as a measure of the motion comfort of a boat. A boat that has a more corky motion is considered less comfortable then one less affected by wave action. A higher value is better (if you like comfort). Smaller and beamier boats tend to have a lower ratio. This is best used to compare boats of similar size. A 26 footer should probably not be compared to a 40 footer using this ratio. The ratio is a factor of LOA and LWL and it may assume that boats with long overhangs tend to have wineglass shaped cross sections which provide more gradual buoyancy as they are immersed. However, a boat like a Valiant 42 has a long LWL for it's LOA and possesses this more wineglass shaped cross section. The ratio also favors displacement (higher gives larger result) and there is no accounting for distribution of weight. It also takes no account of waterline beam, a value that can be quite informative but is rarely available on stat sheets.


My interpretation is it relates how "corky" a sailboat feels, based on ratio of overhangs to waterline. But it does not take into account how "cow-like" or sluggish a non-corky boat can feel. My own boat only rates a 24.0, but I have no open ocean plans.

Based on these measurements the sailboats of the 60's through 80's will have a great advantage over those designed in the last 20 years with the more "European" hull shapes (beamy with lwl = loa). And maybe that is so.


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## Valiente

Keep in mind that any center cockpit or pilothouse boat is likely to be more comfortable by virtue of the fact that you are not at one end of a boat that is moving like a slow see-saw through the waves.

Comfort is best appreciated on the boats themselves. I have found that I don't notice the "snappy" motion of a race boat if I am having fun on a race, just as I don't resent the stately tack of a heavy displacement full-keeler.

I certainly notice a change in motion, however, when I go up from the pilothouse of that full keeler onto the aft deck and the "outside helm".


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## RainDog

According to the formula by Delerious, the comfort ration is based on three values: LOA, LWL, DISP, and BEAM. The four boat you list are very close in LOA and Beam. That means the main cause of the different values are Displacement and LWL. All else being equal, a boat with a higher displacement is slower, but has a better motion. All else being equal, a boat with a shorter water line is slower. I think the better motion in this case is probably more controversial. 

In any case, all of these are quite heavy boats that have moderate numbers in other areas. They will all be comfortable. I would focus far less on the motion comfort ratio than other factors when comparing these boats. Other factors that I think are more important when comparing these four boats are build quality and function of deck, cockpit, and cabin layout (you will have to tour all four do decide this). 

Even more important: which of these boats makes your heart sing when you look at it? They are all great boats, but the one that takes your breath away is the right one for you.


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## phboujon

Thanks all for the answers. I appreciate it. 

I'll definitely ask more information when I am further in my research (and reading) of boats. For now, the cruising plan is still very fuzzy, just at the beginning, when dreams tend to be bigger than reality 

Cheers
Philippe


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## Jeff_H

5 to 50 points difference is totally useless in telling you about a boat characteristics. Its seems that as soon as someone posts a question about the seaworthiness of some particular boat, that a well meaning responder sends them to Carl's Sail Calculator to look at the Capsize Screen Formula and the Motion Comfort Index. And no sooner than poster questions the seaworthiness of some boat, that someone cites the Capsize Screen Formula and the Motion Comfort Index in that vessel's defense or prosecution. But as I have explained many times in the past, (and I am about to explain yet again) these surrogate formulas tell almost nothing about how the reality of a boat's likelihood of capsize or its motion comfort. In fact they provide so little indication of a boat's behavior that to rely on them in any way borders on the dangerous. 
<O</O

Both of these formulas were developed at a time when boats were a lot more similar to each other than they are today. These formulas have limited utility in comparing boats other than those which are very similar in weight and buoyancy distribution to each other. Neither formula contains almost any of the real factors that control motion comfort, the likelihood of capsize, or seaworthiness. Neither formula contains such factors as the vertical center of gravity or buoyancy, neither contains weight or buoyancy distribution (of the hull both below and above the waterline), the extent to which the beam of the boat is carried fore and aft, and neither contains any data on dampening, all of which really are the major factors that control motion comfort or the likelihood of capsize. <O</O
<O</O

I typically give this example to explain just how useless and dangerously misleading these formulas can be. If we had two boats that were virtually identical except that one had a 500 pound weight at the top of the mast. (Yes, I know that no one would install a 500 lb weight at the top of the mast.) The boat with the weight up its mast would appear to be less prone to capsize under the capsize screen formula, and would appear to be more comfortable under the Motion Comfort ratio. Nothing would be further than the truth. <O</O
<O</O

And while this example would clearly appear to be so extreme as to be worthy of dismissal, in reality, if you had two boats, one with a very heavy interior, shoal draft, its beam carried towards the ends of the boat near the deck line, a heavy deck and cabin structure, perhaps with traditional teak decks and bulwarks, a very heavy rig, heavy deck hardware, a hard bottomed dingy stored on its cabin top, and the resultant comparatively small ballast ratio made up of low density ballast. And if we compare that to a boat that is lighter overall, but it has a deep draft keel, with a higher ballast ratio, the bulk of the ballast carried in a bulb, its maximum beam carried to a single point in the deck so that there was less deck area near the maximum beam, a lighter weight hull, deck and interior as well as a lighter, but taller rig, it would be easy to see that the second boat would potentially have less of a likelihood of being capsized, and it is likely that the second boat would roll and pitch through a smaller angle, and would probably have better dampening and so roll and pitch at a similar rate to the heavier boat, in other words offer a better motion comfort....And yet, under the Capsize Screen Formula and the Motion Comfort Index it would appear that the first boat would be less prone to capsize and have a better motion when obviously this would not be the case.<O</O
<O</O

There are some better indicators of a vessel's likelihood of capsize. The EU developed their own stability index called STIX, a series of formulas which considered a wide range of factors and provides a reasonable sense of how a boat might perform in extreme conditions. Unfortunately meaningful results require a lot more information than most folks have access to for any specific design. The Offshore Committee of US Sailing developed the following simplified formula for estimating the Angle of Vanishing Stability (Sometimes referred to as the 'AVS', 'limit of positive stability', 'LPS', or 'Latent Stability Angle' ):<O</O
_Screening Stability Value ( SSV ) = ( Beam 2 ) / ( BR * HD * DV 1/3 )_<O</O
_Where; <O</O_
_BR: Ballast Ratio ( Keel Weight / Total Weight )_<O</O
_HD: ffice:smarttags" />lace w:st="on">Hull</ST1lace> Draft _<O</O
_DV: The Displacement Volume in cubic meters. DV is entered as pounds of displacement on the webpage and converted to cubic meters by the formula: _<O</O
_Displacement Volume in Cubic Meters = ( Weight in Pounds / 64 )*0.0283168_<O</O
_The Beam and <?xml:namespace prefix = st1 ns = "urn:schemas-microsoft-com







<ST1







<ST1lace w:st="on">Hull</ST1lace></st1:City> Draft in this formula are in meters. These values are entered in feet on the webpage and are converted to meters before SSV calculation._<O</O
_Angle of Vanishing Stability approximately equals 110 + ( 400 / (SSV-10) )_<O</O
<O</O

There is a convenient calculator at http://www.sailingusa.info/cal__avs.htm<O</O
<O</O

It should be noted that the AVS is only one indicator in evaluating the likelihood of capsize, meaning it only predicts the point at which the vessel wants to turn turtle. It does not predict the amount of force that would be required to heel the vessel to that limit, nor does it predict how the shape of the boat might encourage wave action to roll the boat closer to the angle at which it no longer wants to return. <O</O
<O</O
<O</O


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## sailingdog

LOL...Hey Jeff, you do know you're replying to a thread from last summer, right??


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## Jeff_H

Yes I was aware of that. I had seen Phillipe's post about boats not to take voyaging and in forming an answer I had taken a couple minites to look at his earlier posts trying to see if I could get a sense of where he was coming from and how experienced he was since his short list and criteria were so strange. 

At the time I noticed this thread and thought I would return to it rather than highjack his other post when he had specifically said that he did not want to discuss his criteria on that post. Since he had posted the other thread I figured he was actively on the board and so might see this. 

Jeff


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## JohnRPollard

Something very odd happened above. At least, on my screen anyway. 

I see Jeff's post #8, with Sailingdog's signature line at the bottom of his post. Then in post # 9, Jeff appears to be replying to a post (by SD?) that doesn't show up on my screen. Anyone else seeing this?


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## christyleigh

JohnRPollard said:


> Something very odd happened above. At least, on my screen anyway.
> 
> I see Jeff's post #8, with Sailingdog's signature line at the bottom of his post. Then in post # 9, Jeff appears to be replying to a post (by SD?) that doesn't show up on my screen. Anyone else seeing this?


 You must have slipped in between the cracks in the posts/web/universe because now I'm seeing normal stuff and in fact your post is #9 Time warp........................  Danger ...... Danger........... :laugher


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## blt2ski

John,

It appears to be on you screen only,

I also agree Jeff should make the comment her for the OP per there most recent post of about 24 hrs ago, with a BIG list or eclectic boats.

marty


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## JohnRPollard

Wow, something's really messed up on my end, then. Now the posts are numbered differently, and it even skips 2 post #s. I don't see SD's post at all, only his signature tagged on to the end of Jeff's post about the CR ratio.

Are you guys all seeing SD's post, then?


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## JomsViking

John,

SD's posts looks fine, but I see none of yours 



JohnRPollard said:


> Wow, something's really messed up on my end, then. Now the posts are numbered differently, and it even skips 2 post #s. I don't see SD's post at all, only his signature tagged on to the end of Jeff's post about the CR ratio.
> 
> Are you guys all seeing SD's post, then?


Sorry, couldn't resist - it looks fine here.  
Q: Should we have a sticky "Carls Sail Calculator should only be used to compare vessels otherwise comparable to Pinta and Nina" or whatever?


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## sailingdog

It's all in your head...



JohnRPollard said:


> Something very odd happened above. At least, on my screen anyway.
> 
> I see Jeff's post #8, with Sailingdog's signature line at the bottom of his post. Then in post # 9, Jeff appears to be replying to a post (by SD?) that doesn't show up on my screen. Anyone else seeing this?


Jeff-

Thanks for the clarification.


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## SW329xl

JohnRPollard said:


> Something very odd happened above. At least, on my screen anyway.
> 
> I see Jeff's post #8, with Sailingdog's signature line at the bottom of his post. Then in post # 9, Jeff appears to be replying to a post (by SD?) that doesn't show up on my screen. Anyone else seeing this?


Check with another moderator. The site is going to treat mods and non-mods differently. Could be a mod specific bug. Also might want to check with the SAs (Sys admins, not the other site) to see if there was any maintenance or upgrades performed. They may have broken something trying to give you greater superpowers. And of course try clearing your cache, closing your browser, and trying again.


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## JohnRPollard

Bizarre. This is what I see:



> 5 to 50 points difference is totally useless in telling you about a boat characteristics. Its seems that as soon as someone posts a question about the seaworthiness of some particular boat, that a well meaning responder sends them to Carl's Sail Calculator to look at the Capsize Screen Formula and the Motion Comfort Index. And no sooner than poster questions the seaworthiness of some boat, that someone cites the Capsize Screen Formula and the Motion Comfort Index in that vessel's defense or prosecution. But as I have explained many times in the past, (and I am about to explain yet again) these surrogate formulas tell almost nothing about how the reality of a boat's likelihood of capsize or its motion comfort. In fact they provide so little indication of a boat's behavior that to rely on them in any way borders on the dangerous.
> 
> Both of these formulas were developed at a time when boats were a lot more similar to each other than they are today. These formulas have limited utility in comparing boats other than those which are very similar in weight and buoyancy distribution to each other. Neither formula contains almost any of the real factors that control motion comfort, the likelihood of capsize, or seaworthiness. Neither formula contains such factors as the vertical center of gravity or buoyancy, neither contains weight or buoyancy distribution (of the hull both below and above the waterline), the extent to which the beam of the boat is carried fore and aft, and neither contains any data on dampening, all of which really are the major factors that control motion comfort or the likelihood of capsize.
> 
> I typically give this example to explain just how useless and dangerously misleading these formulas can be. If we had two boats that were virtually identical except that one had a 500 pound weight at the top of the mast. (Yes, I know that no one would install a 500 lb weight at the top of the mast.) The boat with the weight up its mast would appear to be less prone to capsize under the capsize screen formula, and would appear to be more comfortable under the Motion Comfort ratio. Nothing would be further than the truth.
> 
> And while this example would clearly appear to be so extreme as to be worthy of dismissal, in reality, if you had two boats, one with a very heavy interior, shoal draft, its beam carried towards the ends of the boat near the deck line, a heavy deck and cabin structure, perhaps with traditional teak decks and bulwarks, a very heavy rig, heavy deck hardware, a hard bottomed dingy stored on its cabin top, and the resultant comparatively small ballast ratio made up of low density ballast. And if we compare that to a boat that is lighter overall, but it has a deep draft keel, with a higher ballast ratio, the bulk of the ballast carried in a bulb, its maximum beam carried to a single point in the deck so that there was less deck area near the maximum beam, a lighter weight hull, deck and interior as well as a lighter, but taller rig, it would be easy to see that the second boat would potentially have less of a likelihood of being capsized, and it is likely that the second boat would roll and pitch through a smaller angle, and would probably have better dampening and so roll and pitch at a similar rate to the heavier boat, in other words offer a better motion comfort....And yet, under the Capsize Screen Formula and the Motion Comfort Index it would appear that the first boat would be less prone to capsize and have a better motion when obviously this would not be the case.
> 
> There are some better indicators of a vessel's likelihood of capsize. The EU developed their own stability index called STIX, a series of formulas which considered a wide range of factors and provides a reasonable sense of how a boat might perform in extreme conditions. Unfortunately meaningful results require a lot more information than most folks have access to for any specific design. The Offshore Committee of US Sailing developed the following simplified formula for estimating the Angle of Vanishing Stability (Sometimes referred to as the 'AVS', 'limit of positive stability', 'LPS', or 'Latent Stability Angle' ):
> Screening Stability Value ( SSV ) = ( Beam 2 ) / ( BR * HD * DV 1/3 )
> Where;
> BR: Ballast Ratio ( Keel Weight / Total Weight )
> HD: ffice:smarttags" />lace w:st="on">Hulllace> Draft
> DV: The Displacement Volume in cubic meters. DV is entered as pounds of displacement on the webpage and converted to cubic meters by the formula:
> Displacement Volume in Cubic Meters = ( Weight in Pounds / 64 )*0.0283168
> The Beam and
> Telstar 28
> New England
> 
> You know what the first rule of sailing is? ...Love. You can learn all the math in the 'verse, but you take
> a boat to the sea you don't love, she'll shake you off just as sure as the turning of the worlds. Love keeps
> her going when she oughta fall down, tells you she's hurting 'fore she keens. Makes her a home.
> 
> -Cpt. Mal Reynolds, Serenity (edited)
> 
> If you're new to the Sailnet Forums... please read this POST.
> 
> Still-DON'T READ THAT POST AGAIN.


But when I press the "quote" button, this is what I get:



sailingdog said:


> LOL...Hey Jeff, you do know you're replying to a thread from last summer, right??


But that quote of Sd above is not otherwise visible.

Something's obviously messed up on my end. Sorry about the distraction...


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## smackdaddy

JohnRPollard said:


> Wow, something's really messed up on my end, then. Now the posts are numbered differently, and it even skips 2 post #s. I don't see SD's post at all, only his signature tagged on to the end of Jeff's post about the CR ratio.
> 
> Are you guys all seeing SD's post, then?


Actually, I got the same thing a while back when quoting GeorgeB. It's like the post was somehow left open and stuff was appended to it. Bugginess.

Do you know how much I'd give not to see SD's posts? Heh-heh.


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## phboujon

Jeff, thanks for the reply. Since that post, I have been reading a lot more.

The purpose of this Jun 09 post was for me to understand whether a Shannon 37 was really less comfortable at sea (in term of motion) than a Tayana 37, and to get a feeling from users of this forum who own or sail those boats how the boats feel.

I'd love to have the time to go sailing on every one of those boats, but I don't. Therefore, while I agree formulas cannot tell you exactly how a boat will behave, formulas are of a help to weed out the thousands of boats that exist out there to a short list that one can be comfortable with because they have 'on paper' good characteristics. The next step then being to visit those boats on the short list, and sail them hopefully.

I am working still on the short list, as my other post shows, but I am starting as well to visit those boats.

Thanks
Philippe


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## JomsViking

Philippe,
But you have to realize that you will potentially rule out a lot of great boats because of a flawed formula, and vice versa.

/Joms


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## kevlarpirate

*Physics rules , not opinion*

Jeff says:

"I typically give this example to explain just how useless and dangerously misleading these formulas can be. If we had two boats that were virtually identical except that one had a 500 pound weight at the top of the mast. (Yes, I know that no one would install a 500 lb weight at the top of the mast.) The boat with the weight up its mast would appear to be less prone to capsize under the capsize screen formula, and would appear to be more comfortable under the Motion Comfort ratio. Nothing would be further than the truth "

Kevlar Pirate says:

Actually, 500 lbs at the top of the mast would prevent a rollover
why ? because there is a dynamic world out there not just a static world.

In practice we would never do this for other reasons however the mass 
of the mast is important 
This is why a boat which loses it's mast is more susceptible to rollover
even though the center of gravity is lower
Jeff, I would suggest you take a class on statics and dynamics, 
read up on moment of inertia it goes by radius squared 
respectfully, you are out of your field.

The comfort motion formulas and capsize ratio formulas are still
very valuable. I am not defending them to the letter, however there is no
designs today or ever which can invalidate these basic formulas in spirit.

CSR did not intend for someone to denigrate it by using some far out example 
as you have attempted here with your 500 lb weight.
Instead of misleading readers , you may want to first qualify your statement by admitting your own boat does not do too well with these formulas.

calculus and Newtonian physics have accurately served this world for 400 years 
these formulas are plenty acceptable for the purpose they were developed


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## PCP

kevlarpirate said:


> Jeff says:
> 
> "I typically give this example to explain just how useless and dangerously misleading these formulas can be. If we had two boats that were virtually identical except that one had a 500 pound weight at the top of the mast. (Yes, I know that no one would install a 500 lb weight at the top of the mast.) The boat with the weight up its mast would appear to be less prone to capsize under the capsize screen formula, and would appear to be more comfortable under the Motion Comfort ratio. Nothing would be further than the truth "
> 
> Kevlar Pirate says:
> 
> Actually, 500 lbs at the top of the mast would prevent a rollover
> why ? because there is a dynamic world out there not just a static world.
> ....
> Jeff, I would suggest you take a class on statics and dynamics,
> read up on moment of inertia it goes by radius squared
> respectfully, you are out of your field.
> 
> The comfort motion formulas and capsize ratio formulas are still
> very valuable. I am not defending them to the letter, however there is no
> designs today or ever which can invalidate these basic formulas in spirit.
> 
> CSR did not intend for someone to denigrate it by using some far out example
> as you have attempted here with your 500 lb weight.
> Instead of misleading readers , you may want to first qualify your statement by admitting your own boat does not do too well with these formulas.
> 
> calculus and Newtonian physics have accurately served this world for 400 years
> these formulas are plenty acceptable for the purpose they were developed


I don't understand what you are talking about .

If we put 500 lb on top of a mast, considering its height (that works as a giant arm), for maintaining the same stability curve we would have to add something like to 3700 lb to the Ballast.

Or put it another way: How would you think the Tayana 37 would perform if we took away 3700 lb of its Ballast (that's almost half of it)?

Well, better not put any sails on that boat, because it is going to be a very unstable boat

Regards

Paulo


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## Paul_L

phboujon said:


> Jeff, thanks for the reply. Since that post, I have been reading a lot more.
> 
> The purpose of this Jun 09 post was for me to understand whether a Shannon 37 was really less comfortable at sea (in term of motion) than a Tayana 37, and to get a feeling from users of this forum who own or sail those boats how the boats feel.
> 
> I'd love to have the time to go sailing on every one of those boats, but I don't. Therefore, while I agree formulas cannot tell you exactly how a boat will behave, formulas are of a help to weed out the thousands of boats that exist out there to a short list that one can be comfortable with because they have 'on paper' good characteristics. The next step then being to visit those boats on the short list, and sail them hopefully.
> 
> I am working still on the short list, as my other post shows, but I am starting as well to visit those boats.
> 
> Thanks
> Philippe


Philippe,
Some formulas are helpful in comparing boats that are similar enough, others just don't add much value. I don't think Motion Comfort adds much of anything. I have a fair amount of experience on two boats that I've owned. They are both close in overall length. One has MC of 36, the other 21. I suffer from seasickness pretty easily and need to really watch myself offshore. I can unquestionably tell you that for me, the offshore comfort of the boat with the MC 21 is much better than the 36, even in rough conditions.

Paul L


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## kevlarpirate

yes of course it would change the statics and the boat would likely lay over considerably to some heel angle and stay there ( in a calm lake) 
my point is that jeff is dismissing the value of the behavior in the dynamic world.  He rambles about interior weight etc, and center of gravity being too high. 

In practice however, his argument can be null and voided by one experiment and that is by removing the mast , thus, even though substantially lowering the CG, now in the dynamic world of a high beam sea, the loss of moment of inertia is more dominant in affecting the behavior and now the boat is more prone to roll over. 

Here is a link to a huge argument which erupted a couple of years ago where jeff dismissed the work of some very good naval architects and authors.
I am amazed he continues to argue this point.


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## kevlarpirate

*Capsize ratio*

Capsize ratio - Cruisers & Sailing Forums

I can mention here that I race and run races , that I have raced about 50 boats back to 1971 or so and remember them all. The light weight boats, I don't care how fast , will always get kicked around and the motion comfort will 
be an issue. I own 2 early 70's ex SORC racers and I wouldn't trade them for 
boats costing way more , they are battlewagons , go upwind 
without pounding and are very comfortable and stable and QUIET 
at anchor. there is way more to cruising than going fast off the wind


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## PCP

You are talking about the importance and suitability of two different old screening formulas, the motion comfort and the capsize ratio formula.

About stability and capsizing you say:



kevlarpirate said:


> Actually, 500 lbs at the top of the mast would prevent a rollover.
> why ? because there is a dynamic world out there not just a static world. .....Jeff, I would suggest you take a class on statics and dynamics, &#8230;respectfully, you are out of your field.


As I have explained, to maintain the same stability curve and AVS (talking about a tayana 37), for compensating that weight on top of the mast you would have to add almost 3700lbs to the ballast of that boat. That means that the boat, with the 500lbs on top of the mast would be a lot less stable, would be unsafe and would have a very lower AVS point (point of no return).

Saying that adding "500lbs on top of the mast would prevent a rollover" is a complete nonsense and it shows that you don't know of what you are talking about.

From someone that shows such an improper theoretical comprehension of a boat stability ( I believe that almost all sailors will intuitively understand clearly that a weight of 500lbs on the top of their the mast will reduce drastically the boat stability), suggesting that Jeff, an informed member of this forum that gives himself the trouble to post about more technical stuff, needs to take classes on statics and dynamics is ridiculous but, above all, sad.

You have said:


kevlarpirate said:


> Here is a link to a huge argument which erupted a couple of years ago where jeff dismissed the work of some very good naval architects and authors. I am amazed he continues to argue this point.


I was curious and I had a look. The Architect is John Rousmaniere and it was jeff that had asked his opinion about the capsizing formula. Rousmaniere says:

"&#8230;Now, *too many people try to make way too much of it*. Note that in ANNAPOLIS I carefully use the words "simple," "estimate," "and "guideline." *This is NOT a measure of stability range (the best gauge, which any reputable boatbuilder and designer will provide)*. It is NOT a test of ultimate seaworthiness. It IS a simple test that (to quote its creators of 20 years ago, Dick McCurdy and Karl Kirkman) offers "a general indication of a boat survivability using only data that comes readily to hand." 
&#8230;&#8230;
*Again, the ultimate test is stability range, which is based on many technical factors*&#8230;..

*What does the screening test take into account*? First,* beam*. Wide beam means low range of stability. A wide boat will flip earlier and also stay turtled longer than a narrow boat. Second, *displacement*. Heavier boats have a greater moment of inertia than light ones, so are harder to flip. What the screening test does is provide a number that assists in making a comparison, which I think is extremely helpful".
(bolds are mine)

And JOHN ROUSMANIERE finishes with flattering words towards Jeff. He asks Jeff: "You follow this pretty thoroughly. Do you work in a design office?"

But the useful comparison Rousmaniere is talking about it is only valid if you compare similar boats, I mean, boats with the same type of design.

As Jeff have said and and as you can see by the JOHN ROUSMANIERE answer, the formula does not take into account the position of ballast and therefore the boat center of gravity. On a same hull, if we put the same ballast on a bulb at the end of a 5M fin Keel, or all distributed along a long keel with a max draft of 1,6M, we will obtain, using that formula, the same stability number. That means that the same hull, with the two different keel and ballast configurations will have the same stability range. Of course that is obviously very untrue.

It is well known that an Open60, that is a beamy boat with a big draft and a bulb, has a huge positive stability and also an inexistent inverted stability. If we apply that old formula to these kinds of boats (that have all ballast deep down on a bulb) we will obtain a boat with a very poor stability, an easy to capsize boat and an unsafe boat for offshore work. &#8230;and that is ridiculous&#8230; these are, for their size, among the more stable, hard to capsize and seaworthy boats.

Regarding comfort ratio it is worth to hear its creator, Ted Brewer:

"COMFORT RATIO (CR): ...*does provide a reasonable comparison between yachts of similar type*. ...The intention is to provide a means to* compare **the motion comfort of vessels of similar type and size&#8230;.*

*...Do consider, though, that a sailing yacht heeled ... will have a much steadier motion than one bobbing up and down ..*

Nor will one human stomach keep down what another stomach will handle with relish, or with mustard and pickles for that matter! 

*It is all relative*."

(bolds are mine)

The tastes of different sailors about the kind of sea motion they prefer, varies a lot. What is comfortable to you can be just boring and devoid of any sailing pleasure to another cruising sailor.

The type of comfort motion you like is a very personal thing, and varies as much as the different kind of cruising boats that are suitable to do Ocean passages, from the relatively heavy boats that you favor to the fast cruising racers, or Open type boats.

I have owned a heavy displacement boat and I have owned a light displacement boat. I do prefer the motion of the light boat, not in all situations but on almost all of them. You have seen that on this thread I am not the only one that thinks that way. That doesn't mean I am right. There is not right or wrong here. Sailors should try both kinds of boats to see the difference in type of motion and to make a personal choice.

Regards

Paulo

[/font]


----------



## kevlarpirate

1 As I said of course 500 lbs would reduce the ultimate STATIC
stability curve..... Are you are taking my statement out of the spirit it was intended ? I was using that to differentiate between statics and dynamics
only and thought any reader would see for that specific reason. 

2 the screening formulas are not old , unless in your head Newtonian physics is 'old"

3 we can easily prove the roll moment of inertia is DOMINANT over CG by removing the mast thereby increasing roll over frequency in a big sea even though the CG is much lower .... need I say this the 3rd time?

IMO ,the author did not by any means compliment jeff for his understanding of this formula, following it, is not understanding it and being objective 

The author stated that these formulas were an estimation of a boats behavior in a violent sea and was not a prediction.

An estimation is not absolute, but it is valid for MOST cases.
Most people posting here are not sailing open 60's, they are sailing production boats which these formulas are quite adequate.

I would also suggest you pull up some static stability curves of boats which 
do well under these "old" formulas and boats which do poorly under this "old" formula and you will see a strong correlation. That is my simple point.

I believe the author understands these formulas are quite unpopular to 
many boat owners and manufacturers whose boats do not show good numbers. This is a different subject entirely and enters into defensive and emotional territory. 

I say that's just too bad, formula is valid and can be proven adequate
many more times than not 

I have been in physics professionally all my adult life.. These concepts are quite basic, you do not have to be a naval architect to understand them.
but you do have to have an understanding of Statics and Dynamics

Any attempt to denigrate well done work like these formulas because of one or two examples and then try to apply those very few cases to speak for the entire lot only proves bias.

That is exactly what is happening here. with jeff's and your own views.
I can say further that jeff shows an amazing arrogance to denigrate 
the works of someone in the business for so long and then contact that same author at a later date...

And for what reason? so the author would retract his work? say he was wrong ? The author did nothing of the kind, he continues to defend it 
as he should .. Why? because the formulas stand valid.

Incidentally, very deep bulbs cause other problems, like getting slammed down in a trough on its beam, and that is a different subject in itself
we can talk about if you care to go to the next level


----------



## Barquito

So, would it be reasonable to say that in comparing boats (on paper) it is way more important to understand the characteristics that will tend to make the boat behave in certain ways (heel, roll...) than it is to cram those stats into a formula?


----------



## PCP

Barquito said:


> So, would it be reasonable to say that in comparing boats (on paper) it is way more important to understand the characteristics that will tend to make the boat behave in certain ways (heel, roll...) than it is to cram those stats into a formula?


Kevlarpirate I have waited a long time for you to answer Barquito. I am curious.
But as it seems that you are not going to answer, perhaps I can at least answer to this:


kevlarpirate said:


> ...
> 3 we can easily prove the roll moment of inertia is DOMINANT over CG by removing the mast thereby increasing roll over frequency in a big sea even though the CG is much lower .... need I say this the 3rd time?..


The main reason that makes a sailboat without mast more vulnerable to capsize is because a sailboat without a mast is not sailing anymore. On storms capable of generating breaking waves capable of capsizing oceangoing sailboats you will have winds over 50k. I have seen sailboats doing on those conditions, more than 10k on bare pools. Even without sails the boats are sailing, and not bouncing around, like a boat without a mast.

Basically it is the same reason that will make a motor boat easy to capsize in bad weather if he is dead on the water. The same motorboat, under a powerful engine will be many times safer and difficult to capsize.

I don't see any meaning on that story of the domination from the roll moment of inertia over the CG. Firstly because the CG is not a force. To find the relevant force (Righting moment) you will need to multiply the GZ ( righting arm) by the boat displacement. The CG is only relevant to find the GZ (the GZ is the horizontal distance between the CB (center of buoyancy) and CG (vertical center of gravity).

Then you need to find the energy needed to capsize the boat and for that you have to add all righting moments at all points of heel, from 1 degree to the AVS point (the area under the positive part of the RM curve).

Roll moment of inertia is only important if the boat mass is comparable or bigger than the breaking wave mass. That's the case with a ship, not with a typical sailing boat. The mass of a breaking wave will overcome the mass of a sailboat, so the roll moment of inertia is going to be easily overcome by the wave mass and when the boat starts to roll a torque is created (moment of force) that will tend to carry that rotating movement forever. The force that will oppose that moment and that (hopefully will stop it) is the Righting moment (RM).

The righting moment curve, the one that shows all righting moments at all points of heel, the one that can represent the total energy to capsize the boat is the one that Archt. John Rousmaniere says that is "the best gauge , which any reputable boatbuilder and designer will provide" as opposing to "his" Capsizing formula "that is NOT a measure of stability range" just a "guideline".

I believe this is a bit too much theoretical for many of the members, so I will post a comparison between several RM curves of boats of different sizes. The areas behind the positive parts of the curves represents the energy needed to capsize each boat. The point where the curve crosses for the negative part is the AVS point (point of no return). The area over the negative part of curve represents the energy needed to return a capsized boat to its original position.










Regards

Paulo


----------



## kevlarpirate

I did not answer barquitos question because it was vague and open ended, perhaps I should have engaged him more.

I mentioned I use physics regularly in my business, I had Statics and Dynamics , and all the math and physics classes for an engineering degree many years ago and that these laws of Newtonian physics serve our everyday lives. 

Without arguing your statements I will try to illustrate with an example :
Suppose you were sailing along on a reach or just sitting bare poles fishing for that matter, and you looked to the side and see a 30 foot breaking wave approaching 
and you have one wish to be granted.

Here would be what you should wish for : That for one instant in time , say for 5 seconds , that out of heaven , a 50 pound sandbag would be attached to the top of your mast , a second before the wave hit . and after the wave past that same sandbag would be removed. Actually , a 500 lb sandbag would be way better in this case. 

What this illustrates is moment of inertia which will resist your boat being rolled.
The wave would sweep through you , not roll you over. 
The more mass up there, the more energy is needed to put your boat into motion. 
Moment of inertia goes by radius squared

Also worth mentioning here is your statement about the powerboat . 
To that statement, a boat which has no forward motion will lie ahull and therefore become more vulnerable to a roll. As a related note a boat going fast will 
exhibit Newton’s first law and therefore you are thinking in the dynamic world , not the static world. 

I will also mention the capsize screening ratio is not invalidated because it does not take into account the specific height of CG. We all know we don’t carry our keels on deck. CSR is valid because all the common boats we speak of , including the 
Sport boats of today still have ratios very close to each other. 

The behavior of a boat in the real world is described by both the static AND dynamic inputs. 

A last note , I am not here to give physics lessons, this knowledge is in the books
Which I have in my library for decades, I am posting for the purpose of countering 
misinformation and in some cases disinformation, not yours by the way, however 
I cannot stress enough the importance of a rigorous understanding of moment of inertia and the relationship between statics and dynamics /Kev


----------



## kevlarpirate

one more thing PCP , don't get the impression I am a physics teacher sticking my toe in the world of sailing . I am a 40 year veteran of ocean racing 
and have the additional blessing of being able to understand the physics

I am happy to answer to any and all issues you care to engage /Kev


----------



## kevlarpirate

Paulo 

it has been some days now. I assume you are reading up on statics and dynamics, along with watching the races. Would you like to talk more? 

By the way , the static curves you posted show the dangers of "marketing" 
influence. The boats you show (new designs) except for one ,have dreadful curves

Buyers apparently don't pay much attention to this. You state that this theoretical stuff should be left alone because it's over the head of most of the board readers here. Interesting to me is this board should represent more
intelligent sailors than most. So if your statement is correct , this is really a sad state of affairs.

I personally own two large early 70's IOR boats and their curves are far superior, each with over 130 degrees and over a 7:1 ratio of positive vs neg stability area under the curve.

Early IMS boats like the J35 when fat butts , zero deadrise and low ballast numbers started to emerge actually had curves as bad as the worst of early 80's IOR curves. 

What should we conclude from all this? 

You and I obviously did not get off on a good footing 

I wish sailaway21 would come back here 
He is very well versed at this and you may want to read his posts if you have a continued problem with mine 

also he recommended a book "Stability and Trim for the Ship's Officer"
and offered up a very well put together and unbiased account of these issues.


----------



## PCP

kevlarpirate said:


> .....By the way , the static curves you posted show the dangers of "marketing"
> influence. The boats you show (new designs) except for one ,have dreadful curves
> 
> Buyers apparently don't pay much attention to this......
> I personally own two large early 70's IOR boats and their curves are far superior, each with over 130 degrees and over a 7:1 ratio of positive vs neg stability area under the curve.
> 
> Early IMS boats like the J35 when fat butts , zero deadrise and low ballast numbers started to emerge actually had curves as bad as the worst of early 80's IOR curves.
> 
> What should we conclude from all this?
> 
> You and I obviously did not get off on a good footing
> 
> ....


Ok, easy to talk, harder to show

Post those curves of old boats that are "far superior" and we can talk and see about that.

Regards

Paulo


----------



## kevlarpirate

Not hard at all, My Performance Package is on board , I can scan it 
or take dig photos and send as jpeg i guess.
It is not a massaged curve either like some do in hopes of getting a 
category 0 or 1.

I will also post a curve of a J-35 which has a pos to neg of 1.5 
BTW the expression is area "under" the curve no matter if the portion of the curve is in positive or below zero in negative territory 

I will need a day or so, will see the boats tomorrow, so in the meanwhile , why don't yo do some reading since now I am working for you here . then we can amp it up a bit , if you like. 

I am not biased or old school by the way, I am dedicated to physics, safe designs, I am current on process and manufacturing technology , ,uncompromising and I have a almost total disregard for marketing hype
and personal bias and defending compromise

Kev


----------



## PCP

kevlarpirate said:


> ...BTW the expression is area "under" the curve no matter if the portion of the curve is in positive or below zero in negative territory
> .....
> Kev


Please, explain what you mean with this statment.

Regards

Paulo


----------



## kevlarpirate

Paulo , it's just math talk

in this case , the curve looks like a distorted sine wave. If you take a function such as that and use calculus, you can determine the area under the curve by integrating . If that were say an electrical current flowing , we would refer to that area as the energy under the curve. Once the curve goes negative it is still energy, the sum of the two as the total energy even though one part is in negative territory , (below zero) and so we just think of it as the absolute value , meaning it has no sign (positive or negative) 

I mention current flowing as an electrical analog, it may help, but back to boats
the static curve shown shows the moment arm or torque as a function of heel angle. It should be noted that the smaller boat shows less moment arm 
on the Y axis. But look, it is only a 4.3 ton boat, so therefore it cannot develop the level of force the other boats can . The shape of it's curve is superior however, meaning the pos and neg area ratios. 

when you compare these areas , just like the electrical analog , just use the absolute values, meaning positive values . So the Bavaria looks like about 4 or 5 to one and the Hanse looks like under 2 to 1 (ratio pos/neg)

The smaller the boat is , the higher the static stability limit (LPS) needed to qualify for a particular offshore category, 0,1,or 2. 

I just tried to upload the offshore category table and it failed to upload 
both gif or jpeg , will have to get IT guy in here , anyway google it 

hope this helps/ kev


----------



## kevlarpirate

clarificationS;

1 think of absolute value as always positive
2 also the Bavaria cannot produce the "torque" instead of force. 

And to that end , generally, the bigger the boat is, the lower the LPS can be to qualify for a category or in a storm not get rolled , obviously as the boat gets bigger, the waves at a given sea state are smaller in relation (to the boat)

Kev.. PS I saw some of those videos you posted , very exciting , wish I were there !!


----------



## PCP

These are the original statements:



PCP said:


> The righting moment curve, the one that shows all righting moments at all points of heel, the one that can represent the total energy to capsize the boat&#8230; is the one that Archt. John Rousmaniere says that is "the best gauge , which any reputable boatbuilder and designer will provide"... The areas behind the positive parts of the curves represents the energy needed to capsize each boat. The point where the curve crosses for the negative part is the AVS point (point of no return). The area over the negative part of curve represents the energy needed to return a capsized boat to its original position.
> 
> Paulo





kevlarpirate said:


> ...BTW the expression is area "under" the curve no matter if the portion of the curve is in positive or below zero in negative territory
> ...Kev





kevlarpirate said:


> Paulo , it's just math talk
> 
> in this case , the curve looks like a distorted sine wave. If you take a function such as that and use calculus, you can determine the area under the curve by integrating . If that were say an electrical current flowing , we would refer to that area as the energy under the curve. Once the curve goes negative it is still energy, the sum of the two as the total energy even though one part is in negative territory , (below zero) and so we just think of it as the absolute value , meaning it has no sign (positive or negative)
> ..when you compare these areas , just like the electrical analog , just use the absolute values, meaning positive values . ...
> ...kev


So you are saying that the total energy required to capsize the boat is represented by the sum of the areas, the one under the positive part of the curve and the one over the negative part of the curve?

If not, please explain exactly what you consider wrong on my first statement.

Regards

Paulo


----------



## kevlarpirate

No , it is not the sum of those two areas. 

The ratio of those areas say 5 to 1 (pos vs neg) would mean that the energy needed to invert the boat would be 5 times the energy needed to flip the boat back upright from an inverted position. 

So , if a boat had a ratio of 1to1 pos vs neg, that would be really bad
like a catamaran , that would say that the boat was equally as happy to be upside down as right side up. On other end is say a 7 to 1 ratio of areas , where once inverted, it would take only a small heel angle (energy) to roll back through zero and flip back upright .

I am going to dig up some past posts by sailaway21 who explains this stuff way better than me. I leave too many gaps, 
have to run out now /later/ kev

but also remember this is just static bathtub stuff, 
oh and do this , take a wine glass, and a margurita glass (both with stems)
then seal the tops with saran wrap and a rubber band and do this experiment in the kitchen sink. have some fun / GFTD will get back


----------



## kevlarpirate

OK here , read sailaway21 posts. http://www.sailnet.com/forums/sailboat-design-construction/38919-limit-positive-stability-lps.html

starting 12-08-07 post no.6 .

so as the heel is increased the curve rises (righting arm increases) 
then it comes to the top of it's curve and that will be somewhere around 
where the rail meets the water. then you continue force the boat to heel 
and it will push back (torque) but not as much. The righting moment (torque)
will decrease to where at some angle where the curve crosses zero .
you could touch the keel (now above the water) on either side and the boat would roll in whatever direction the push came from. 
This angle is the limit of positive (and negative for that matter) stability

the angle of vanishing stability is a misnomer, the stability has vanished completely , so it should be called the angle of zero stability.

sailaway is very squared away, technical guy


----------



## kevlarpirate

I would also like to comment that the danger zone refers to the increasing angle beyond the highest part of the curve where righting moment is still positive , but rapidly decreasing. This is where if you become overpowered by the wind or rolled by a wave abeam that it is increasingly hard to recover and get the boat upright. 

More classic designs with deeper hulls have a higher angle where this top of the curve lands. This is readily overlooked as important. wider boats with 
no dead rise are very vulnerable here , look at the slope of the curve as it approaches zero righting moment angle. The steeper the curve, the less energy needed to keep you rolling (in the bad direction) 

I can illustrate with a Hobie Cat; for instance where you are flying a hull,maybe 15 degrees heel and within a few degrees of the peak righting moment and you get a puff which heels you a bit more and you find yourself dumping the main as fast as you can and still end up going over on your side.

On a cat , once you are in the danger zone , you are probably going to get very wet


----------



## PCP

After all it seems there is nothing wrong with this statement :



PCP said:


> &#8230;
> The righting moment curve, the one that shows all righting moments at all points of heel, the one that can represent the total energy to capsize the boat is the one that Archt. John Rousmaniere says that is "the best gauge , which any reputable boatbuilder and designer will provide" as opposing to "his" Capsizing formula "that is NOT a measure of stability range" just a "guideline".&#8230;.The areas behind the positive parts of the curves represents the energy needed to capsize each boat. The point where the curve crosses for the negative part is the AVS point (point of no return). The area over the negative part of curve represents the energy needed to return a capsized boat to its original position.
> Paulo





kevlarpirate said:


> &#8230;
> The ratio of those areas say 5 to 1 (pos vs neg) would mean that the energy needed to invert the boat would be 5 times the energy needed to flip the boat back upright from an inverted position.


It seems that you are only talking about the proportionality between the positive and negative area. Of course if the area under the positive part of the curve is two times bigger than the part over the negative part of the curve we will have a 2/1 proportionality and so on, that's clear and it is implicit.



kevlarpirate said:


> &#8230;
> So , if a boat had a ratio of 1to1 pos vs neg, that would be really bad
> like a catamaran , that would say that the boat was equally as happy to be upside down as right side up. On other end is say a 7 to 1 ratio of areas , where once inverted, it would take only a small heel angle (energy) to roll back through zero and flip back upright .


So, you are saying that Catamarans, because they have a 1/1 positive/negative ratio are really bad or unsafe sailing boats? And that a boat with a 7 to 1 positive/negative is a good and safe boat?

That makes no sense. You cannot be so simplistic in that analysis. A well designed cat will have several times the positive stability of a similar size monohull and the energy to capsize it would be several times bigger. And what real advantage would represent a boat with 7/1 ratio versus a 2/1 ratio if this one requires two times more energy to be capsized and has an AVS that will guarantee a reasonable time of recovery?

A boat when capsized (rolled) will lose the mast and can be partially flooded, and that will have a very adverse impact on its stability and on its recovery capacity. It will always be a damaged boat not to talk about the risk of hull damage, by the broken mast.



kevlarpirate said:


> &#8230;
> &#8230;but also remember this is just static bathtub stuff,


Yep! We are talking about what Archt. John Rousmaniere says that is "the best gauge , which any reputable boatbuilder and designer will provide" as opposing to "his" Capsizing formula "that is NOT a measure of stability range" just a "guideline".

Regards

Paulo


----------



## Jeff_H

Great discussion guys. I really agree with Sailaway's last point which is why I prefer the term "Limit of Positive Stability" to Angle of vanishing stability.

I want to jump into this discussion but do not have the time to do so in a meaningful way at the moment. KV I agree with you that statics is less of a critical part of the discussion about capsize than dynamics and would like to go through my thinking on the physics surrounding that issue and see how we agree and disagree, especially as it pertains to the OP about Comfort Ratio.

But for now I will simply quote Bob Perry's response to an earlier posting of my discussion of the uselessness of the Capsize screen formula.

"Jeff:
Many thanks for your common sense approach to this subject. I have been harping on the same thing for years.

Listen to Jeff.
you cannot reduce this ultra hydrodynamic situation to a set of 2 dimensional equasions.

Stop being silly. It's the sea. It is very big.

If the sea wants to tip you over it will tip you over.
The sea is big.
You are small."
http://www.anything-sailing.com/sho...e-Screen-Formula-and-the-Motion-Comfort-Index.

Cheers,
Jeff


----------



## PCP

Jeff_H said:


> ... I really agree with Sailaway's last point which is why I prefer the term "Limit of Positive Stability" to Angle of vanishing stability.
> 
> ..Cheers,
> Jeff


Now you got me confused Who the hell is Sailaway and what point are you talking about? He didn't post on this thread.

Limit of Positive Stability and Angle of Vanishing Stability are just names for the same thing. The denomination AVS seems to be much more used and words are just words, providing we are talking about the same thing

Regards

Paulo


----------



## kevlarpirate

paulo , in your first statement you missed the point that the bigger the vessel, 
(size & mass) the smaller the waves are for a given sea state. 

so a static curve on a small boat with say a 7:1 pos:neg ratio
will fare less well than a big boat with a say 4:1 
The offshore catagories show this but I can't upload it .
but I can give example here 

for cat 1, as example a 41 foot boat is required 130.6 deg
..............................a 45 foot .......................137
...............................a 61 foot........................109

The second quote I show that the higher the ratio pos:neg areas, the boat if inverted will stay inverted a far shorter time statistically in a given sea state .this is the point.

The conclusions re the cat , with 1;1 you are flat wrong . 
we are talking physics here not anecdotes about flooding and possible broken masts 

the last statement you make about the authors statements addresses my opinion that he perhaps wishes he never made any statements in the first place, because of political reasons. 

I suggest you start educating yourself at a higher level. Buy the books 
mentioned. You can also throw in VanDorns Oceanography and Seamanship
you need to start to appreciate the physics. I have them all, and read them.
They all say the same thing, some better than others. 
Now it is time for you to put in the time, I am not here to teach physics


----------



## blackjenner

sailingdog said:


> LOL...Hey Jeff, you do know you're replying to a thread from last summer, right??


Yeah. And I'm learning from it now.


----------



## kevlarpirate

I gave you the link to sailaways post , You didn't read it ?????

I also stated the confusion some may have with vanishing and zero 
stability , Vanishing stability is better represented by the decreasing moment arm from angle of max moment to the zero point . ( the danger zone)


----------



## kevlarpirate

corrections 
a 35 not 45 foot boat is required to have 137 deg LPS

also the smaller the waves are "relative" to the boat in a given sea state .
Also Paulo , a statement you said earlier is false re needing 50 kts of wind 
for any of these extreme situations to be encountered.

You can encounter this in relatively shallow water in or near sandbars 
in moderate winds where if you are a dummy, you can end up with a surfer size wave on your beam with the top 3 feet curling 

Also in an inlet with strong current opposing 15 kts of trade winds as you do in many Florida inlets.


----------



## PCP

KevlarPirate, this is my last post replying to you. Some of your posts, with special relevance to posts nº 20 and 35 show that you pretend to know a lot more than you really know about boat stability. I would not have minded if you had not chosen to hide that under a barrier of petulance and arrogance:

"I have been in physics professionally all my adult life.. I had Statics and Dynamics , and all the math and physics classes for an engineering degree many years ago These concepts are quite basic, you do not have to be a naval architect to understand them&#8230;but you do have to have an understanding of Statics and Dynamics&#8230; I suggest you start educating yourself at a higher level. Buy the books mentioned. You can also throw in VanDorns Oceanography and Seamanship you need to start to appreciate the physics. I have them all, and read them." 
<O</O
That's true that I am partially responsible for it (and I apologize) when I have said that you "show such an improper theoretical comprehension of a boat stability", even if what you were saying was not making any sense (that story of preventing a capsizing putting 500 lbs on top of the mast of a 37ft boat). But that it was also true that you had already started that path of arrogance, suggesting that Jeff, that we all know is a knowledgeable member, should take a class on statics and dynamics ( I am quite sure he had classes in statics and dynamics)
<O</O
But that is too much, at least for me. Anyway the books and the information you point to me are rather old (that does not mean that they are incorrect), and are not addressed directly to the stability of relatively small sailing boats. I prefer more precise information, more directly connected with sailboats and their stability. One of the best sources is the Westlaw Institute of Marine Technology (I believe it is in the US the best naval yacht architecture school) and they have published information on stability, on many types of boats, including monohull sailboats. 

The information available is the core of what is taught there, in what regards sail boat stability. Dave Geer (the Director) has published relevant information in many places, from the Institute magazines (very complete articles) to some "lighter" explanations on boat magazines. I have also read (on the subject) many "papers "published by European Naval architects, some that served as basement studies for the EC boat certification in several classes.
<O</O
Don't make me wrong I am not saying that all you say is meaningless, I just don't have the patience for your "style" . Anyway I have just come in this discussion because you have given too much importance to an old formula (capsize ratio) that I knew that had a very limited use and interest on today's assessment of a boat stability and that can be misleading. 

Nowadays all architects use computer generated stability curves to access boat stability and those curves are easily obtained. Even *Rousmaniere*, the creator of that formula says, that stability curves are the "best gauge" , that his formula "is NOT a measure of stability range" and that "too many people try to make way too much of it." 
<O</O
Fifty years ago stability curves were not easily obtained and boats were much more homogeneous in type, now those curves are very easy to obtain and sailing boats come in all forms and shapes. Today that formula serves no purpose. I think that *Bob Perry's quote* has put an end to this discussion (*posted by Jeff, post 42*). I would like to emphasize what he has said with another quote ( *Bob Perry*): *"I only use full stability curves to evaluate new designs. "*
*<O</O*
http://www.anything-sailing.com/sho...e-Screen-Formula-and-the-Motion-Comfort-Index<O</O

I have read that thread you have posted and I have found *Sailaway* posts interesting and informative. Nothing there that I can disagree with or that I could have not said. I also agree with you and Jeff that in what regards the assessment of capsizing risk of a given sailboat, the static information is only basic information and that other factors should be integrated on that assessment. Of course, I disagree that in a small boat the roll moment of inertia would play any significant part in that assessment (and I have explained why, on post 28).
<O</O
Finally, I would like to assure you, despite all you have said, that I have the necessary basis to understand the physics that are subjacent to the understanding of a boat stability. I have a degree in Architecture (technical University) and in 5 years of superior studies I have had 4 with theoretical and applied physics. Of course, what is important is not what you learn on University but the tools you acquire and that permit you to learn for the rest of your life. 

I believe that it is not new to you that some of the older yacht Naval Architects have not a degree in Naval Architecture and that has not prevent them to learn everything that was needed to understand everything about boat stability and boat behavior. Comes to my mind one of the most innovative and prolific boat designer, one that certainly will be remembered as one of the great Naval Architects of the XX century, *Jean Marie Finot*.
<O</O
He has a degree in Architecture and I believe he did never have the trouble to get a formal education on Naval Architecture. That hasn't prevented him to learn everything that was to learn about the subject and to become in fact, one of the best and most creative Naval Architects , the father of a whole generation of bright and talented young naval French Architects.
<O</O
http://www.finot.com/

Regards

Paulo


----------



## kevlarpirate

Paulo

This is simple Newtonian physics. 
.
BTW it is Westlawn, not Westlaw and I have known of them since the early 70's. A friend of mine attended, and graduated, he had to move up north which I would not do. It was available as a correspondence also but I elected not to based on advice I received from another friend who has passed now, Mark Soverel

He enlightened me how difficult it was to make profit building sailboats. As you know, he built a reputation early on. Mark was a surfer and his approach was to simply apply surfboard lines to sailboat hulls. Mark was bankrolled by his dad, those were our glory days, Mark was lucky and got to jump right in the business we all dreamed of doing. I ended up in high science, and made more money with a lot less effort. 

Now you wonder why I am boring you with this, so I will cut to the chase. 
Designers today have to deal with the same "swimming upstream"
as Mark described it to me. However these new boats have an additional problem and that is offshore categories. 

Methods for determining ultimate static stability are now computer modeled and can be manipulated to the point of garbage in garbage out. 
Tank testing at say Davidson Institute or the David Taylor facility is out of the question. I personally was involved at the David Taylor facility on a project where our bill exceeded my worst expectations. 

I can assure you adjusting the inputs in our modeling and adjusting the model itself could easily eclipse the empirical results we realized at the facility. 

The point of this is buyer beware and this is 2010, 
A little sobering I will say. Manufacturers have to be wary of being sued 
and so they are very careful when they push the limit of what they feel that can say. 

Less than technical sailors 
come to believe there is some new technology which has replaced 
old school teaching. Nothing is farther than the truth. 

Statements that huge gains were made when we advanced from IOR boats to IMS boats is hogwash. There were absolutely no huge breakthroughs. IMS boats were simply lightened up by 
removing lead and to maintain righting moment, they broadened the transom. Is this breakthrough? Hardly. I have no issue with that until the false claims start to emerge. For instance, as a result , the static stability curve worsened from the worst curves from IOR. They also needed big crews to make their numbers and the overlapping jib issue is bunk. 

Back to the early 50’s, we have a Flying Dutchman. Was that a breakthrough? Well yes, unless we go back 10 years earlier and compare it to a Thistle. Then we can go back to the 30’s and look at a Moth. These were dinghys and were able to plane upwind. The point is we new all this stuff decades ago

Can we make 30 foot planing boats today ? Absolutely. Is it breakthrough? If you think it is, refer to the above paragraph. 
But beware, they will have curves almost as bad as a catamaran. 
Initially stiff, which gives novice sailors a safe feeling but 
what they don’t know is that is paid for by a low angle tipping point. 

The issue here is lighter, wide transom zero dead rise boats are being advertised as safe with high static limits generated with complex models which buyers falsely feel safe with. 

Want some proof? try this , Go back to Jeffs post to the AVS calculator 
Jeff calls it convenient . Interesting that the LPS for whatever you put in is quite high. In fact it calculates the J-35 as 20 degrees higher than the USYRU 105 degrees. Now that may not 
create much question, but when I put in the numbers for my own boats I get a number OVER 180 DEGREES !!!
How can one have confidence with this???

Also, you say:

"I disagree that in a small boat the roll moment of inertia would play any significant part in that assessment (and I have explained why, on post 28)."

you are missing the basics here ...moment of inertia does not discriminate in size. It just scales, Newtonian physics rules

Moment of inertia is an integral part of the system whether it be a ship or a model in your bathtub.


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## kevlarpirate

Paulo . I read post 21 of mine and I can see how someone lacking the grasp of dynamics could have been mislead. However I cleared that up thoroughly in later posts. By post 35, I really took the time to help you and yet in reference to that post you also claim I don't know what I am talking about. 
It is unfortunate this became personal , 

I do conclude however that you are skimming my posts and not trying to understand them. I suggest that not only do you take the time to learn Statics and Dynamics , but also that you get past your emotion.

Catamarans when caught in a storm are notoriously dangerous by design
as are light weight sport boats.
As for Jeff; If he wants to talk with me and if we go into battle , that's our business. 

I am writing here for other readers who may be new to this and are doing internet searches to educate themselves. I have plenty of non biased knowledge to share. I will be monitoring posts to detect bias and misinformation 
All I can say to you is thanks for standing down here


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## Jeff_H

Kev,

I think that we should be able to have a reasonable dialogue on motion and capsize, both from a dynamic and static standpoint. I see no point in doing this as a battle, but I am certainly open to a constructive dialogue which may be helpful to those, as you say, other readers who may be new to this and are doing internet searches to educate themselves. 

You have said that you think that I come to this with a lack of knowledge of dynamics. You may or may not be right, but I have no intention of arguing that point. 

I would suggest as a format that we take this a step at a time. I would be gladly willing to make a series of posts that explain motion comfort and stability as I understand it, and certainly be open to your responses with corrections, comments and additional information. You have suggested that I come at this with a bias. I will try to keep this as scientifically based as I know how, so if you see cases where you think that that a bias has slipped in, please feel free to point this out. 

Some aspects of these posts may seem like baby steps, but I think it would be helpful to take this a step at a time so that a newcomer can follow the discussion and so that we can hopefully reach an understanding of the basic science before moving along. 

The one thing that I will not accept is allowing this discussion to include ad-hominum attacks. Personal attacks are not permitted under forum rules. I have no ax to grind with you and hopefully we can do this in a way that serves as a model of how to explore disagreements in principle in a civil manner, as well as, how to provide a clear explanation for complex topics for those who chose to read it and participate. 

Paulo, I know that this is an area of interest for you and so hopefully you will stick around as well. 

Respectfully,
Jeff


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## Jeff_H

To kick this off I will start with a couple basic examples on roll, heave, and roll moment of inertia and see if we are in agreement. 

1) If you had a boat that has form stability, but which has absolutely no inertia, no roll moment of inertia or non-form (weight) stability, (which of course cannot actually exist in real life) that boat would always sit at the same angle relative to the surface of the water. In other words, no matter where that boat sat on a wave, its waterline would essentially be tangental to the surface of the water. 

2) In that example the rate of change in the angle of the boat and the vertical rate of change would precisely follow the face of the wave passing below it. That boat might have reasonable motion comfort in flat water or small waves with a long duration, but would quickly become pretty uncomfortable in steeoer waves or more closely spaced waves where roll, pitch and heave would toss the crew around mercilessly. 

3) Of course if we took that example and added some inertia (bringing it into the real world), the boat would no longer instanteously change direction vertically or with regards to roll angle with the surface of the water. There would be a lag between the change in vertical height and angle of the wave face and the change in height and angle of the boat. 

4) In theory, this slowing in pitch and roll due to inertia would be more comfortable to the occupants since there would be less dramatic accelerations felt by the crew of the boat. 

Jeff


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## kevlarpirate

Jeff, yes except that in #3 you are not adding momentum, you are adding mass, so now acceleration will not be infinite. (and momentum results)

F=ma : F/m=a (no longer dividing F by zero ) 

but the energy dumped into the system is theoretically the same (with lower amplitude and longer time to keep energy same) In the real world that is damped by friction thus lowering the Q of the system.


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## Jeff_H

To continue: ( I am numbering the items so that they are more easily referred to in discussion) 

5) Motion is classified as being either Linear (also referred to as directional) or Rotational. 

6) Linear motion is described in one of three ways: surge (fore and aft), leeway (sidewards also referred to as sway ), and heave (vertically),

7) Rotational motion is also decribed in one of three ways: Pitch (fore and aft), yaw (rotation as seen in plan view) and roll (abeam which of course is side to side seen from bow or stern). 

8) All are slowed by inertia. In the case of linear motion, the amount of inertia is basically proportionate to the weight of the boat.

9). In the case of heave, the speed of vertical upward acelleration relative to the rate at which there a vertical change in height of the wave face is proportionate to the weight of the boat and also porportionate to the area of the waterplane (the area of the boat measured at the surface of the water) of the boat.

10) In other words in heave, going up a wave, a heavier boat will accelerate proportionately more slowly than a lighter boat with an equal waterplane. 

11) The waterplane comes into play on the acceleration of the upward climb since the force imparted into the boat is roughly equal to the plan dimension of the boat. If we compare two boats of equal waterplane, the boat with the smaller water plane will sink lower into the wave than the boat with the larger waterplane. That small amount of reduction in the initial travel distance as the boat lifts results in the boat with the smaller waterplane having slightly less acceleration in effect acting as shock absorber. This effect is more noticable in closely spaced waves.

12) At the top of the wave, the boat's inertia will carry it vertically beyond past the point that the wave is trying to lift the boat. Normally the carry is is only a small distance but in extreme cases; a steep wave with lots of speed, a boat with a lot of inertia and a large water plane, the boat can be thrown clear of the top of the wave. In this case it is possible for the boat to get out of phase with the back of the wave and impacting quite solidly and uncomfortably.


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## Jeff_H

KP: I agree with your post 53. My description in my post 52 was an over-simplification of the physics. Adding momentum will take the motion of the boat out of phase with the waves and adding friction will reduce the overall amount of erergy available to create motion so the amount of motion that occurs is reduced.

Jeff


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## Jeff_H

13) In other words, I think that we are saying: The amount and speed of motion a boat experiences is related to the amount of energy that is imparted into the boat, the ability of the boat to store that energy, and the ability of the boat to dampen (disburse) that stored energy.


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## cormeum

Jeff_H said:


> 13) In other words, I think that we are saying: The amount and speed of motion a boat experiences is related to the amount of energy that is imparted into the boat, the ability of the boat to store that energy, and the ability of the boat to dampen (disburse) that stored energy.


Change "speed" to "momentum" and you've got it.

For the same E and large M would entail a small delta v. The energy capture may be the same, but the change in velocity would be quite different depending on M.


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## kevlarpirate

men,
so how would you like to describe motion comfort?

for instance I see the formula says a Westsail 32 is more comfortable than a Santacruz 50.... hmmm. but hold on, if you close your eyes and cup your ears
so you lose the sensation of speed on the SC, well then there is a noticeable difference from having vision and speed sensation . I have done this , it's a cool trick.

I agree that the psychological stimulation speed offers can dampen a certain level of discomfort. Personally I have more issues with sitting discomfort
from cockpits with low combings that dig you in the back when you are on the low side 

I like the snappiness of my 740IL BMW far more than the cushy ride of my sisters Caddy. both are land yachts, but I have also never driven blindfolded. perhaps I should be the passenger sometime. Kev


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## PCP

Jeff_H said:


> 13) In other words, I think that we are saying: The amount and speed of motion a boat experiences is related to the amount of energy that is imparted into the boat, the ability of the boat to store that energy, and the ability of the boat to dampen (disburse) that stored energy.


The boat motion is also related with the LWL. Nothing to do with inertia though.

Paulo


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## seabreeze_97

The Motion Comfort Index is not intended to compare boats of different class (and by class, I mean relative size/hull dimensions). In other words, you would not use the numbers to compare a Westsail 32 to a SantaCruz 50. It's intended to make comparisons of similar boats like a Westsail 28 and a Bristol 32, for example. Toss in the J30 for kicks. The J30 will run rings around the other two, but it's not as comfy. Let's say you have a 30 footer and a 45 footer that have the same index number, or the 45 footer has a somewhat lower number. The 45 footer will still be more comfortable. Speed aside, the longer hull has other virtues, one being relative comfort when compared to shorter hulls. As Ted Brewer stated, it is a quick reference to compare similar boats.


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## sailingdog

Jeff_H—

I'd point out that your first four elements describe a large cruising catamaran fairly well—in that a cruising catamaran has exceptionally high form stability, tends to sit on the water and move with the surface of it, and describes the quicker motion often seen in multihulls. Also, compared to a monohull of the same LOA, the multihull will have much lower inertia, not having the mass of the ballast that a monohull has.


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## PCP

sailingdog said:


> Jeff_H-
> 
> I'd point out that your first four elements describe a large cruising catamaran fairly well-in that a cruising catamaran has exceptionally high form stability, tends to sit on the water and move with the surface of it, and describes the quicker motion often seen in multihulls. Also, compared to a monohull of the same LOA, the multihull will have much lower inertia, not having the mass of the ballast that a monohull has.


Yes, that have crossed my mind . That is even more true for a sporty light cruising or racing multihull.

Regards

Paulo


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## Jeff_H

A couple quick responses: 

Cormeum (post 57): 
I think that I agree that you are correct in the direction that you are suggesting, but I would suggest that there are two separate issues here. 

I think that to be more accurate, my earlier paragraph #13 (post 56) should not have referred to "Speed", but to "rate of change in speed", in other words "acceleration". 

I would suggest that "momentum" is what was meant by the phrase "the ability of the boat to store that energy" within my earlier paragraph #13 (post 56) .

Paulo: 
I agree that LWL is a factor in the motion comfort of a boat but only as it relates to specific types of motion. LWL comes into play when discussing rapid deacceleration in surge due to the collision with a wave when going upwind and also is a big factor when discussing pitch.

There are cases where a boat with a long enough waterline to bridge several waves when passing through several closely spaced waves at a time can experience a more comfortable motion since the factors that cause heave or roll so within an individual waves may be seen as counteracting each other as the boat experences several crests and peaks at the same time. I would think that this is a pretty rare condition, but it was one of the things that I noticed in the short chop of the Chesapeake going from a 28 footer to a similarly proportioned 38 footer.

SailingDog: I would agree with you that a large, light multihull comes probably comes closest to the model described in points 1 through 4.

Jeff


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## blt2ski

Seabreeze has described the motion comfort number while not directly, best as he quoted Ted Brewer the designer of the formula.

But as noted by others, and to a degree by seabreezes quote of TB, some boats in different times and places will be more comfortible than others. Some what is more comfortable in say 30 knot winds in Puget sound where I am with closer space 3-4' waves, ala a 50' boat vs my 30' boat, now take this out to the ocean, yes granted the waves will be taller, farther spaced and less steep, my 30'r may sail up and over, mean while the 50'r is pitch poling the waves. Where I was pitch poling etc the waves in Puget Sound to a degree. 

Not sure that one will come up with a how this formula works per say, other than, one should compare like boats and sizes vs the OP comparing IIRC boats from all shapes sorts and sizes. Likewise, to compare a cruising cat to a SC50 or a Westnail style boat is not good either using this formula. 

My 02 for what it is worth, probably less than 01, maybe .00001!

Marty


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## sailingdog

I'd point out that the quicker motion of a multihull is often so different from that of a monohull that people who get seasick on monohulls may not get seasick on a multihull. Then there are people who are affected by the quickness of the motion on a multihull that get seasick on one but are fine on a monohull.... then, finally, there are the poor bastages who are seasick on anything that floats.


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## kevlarpirate

seabreeze, 
I was pointing out that when I went objective and covered my eyes and ears ( I guess you could also go down below and put a blanket over your head)
The SC50 was pretty jerky. considering it only weighs 18000 and is all waterline, then it approaches the first example jeff put forth. 

As for the TB expression, it is a non linear equation s therefore you may expect some breakdown when you get out of some central bandwidth.

You may conclude it is bandwidth limited , but still in my case with the Weatsail and the SC, it seems to still hold up. 

IMO comfort is not objective. Excitement over rides comfort. 

Jeff, yes I knew what you meant . the equations of motion involve
mass, force, acceleration (dv/dt) and velocity and it is better to stick with those terms. 

I realize you make effort to describe these issues in laymans language
so other people can learn. 

I can also say that mass in motion (inertia) is the 800 lb gorilla. 

My Ericson 46 is very observably more comfortable than the SC50.
Considering its mass is double the SC that would be expected.

This is observable both at rest on a mooring can and also underway.
but again, if you were to interview crew after the SC sailed a circle around us I would be willing to bet the SC crew never even considered discomfort as an issue.

Where it would be an issue would be crew fatigue and injury due to accumulated high accelerations throwing someone off balance.


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## PCP

Jeff_H said:


> ...There are cases where a boat with a long enough waterline to bridge several waves when passing through several closely spaced waves at a time can experience a more comfortable motion since the factors that cause heave or roll so within an individual waves may be seen as counteracting each other as the boat experences several crests and peaks at the same time. I would think that this is a pretty rare condition, but it was one of the things that I noticed in the short chop of the Chesapeake going from a 28 footer to a similarly proportioned 38 footer....
> Jeff


Yes, that's what I mean, but I don't agree it is a rare situation. On the med and in any other places where it is usual that kind of short period steep waves, the motion comfort of a 30ft boat would have nothing to do with the motion comfort of a 50 or 60ft boat (on those conditions). The 30ft will be bouncing around, up and down, losing momentum and crashing at each wave. A 50ft light modern powerful sailboat will pass on the top of the several crests almost on a linear movement, at speed, without losing much momentum.

Believe me, I have experienced that situation (a lot) and even a 36 ft will not be much more effective. For the kind of wave period we experience here, I believe that you will see a really big difference with a boat over 42ft.

In what regards motion and speed, the importance of the LWL is so noticeable (here, where I sail) that it is one of the reasons I have sold my boat (36ft) and I am lookig for a bigger one (42 to 45ft). Not in every sail condition, but just when things are not easy.

Regards

Paulo


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## Jeff_H

Paulo,

I agree with your comments about venue, and the importance of wave length and boat length. Historically, popular boat lengths often related to the prevailing conditions. Anecdotally, here on the Chesapeake, when they began motorizing workboats there was a belief that work boats needed to be approximately 42 feet long for them to be a comfortable working platform. This length corresponded being able to bridge several waves in what was perceived to be the prevailing wave period.

Regards,
Jeff


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## kevlarpirate

"A 50ft light modern powerful sailboat will pass on the top of the several crests almost on a linear movement, at speed, without losing much momentum."

Paulo , you obviously have never done foredeck work on a 50 in these conditions. 

Hint: knee pads and 
one hand for the boat, one hand for yourself


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## blt2ski

kevlarpirate said:


> "A 50ft light modern powerful sailboat will pass on the top of the several crests almost on a linear movement, at speed, without losing much momentum."
> 
> Paulo , you obviously have never done foredeck work on a 50 in these conditions.
> 
> Hint: knee pads and
> one hand for the boat, one hand for yourself


What size waves are we talking/dealing about? There are some wave sizes where a 50' boat will cruise thru 3-5 wave crests, and a 30'r will be bouncing up and over. There are some where the 30'r will be sailing up and over, meanwhile as you say, the 50'r is crashing and bobbing.

To sit at you puter and say that someone has not, they may not have, but still one can always come up with a situation in which we are talking about, that will be counter to a comment.

marty


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## kevlarpirate

I am talking about 3-5 foot waves going upwind to a weather mark and setting spinnaker meaning you can be up there for many minutes.. I have done this plenty, Don't think for a second I sail from my desk in front of my computer. I have done foredeck on dozens of boats in all conditions , short chop and all and I have done it since 1971. 

A SC50 weighs 16000 total. That means when you hit an oncoming wave , you feel it plenty !!!!! the bow is totally hollow, weighs nothing,and has plenty of wetted surface area

I have more lead in the keel of my 46 than the entire SC50 weighs

I see nothing so far that voids the formula. mass rules, that's why it's in the numerator, sorry, and one shaky anecdote is not enough to throw it out. 

I see this thread is off point now, getting bogged down with opinions not physics


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## Jeff_H

Sticking with the physics, to continue with the discussion in post 54 para 11 and 12 which was discussion of the factors affecting motion due to heave: 

14) Several factors impact the area waterplane of the boat, but in general, the lighter the boat and the deeper the weighted average depth of canoe body, the smaller the water plane. In a general sense, since the amount of heave is proportionate to the mass of the boat and the areas of ite water plane, a lighter boat with a proportionately smaller waterplane (proportionately deeper cane body) may actually have a more comfortable heave motion than a heavier boat with a proportionately larger water plane.


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## Jeff_H

Way back in Post 58, Kev asked a very valid question; _"men, so how would you like to describe motion comfort?" _

If I had to propose a draft of an answer, I would suggest that a boat design that had desirable motion comfort characteristics would be a boat met some basic criteria in terms of balancing the shape of the boat (bouyancy distribution) and the weight distrubution within the boat so that the boat minimized both the amount of motion and the acceleration/ deacceleration felt by the crew. 

Off topic slightly, I also see this as being potentially good for performance since this also maximizes the amount of steady water and air flow over the foils. 

Jeff


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## PCP

kevlarpirate said:


> "A 50ft light modern powerful sailboat will pass on the top of the several crests almost on a linear movement, at speed, without losing much momentum."
> 
> Paulo , you obviously have never done foredeck work on a 50 in these conditions.
> 
> Hint: knee pads and
> one hand for the boat, one hand for yourself


You continue to assume what I know and what I don't know and I don't understand why. What is wrong with you?

As I have said, one of the reasons I have sold my 36ft boat was its shortcomings in what concerns sailing against the wind in short period steep waves, a kind of waves very common on the Med. It seems obvious that if I say that I want a bigger boat (at least 42ft) to sail faster and more comfortably on these circumstances is because I know that a bigger boat will sail faster and more comfortably.

I know that, not only for having a look at the motion of bigger boats that have sailed past, nearby, but because I have already sailed bigger boats on those circumstances. Particularly I have sailed a 44ft used for racing on the Solo circuit in Spain. That boat has the same type of hull design (it's even from the same manufacturer) and I have sailed it for several days, sometimes just with the skipper on muscled conditions, and yes, with only two guys on deck, both of us have made foredeck work. Yes, on the conditions I have described, compared with the 36ft, the 44ft boat is much more stable, comfortable and fast.

Regards

Paulo


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## kevlarpirate

jeff
I agree , I don't follow the "deeper the weighted average"
but I think I know what you mean. 

If the boat were designed for comfort , and that comfort was defined 
as minimum acceleration in all motions , both translational and rotational 
then we could model that for a set of given sea states and wave arrival angles.
Of course then the waves will come from a different direction and things change. I don't know what this boat would look like , but it could be modeled half way decently, and If i were to take a stab, i say it would have deeper sections as you describe


If we used accelerometers and not people , we may find no closure due to human emotions, like the desire for speed (winning feeling) as I mentioned before in my example. 

Also , on the Westsail / SC50 example I really did close my eyes, I have many boats of friends I get to sail on and I do this every time for fun. 

One issue not mentioned however is that even though the WestSail and the SC may have similar comfort or discomfort, numbers, you will be subjected to the "discomfort" much longer on the Westsail say on a long bumpy passage. 

Just suppose we sailed a test group of people down below having dinner where things move around and spill and there were no connections to the outside world, visual or audible and they didn't know which boat they were on because the interiors were made identical , and these boats sailed side by side at the same time and then we switched these groups to the other boat and did it again.


You may find you would rather be on the Westsail........ or not .
personally I don't know , but i sure would like to do that experiment


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## kevlarpirate

Paulo
I am not disagreeing that bigger boats are not faster and more comfortable.
You want to power upwind in big developed chop, and get somewhere in comfort
and stay dry. 

Ask yourself; do you NOT want to hear the boat pound and feel it shudder. If you get a strong gust and you heel say 35 degrees, would you like your helm to still remain balanced, and still drive with two fingers
Do you want a dry foredeck?

If you want these things and a nice motion and a quiet interior , then choose carefully and spend the money on mass and not high tech materials and light weight bleeding edge design. 

Boats going upwind are still in the displacement mode, no miniscule upwind speed gains justify the price paid in motion discomfort, wetness, helm imbalance
and below deck noise. 


and if you want to know what is wrong with me , you will have to ask my wife,
I will say nothing, lips are sealed 
kev


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## Jeff_H

Kev:

Before I start on topic, I need to put on my Sailnet Moderator hat for a moment. In the course of this discussion, you have made a number of belitttling remarks toward several other members. Frankly, within reason, I don't care what you say about me, but I am requesting that you tone down your disparaging remarks towards other members.

It is perfectly acceptable and encouraged to make comments directed at the specifics of a post if you disagree with another poster's points in an effort make your case by explaining where you think they may have gone wrong. But it is not acceptable to make comments that target your perception of that poster's experience or perceived biases.

In Paulo's case, I have had ongoing discussions with him. He is an experienced sailor who has made a effort to understand these issues in a very disciplined way, reading all of the classic texts as well as recent papers on the subject. I ask you to treat him with the respect that is expected of all SailNet participants.

And now back to the subject: To address your comment from your post #75 _"I don't follow the "deeper the weighted average"_
_but I think I know what you mean."_

I apologize for that unfortunate choice of words. I used the phrase "deeper weighted average" as a way of trying to put this concept into plain English. I think this is a case where I knew what I was trying to say and so chosing that phrase made sense to me at the time, but in hindsight I realize that it probably would mean very little to anyone else.

The point I was trying to make is that a boat that has a comparatively deep and full canoe body can have a comparatively small waterplane. Wile there is relationship of water plane area to the height of the vertical center of buoyancy, the vertical center of buoyancy does not tell tell the entire story since the issue is one of cross-sectional area and the distribution of the submerged volume.

I also want to comment on the implication of your very valid point _"If the boat were designed for comfort , and that comfort was defined as minimum acceleration in all motions , both translational and rotational then we could model that for a set of given sea states and wave arrival angles. Of course then the waves will come from a different direction and things change. I don't know what this boat would look like ..."_ I would suggest that we walk our way through the physics and see if we come to an agreement, as well as how we define 'motion comfort" and then move on to trying to figure out what that boat would look like.

And while I do not want to jump to conclusions, I do want to comment on your suggestion in post #76 _"If you want these things and a nice motion and a quiet interior , then choose carefully and spend the money on mass and not high tech materials and light weight bleeding edge design..."
_
I will suggest that while mass can be helpful when looking at heave, adding mass in and of itself may not help with the other forms of motion. Using motion comfort as an important design criter in shaping of the hull, designing the weight and buoyancy distribution, and as a criteria in the structural engineering of the boat can be as productive or even more productive in producing a boat with a maximized motion comfort that simply adding mass. But I suspect this comment is getting ahead of the discussion at hand.

Respectfully,

Jeff


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## PCP

Jeff_H said:


> The point I was trying to make is that a boat that has a comparatively deep and full canoe body can have a comparatively small waterplane. Wile there is relationship of water plane area to the height of the vertical center of buoyancy, the vertical center of buoyancy does not tell tell the entire story since the issue is one of cross-sectional area and the distribution of the submerged volume. ...
> Jeff


I would like to make a clarification here. Nothing you have said but an association most people do.

Not all boats with a large beam have a big waterplane. A new generation of cruisers that have as inspiration Open boats, boats designed without being constricted to perform better under a set of rules (IMS, IRC) have a large beam and stern but a small waterplane, as have their racing cousins.

On sailing position, these boats that heel less than a "normal modern big production cruising" and much less than the "deep full canoe body" that Jeff is talking about, have a small and asymmetric waterplane, and small because having a very deep bulb and having a high tech construction, they are very light. They also have very fine entries.

I once saw some drawing from Rodger Martin on the asymmetric waterplane of its 40 class boat (sailing position) and I was quite surprised with the shape. The waterplane was small and the shape resembled the shape of the racers from the beginning of XX century: Long and narrow.

These boats have a very distinct sea motion. They have not the motion of a deep full body canoe with a similar waterplane area, but they also have a very different sea motion compared with a traditional beamy boat, with a much bigger waterplane and "fat" entries.

By the way, one of the items that has not been referred as important, in what concerns boat motion comfort is heel and I think it is quite important.

It is very different to prepare a meal with 15 degrees of heel or with 30 degrees, as sleeping or moving around.

Regards

Paulo


----------



## kevlarpirate

Jeff, no worries, just trying to save Paulo some headaches and money.

If he wants a flat boat, he will most likely have a bad "computer generated" ahem.... static curve to sleep with. That's his choosing, sweet dreams

If he wants high tech thin materials , he will have a noisy interior, 
and be serenaded by slapping waves against his hull all night long while tucked into one of those nice coves there in the Med. 

If he wants to be wet and get thrown about on the foredeck of an ultra light boat, fine by me.

if he doesn't mine hot coffee spilling on himself when his 44 foot 12000
boat hits some chop , then I don't mind either.

If he doesn't mind having to ride 6 feet above the water on the high side rail to steer, fine too 
If he doesn't mind having to steer perfectly in the slot 100% of the time and be constantly playing the main, that's great, good exercise too. 

by the way, heel is a good point , and to that, I have a variety of headsails and typically use smaller ones and never go over much over 20 degrees.

I often use a maxi roach main, and a 100% full hoist 4 batten North 3DL blade ,mast head on a self tacking track , and below 14 kts, I get within a tenth or two of my target numbers . Works for me . I can take that rig up to 20 kts true before i start bleeding the main. 
this is with all crew in my very comfortable warm and dry cockpit having beer and laughing away.

Anyway, it sounds like Paulo knows which way he would like to go, so after he buys the boat and logs some hours going up in 5 foot chop, I'll wait for the report.. 

All the best Paulo , kev


----------



## sailingdog

I'd point out that none of these formulas were created with multihulls in mind and fail miserably when more than one hull comes into play.


----------



## kevlarpirate

Jeff, the illustration I gave about the eating dinner down below 
was so no one would know what the speed of either of the the boats were
so that knowledge of speed would not affect their decision as to which boat was more comfortable. The remaining inputs would be substantially reduced to what extent the dishes are sliding around and how often your shoulders were bumping the guy next to you. 

As for mass, it is the biggest single factor in reducing impulse because F=ma. Impulse is defined as a very quick acceleration. 

We assume mass is distributed fairly equally between different boats.
So that if one boat had a heavier hull, keel, it would also have a heavier mast and a heavier deck so those proportions would scale in a linearly between the boats.

As for a definition of what comfort really is, that is subjective. 
If you know that you are going to be out there for twice as long as anyone else, well I would say that in itself is a discomfort, mental not necessarily physical.

As a note, IMO, I don't think Paulo really cares about comfort. I think he wants speed. Perhaps he wants it all. 
My point is that he can't have it all. Any manufacturer of a sport boat 
who adds 300 lbs of interior and calls it a cruising version should be spanked.

Yes , you can cruise in it , but to dupe someone into thinking it will be comfortable only means that that someone has never cruised any where.

Boats going upwind will be in the displacement mode, when you crack off
to 60 BAW, a sport boat will be noticibly faster

The single most important ability of a sailboat is it's ability to sail upwind
in strong winds and a developed sea without getting beat up. This is my opinion and also the opinion of many well seasoned designers. I have been in many situations where this ability became very important to the safety 
of boat and crew. 

Many sailors would rather sail off the wind , that's fine , we all have our preferences

kev


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## sailingdog

Kevlar-

No, I don't think you can assume anything about mass distribution For instance, if you take two boats of exactly the same MASS, LOA, Draft, etc, but one is built using solid laminate and the other is built using Divinylcell cored laminate, then the keel could be significantly heavier on the first boat than the second, while having a much lighter, yet stiffer hull, deck and such...



kevlarpirate said:


> Jeff, the illustration I gave about the eating dinner down below
> was so no one would know what the speed of either of the the boats were
> so that knowledge of speed would not affect their decision as to which boat was more comfortable. The remaining inputs would be substantially reduced to what extent the dishes are sliding around and how often your shoulders were bumping the guy next to you.
> 
> As for mass, it is the biggest single factor in reducing impulse because F=ma. Impulse is defined as a very quick acceleration.
> 
> We assume mass is distributed fairly equally between different boats.
> So that if one boat had a heavier hull, keel, it would also have a heavier mast and a heavier deck so those proportions would scale in a linearly between the boats.
> 
> As for a definition of what comfort really is, that is subjective.
> If you know that you are going to be out there for twice as long as anyone else, well I would say that in itself is a discomfort, mental not necessarily physical.
> 
> As a note, IMO, I don't think Paulo really cares about comfort. I think he wants speed. Perhaps he wants it all.
> My point is that he can't have it all. Any manufacturer of a sport boat
> who adds 300 lbs of interior and calls it a cruising version should be spanked.
> 
> Yes , you can cruise in it , but to dupe someone into thinking it will be comfortable only means that that someone has never cruised any where.
> 
> Boats going upwind will be in the displacement mode, when you crack off
> to 60 BAW, a sport boat will be noticibly faster
> 
> The single most important ability of a sailboat is it's ability to sail upwind
> in strong winds and a developed sea without getting beat up. This is my opinion and also the opinion of many well seasoned designers. I have been in many situations where this ability became very important to the safety
> of boat and crew.
> 
> Many sailors would rather sail off the wind , that's fine , we all have our preferences
> 
> kev


----------



## kevlarpirate

Motion behavior (as measured by accelerometers) will show us as we lower the mass, higher accelerations will result, this is both in translation and rotation.

So if you use the lighter materials as you say, accelerations will go up. for instance a carbon fiber mast will produce higher accelerations to the boat both roll and pitch.

I assume you meant you could have a heavier keel in the second boat , not the first (to keep total weight the same) ?

So are we talking comfort here or are we talking ultimate static stability?

If we are talking comfort , which would be defined as low accelerations as versus higher accelerations then the boat with the lower mass and moments of inertia (the cored boat you describe) will have higher accelerations and therefore lower comfort.

My point was that these boats have densities fairly close to each other, and therefore will behave in similar fashion
The use of words (much lighter and significantly heavier) are really in the range of a few tens of percent, and when those individual components are applied to the entire system, the desired results are less than may be expected.

If we move this conversation into the subject of ultimate static stability, we agree it is a simple experiment to show a lower CG produces a better static curve, however in the big ocean, the world of dynamics now come into play ,specifically moment of inertia.

reference: Relation Between Torque and Angular Acceleration
scroll to the bottom and see that moment of inertia for a thin rod (mast) goes by length squared, L, and for a cylinder (hull) it increases by radius squared, r

tank testing shows the importance of dynamics:

" The VCG can be lowered by a longer keel or by having more ballast (weight of the keel) at the end of the keel. However, according to Adlard Coles' "Heavy Weather Sailing" thirtieth anniversary edition, "The effects of large movements of the VCG on the propensity to capsize was surprising small".

Manufacturers claims and explanations cannot get around the laws of physics, therefore any and all claims should be carefully evaluated.

Newtonian physics has served us now for 400 years and will continue serving us


----------



## PCP

Kevlarpirate, it is very difficult to have a meaningful discussion with you. Besides the arrogance you seem to put very little discipline and methodology in the way you think. You think more like a pirate and less like a scientist .

As an example look at this:

I say on post 67: *"In what regards motion and speed, the importance of the LWL is&#8230;noticeable*."

On post 69 you imply (disagreeably) that I don't know of what I am talking about.

On post 76 you agree with what I was saying on post 67:* " I am nor disagreeing that bigger boats are not faster and more comfortable"*.

It is not possible to discuss anything this way .

Five years ago, on this forum I have posted a thread about this subject (seaworthiness, boat design and comfort) and as you can see, I was saying about the same things you are saying now.

Of course in 5 years I have learned a lot more and even if what I was saying is basically correct I have found that there were other points to consider, some technical others that have to do with living in the real world. People have a certain amount of money (not much, unfortunately) and they want to buy the more comfortable, seaworthy and fast boat they can get, and that is what really matters to the vast majority of people.

I suspected that I was basically wrong on the way I was seeing things because the best world Architects were not designing (not even for their personal use) the kind of boats I thought they should be designing and, because I don't have your Ego, I started to suspect that I was not understanding something. Since then I have a much better understanding of what they are doing and why and that has permitted me to have a much better understanding of boat design, the advantages and disadvantages of each type, even in what motion comfort is relevant.

A quote of some of the things I have said on that thread:

"....And about sailing, there are many differences in the kind of sailing (traveling). There are the ones that want to go as fast as possible with a full crew, others want good speed but a boat that can be easily solo sailed, others want maximum comfort in a seaway others an optimized safety, for the size of the boat. There are a lot of compromises to be made (in hull shape and rig), originating completely different boats, depending on the assumed different priorities&#8230;..

It seems to me that you think that weight (mass), besides the one needed to give the boat stability) is always a bad factor in a sail boat.Although I agree that mass is always a bad factor in a racer or even in a cruiser-racer, it is not (in my opinion) in a pure cruising boat with priorities aimed to have an easy motion, maximum safety and lots of autonomy. 

&#8230;. I believe older boats, even old racing boats, are normally "less radical" than most of modern boats and have a smoother sea movement. They have a less flat hull and have more ballast, depending less on form stability&#8230;&#8230;"

http://www.sailnet.com/forums/general-discussion-sailing-related/11338-how-heavy-too-heavy-ii.html

Regarding this thread and your posts, instead of discussing each point at a time you make a lot of claims and statements as if you knew everything about this topic and other opinions should not even be considered. I would say that, if not for Jeff (he asked me), I would not be around this discussion. I like to learn and I have learnt a lot in the last years, but I doubt I can learn something that way.

Let's see if I can answer some of those somewhat disconnected statements that you have made:



kevlarpirate said:


> &#8230;, just trying to save Paulo some headaches and money.
> Anyway, it sounds like Paulo knows which way he would like to go, ... &#8230;..As a note, IMO, I don't think Paulo really cares about comfort. I think he wants speed. Perhaps he wants it all. My point is that he can't have it all.
> 
> Any manufacturer of a sport boat who adds 300 lbs of interior and calls it a cruising version should be spanked.Yes , you can cruise in it , but to dupe someone into thinking it will be comfortable only means that that someone has never cruised any where.
> kev


It seems that you know more than myself, regarding what I want  . Fact is that I am quite sure that I can live happily with different types of boats (each has its own advantages and disadvantages) from broad sterns to canoe type boats (small beam). It all depends on what appears on the market at the (very) right price.

What I really know is what I don't want and that is an old designed boat. I want a modern design, a fast seaworthy boat, adapted to solo sailing with an interior suited to cruising and a boat that is fun and enjoyable to sail. I also want a boat that can go better than my older one against the wind on short period waves.

Comfort is one of the variables. Certainly I would not have a slow boat or a boat that is not agreeable to sail, but to be more or less comfortable is a question of tradeoffs. What do I lose on comfort, what do I gain on seaworthiness or speed? Each (kind of) boat is a case, to be studied separately, as the occasion arises and anyway, this is not relevant to this thread.



kevlarpirate said:


> &#8230;,
> If he wants a flat boat, he will most likely have a bad "computer generated" ahem.... static curve to sleep with. That's his choosing, sweet dreams
> If he wants high tech thin materials , he will have a noisy interior,
> and be serenaded by slapping waves against his hull all night long while tucked into one of those nice coves there in the Med.
> kev


I am pretty sure that I know more than you about stability curves, that, as Bob Perry has said (or any other boat designer will say), are the tool that you use to access boat stability, while designing it.

You seem to have a comprehension of what is the goal in designing a certain type of stability curve, but wrongly assumed that a certain type of Stability curve is the model from all other types of sailboats. Different sailing boat types have different kinds of stability curves that show the advantages and shortcomings of each type of boat, in what regards stability. In the last years I have looked over many different boat stability curves, trying to understand the options the boat designers have intended in designing a boat with that kind of stability.

You are not going to learn much if you assume that there is a correct type of stability curve and that all the others are wrong.

About hi-tech materials and the noisy interior while at anchor, you are wrong.
Old boats (and some modern ones) are built with a single skin (solid laminate) while hi-tech boats used a double skin with a core at the center. The double cored skin will insulate the boat from sound and temperature far better than the solid laminate, no matter its thickness.



kevlarpirate said:


> &#8230;,
> If he doesn't mind having to ride 6 feet above the water on the high side rail to steer..If he doesn't mind having to steer perfectly in the slot 100% of the time and be constantly playing the main, that's great, good exercise too.
> by the way, heel is a good point , and to that, I have a variety of headsails and typically use smaller ones and never go over much over 20 degrees&#8230;..
> kev


That is a very confusing statement. You mean that if in your boat you can go safely faster but have a heel superior to 20 degrees you would change for a smaller headsail, going slower? I am not that kind of sailor and I don't think you are either.

Different boats are designed to sail better and faster at a determinate angle of heel and almost all racing boats (older and new) and all narrow beam boats are designed to sail better (close to the wind) around 25 or 30 degrees of heel. My boat worked that way and yours too.

The only boats that are designed to sail with not much heel are multihulls and modern boats based on the design of Open racing boats, boats with a big stern and two rudders. These boats are designed to perform between 10 and 18 degrees of heel. You are not going faster if you push the boat and can even go slower.

If this kind of boats heels very little, how can I go 6ft over the water?
And if this kind of boats are designed for max stability and solo sailing why do you say that I would have to "to steer perfectly in the slot 100% of the time and be constantly playing the main"? That is quite the opposite, these are the most forgiving boats, boats that are made to go on autopilot on bad weather while their solo sailor is sleeping or resting in the interior.



kevlarpirate said:


> &#8230; The single most important ability of a sailboat is it's ability to sail upwind in strong winds and a developed sea without getting beat up. &#8230;
> Many sailors would rather sail off the wind , that's fine , we all have our preferences kev


Certainly a sailboat should have the ability to go upwind but to make that its most important ability, I disagree. Even in what concerns racing boats, particularly Open formula boats where you have the freedom to design more or less beamier boats, the boats designed for Open races are big transom boats, boats that can go well upwind but that are optimized to sail downwind.

That means that even on circumnavigation races going close upwind is far from the prevalent conditions. That is a lot more relevant if we consider cruising. Cruisers only go against bad upwind conditions if they cannot chose otherwise and in 99% of the cases they can and wait for the right wind.

Englishmen have a say: *"Gentlemen don't go upwind"*.

I would not be so adamant, but going close to the wind in bad weather certainly is not the first choice for cruisers.

Of course, I agree that, for safety reasons, a boat should have the ability to "sail upwind in strong winds and a developed sea" but making a priority into being able to do that and moreover in a relative comfort, it seems a vast exaggeration. Anyway your term "beat up" is imprecise. If it means what I think (pounding?).

Most modern big production sailboats have that ability, depending on the wing angle. A boat optimized for those conditions can go at 30 degrees or slightly less and a typical mass production cruiser can go at 45 degrees. 
Optimizing a cruising boat on the ability to go upwind makes no sense to me and I would say, no sense to the boat builders and naval architects and that's why you don't find them on the market, unless they are cruiser racers and therefore intended to race upwind.
&#8230;.


kevlarpirate said:


> *As for a definition of what comfort really is, that is subjective*. ...My Ericson 46 is very observably more comfortable than the SC50.
> &#8230;but again, if you were to interview crew after the SC sailed a circle around us I would be willing to bet the SC crew never even considered discomfort as an issue.
> kev


Well, it seems that I am not the only one that considers the relative comfort as a tradeoff and not an absolute item . And if you will let those guys chose between both boats for going on extensive cruising (providing both have similar interiors) I believe most of them would chose the fast and more modern boat.

I agree with you (finally ) on the subjectivity of the definition of comfort and what I have said in the beginning of this thread seems to go accordingly:

"The tastes of different sailors about the kind of sea motion they prefer, varies a lot. What is comfortable to you can be just boring and devoid of any sailing pleasure to another cruising sailor.

The type of comfort motion you like is a very personal thing, and varies as much as the different kind of cruising boats that are suitable to do Ocean passages, from the relatively heavy boats that you favor to the fast cruising racers, or Open type boats

I have owned a heavy displacement boat and I have owned a light displacement boat. I do prefer the motion of the light boat, not in all situations but on almost all of them. You have seen that on this thread I am not the only one that thinks that way. That doesn't mean I am right. There is not right or wrong here. Sailors should try both kinds of boats to see the difference in type of motion and to make a personal choice."

Saying otherwise, and going with your mass theory as the absolute panacea for comfort, would be implying that multihulls are less comfortable than monohulls and that seems a quite extraordinary statement considering the huge growth in popularity of monohulls among cruisers.

*Ted Brewer*, the one that created that comfort ratio formula also agrees with you on the subjectivity of comfort (and sea motion). He says:

"Nor will one human stomach keep down what another stomach will handle with relish, or with mustard and pickles for that matter! 

*It is all relative*."

Regards

Paulo


----------



## seabreeze_97

I have to ask. Any of you ever seen an old-style metronome? It has this metal rod, weighted at the bottom. It also has a weight on the rod and it slides the length of the rod. The rod wiggles back-and-forth rapidly if the weight is low on the rod, but as you move that weight up, the rod moves more slowly. Hmmmm. Isn't it neat how that so neatly parallels a sailboat? Maybe you should re-think that whole 500lb mast example Jeff.


----------



## PCP

seabreeze_97 said:


> I have to ask. Any of you ever seen an old-style metronome? It has this metal rod, weighted at the bottom. It also has a weight on the rod and it slides the length of the rod. The rod wiggles back-and-forth rapidly if the weight is low on the rod, but as you move that weight up, the rod moves more slowly. Hmmmm. Isn't it neat how that so neatly parallels a sailboat? Maybe you should re-think that whole 500lb mast example Jeff.


That's a good example. I have found one on line that is similar to a boat with a bulbed keel. You cam make it longer or shorter

FREE METRONOME SOFTWARE - Best Metronome .com

But you have to consider that you have two weights. One on the top, other on the bottom, like a boat with a fin bulbed keel. You are not only putting the weight up but you are also increasing the lenght of the keel.

Regards

Paulo


----------



## kevlarpirate

Paulo, I am not here to converse with you . These long winded exchanges are not productive. Anyone reading my statements has the right to do their own due diligence to and I suggest they do. 

I am here only to:
debunk any statements which do not follow laws of physics
debunk false marketing claims.
debunk false opinions 

To support my positions I reference facts, statistics and personal experience.
Anyone who has questions can ask for further explanation.
It has nothing to do with ego, just knowledge.

I read your very long post and several conclusions you made were exactly the opposite of what I stated. I will not comment as to how you may have drawn the wrong conclusion. 
One thing I will clarify is in reference to interior noise is that created by flat “zero dead rise transoms slapping and slamming all night long at anchor. It is more a design issue , and as for cored vs: solid hulls and noise,
It is a thickness issue. However, high modulus materials have higher acoustic velocities , no magic there, and the thinner they are , the more sound transmitted.

My posts are all consistent, there is absolutely nothing confusing about my statements , they are can all backed by references, and vetted by any and all readers willing to do some researching of their own. 

Good luck with your future boat


----------



## kevlarpirate

I have just come across some very well researched reading 
Technical Articles

the main page has been taken down , but the individuals are still available.
still looking but the author may be John Holtrop.

judging by his style and terminology he is obviously technically well versed.
He uses the correct words in the proper flow.

I strongly suggest reading "Dynamic Stability" to the letter and making a hard copy in case the page gets taken down. Pay particular attention to moment of inertia varies as radius squared , not just radius. this is why moment of inertia 
is dominant over CG by lengthening the "roll over" response time.


----------



## Jeff_H

Sorry to have been missing in action here. I am also sorry but this is a long one.

Let me see if I can address some of the points which have been raised so far. To begin with, I thought that the technical articles posted by Kev were interesting, but in many ways struck me as an oversimplification. That said, sometimes simplification is necessary to get key points across. 

Some things that we do appear to agree on, is that static stability in and of itself only tells part of the story, and frankly a pretty small part when it comes to motion comfort or predicting whether a particular boat will be likely to capsize. I think that we agree that dynamic stability is a critical predictor of the likelihood of a capsize and of the motion comfort of the boat.

I think we all agree that mass is a major component in the behavior of a boat, but we still seem to have a bit of a disagreement in sole or major significance. I think that we all agree with the idea that in terms of motion comfort that it is the range of motion (wider angles or larger amounts of movement), and change in the rate of speed of that motion (the accelleration and deaccelleration of a boat through all ranges of motion) that really dictates the motion comfort of any specific boat. 

From a physics standpoint, I don't think any of us disagree with the previously posted equation A= F/m. And so I believe that we all agree that mass plays an important role here. 

But where we seem to still have a gulf is the issue of how much of a role mitigating the accellerating- deaccelelrating forces play and and the signifigance of hull form and weight distribution on the amount of force that an individual boat encounters. And it is here that I think that Paulo and I are in agreement, that through careful decisions about weight distribution and hull form the forces experienced by the boat can be reduced so that a boat of lesser mass may still have a better motion characteristics. This is not to say all lighter weight boats will have a better motion, just that it is possible for a properly designed boat to have better seakeeping and seakindliness behavior than a heavier boat. 

I still think that making the case will still come down to the physics so I would like to take a specific case, which is the one that Seabreeze 97 refers to, which has to do with the impact of an increased moment of inertia on the speed of harmonic motion. I would think that we are all in agreemeent that as the weight on a metronome is moved away from the access of rotation, the speed of rotation will be slower for a given fixed input force (The spring on the escapement mechanism). This in effect is a simple pendulum turned upside down. 

If we apply this principle to motion comfort, we can look at two cases and see how the placement of the weight impacts the rotational motion of the boat. Lets look at two boats with equal height masts and equal depth and profile keels, and equal hull shapes. But one of these boats is constructed conventionally and the other with higher tech construction techniques. For the sake of discussion let us assume that that the low tech boat has the same 40 mast as the high tech boat, and for the sake of discussion, we put a 100 lb weight at the top of its mast. That weight would incease the roll moment of interia by 160,000 pound-feet squared (100 lbs x 40 ft x 40ft) and as Seabreeze points out, reduce the roll rate of the boat. The other boat does not have the weight at the top of the mast but neigher does it have the teak decks, or heavy teak interior, or a hull liner, or marble counter tops. Instead it it has a 3,300 lb bulb in the bottom of its keel, the center of gravity of that bulb being 7 feet below the roll center of that boat. In this case we have 3,300lb x 7 ft x 7 ft or an increase in roll moment of inertia of 161,700 pound-feet squared, which is similar to the increase in the moment of inertia for the 100 lb weight at the mast head. 

I think that we would all agree that both should have a slower harmonic motion than an equal weight boat that did not have either the weight at the mast or bulb at the bottom of the keel. But despite the fact that these boats have equal roll moments of inertia, I suggest that the behavior of the boat with the weight at its masthead as compared to the boat with the bulb will be extremely different in a seaway. 

If we look at mechanics of a boat lying beam to the waves and rolling in steep seaway, 1. there will be a rotational moment that is generated by the change in angle of plane of the wave face acting against the form stability of the boat, and 2. another rotational moment that comes from sheer of the surface of the wave acting on the underbody of the boat that results from the difference in the speed of the water at the surface which is moving faster relative to the water deeper in the wave, and 3. a third rotational moment that comes from gravity acting on the boat causing it to want to slide down the inclined plane of the wave and but that slide is being resisted by the keel creating a moment between the center of actual resistance and the center of the momentum of the boat. 

In our example of the two boats, since they have the same hull, weight and underbody profile, it would suggest that they will feel a similar roll inducing moment due to moment #1 and moment #2. 

But when we look at roll inducing moment #3, in this case the boat with the weight at the top of its mast wil have a higher vertical center of gravity and so the lever arm between the force couple (lateral resistance and center of gravity) will be longer creating a greater rotational force, and since both boats have an equal roll moment of inertia, there will be a faster roll rate for the boat with the mast weight than the keel weight. 

But also, if we continue to look at the rotational moments acting on the boats, in the case of the boat with the keel weight, the weight of the keel is acting in couple with the center of buoyancy creating a moment trying to right the boat vs. the weight at the top of the mast, which is also creating a couple with the center of buoyancy but one trying to overturn the boat, and so with equal inertia would tend to further increase the roll rate of the boat with mast weight. 

If we think then of these two boats sliding down the face of the wave an into the trough, when they hit the bottom of the wave, the boats being of equal weight and profile will hit the bottom of the wave moving at the same lateral velocity, but the boat with the mast weight will hit with a greater rotational speed. 

If we look at the forces felt by the crew on the boat, we would need to look at the rate of deacceleration. As I assume that we would agree upon, the force of deaccelleration will be proportionate to the change in speed, and the distance/time over, which that change of speed occurs. To some extent we do not have enough information, but in a general sense, boats in principle would experience an equal form stability righting moment at the bottom of the wave if they were at an equal heel angle. 

But since the boat with the mast weight has a greater rotational speed, it will actually have a greater heel angle at the bottom of the wave. In theory this greater heel angle would be result in a higher rate of side motion since the keel will have rotated out of the water flow but we can ignore that for a moment. 

Since the boat with the mast weight has a greater rotational speed at the trough and it will need experience a greater change in speed as it flattens out to begin its climb. That greater speed will create a greater momentum. Assuming an equal form drive righting moment for both boats, this greater momentum relative to righting moment will result in the boat with the mast weight having a higher heel angle at the time that the boat stops moving in the trough and begins rotate back to level. This greater momentum would also generate a greater impact force which would be felt by the crew as well. In other words the boat with the mast weight would likely experience a less comfortable motion having some mix of greater impact force and a larger roll angle experienced by the crew. 

By the same token, looking at likelihood of a capsize, as has been discussed earlier, as boats heel there is a point of maximum righting moment atfer which righting moment decreases. The amount of that maximum righting moment and the speed at which it decreases is mostly dependant on the hull/cabin shape and weight distribution. 

Continuing our example, the boat with the mast weight will be at a higher angle of heel when it impacts the trough of the wave. it will also have a reduced limit of positive stability that would result from having a higher vertical center of gravity as compared to the boat with the keel weight. So you have a boat that is rotating at a higher speed, hitting the bottom of the wave at a larger heel angle, that has a smaller LPS, and a more rapid loss in righting moment as it approaches its LPS. 

I would think that we would all agree that assuming the two boats in our example have equal moments of inertia, the boat with the mast weight would be more likely to capsize than the boat with the keel weight. 

I would think that this example provides one small case where weight distribution can be shown to be a significant determinant in both motion comfort and the likelihood of capsize. 

Getting back to the original topic, I hope that we can agree that at least in this case, since the Capsize Screen Formula and the Motion Comfort Index lack any information about the weight distribution of these boats, it would seem to provide no useful information about which of these two boats would be more comfortable or less likely to capsize. 

And assuming that we agree on the physics of the above example, I would assume that this satisfactorily explains the physics of the example that I cited earlier regarding placing a weight on the mast of a boat relative to these two dangerously useless formulas. 

Respectfully,
Jeff


----------



## kevlarpirate

Jeff. These issues are not that convoluted

One issue I see is perhaps you are not treating statics and dynamics as separate problems , you seem to be comingeling them in one unduly complex thought. 
Now don’t misunderstand me, What I am saying is that we need to analyze them individually. then combine later.

The static curve is a trivial concept . Everyone reading this can very easily find articles which describe it thoroughly. And of course , we want to have a high LPS. and minimum P/S ratios. The table of LPS minimums for all boat lengths to qualify for offshore racing categories are also readily available.

Dealing with moment of inertia , the way you need to think of it is in the transient sense.
In the case of a capsizing wave , that event is over in a just few seconds.
Refer to my prior post for that link. the section on dynamics It makes it very clear. 

Also, the rotational acceleration rate is a function of the systems “total”moment of inertia, therefore it does not matter where the individual moments comes from. 

Let me illustrate. Think of a holding a wagon wheel with your hand and your arm is out stretched horizontally Then rotate the wheel forward and reverse. 
The torque needed to overcome the moment of inertia is independent of whether 
There are 3 heavier spokes or 10 lighter weight spokes, any number of spokes for that matter , as long as the individual moments combine to equal the total moment of the original system.

When a wave rotates your boat, think of it as a two spoke wheel, 
The next step is to write a mathematical expression to describe that. , ( you don’t have to, it has been done a long time ago)


Probably the best point I can make is that all this work has been done and is very well referenced and explained. It is there for free on many websites and in books. I have pointed out several. 

The book; Desirable and Undesirable Characteristics for Offshore Yachts 
Is very thorough and easy to follow. Start around page 70.


One last note , you continue to stress CG position. We all want our CG’s to be low
But the point is , and this has been proven in the real world and tank testing that 
substantial vertical movements in vertical position of CG do not effect dynamic behavior that much.. The most substantial change we can make is removing the mast, and we find rollover frequency increases, not decreases. 

Counter intuitive , don’t you agree? Anyway , those old boys actually did know what they were talking about with the capsize screening ratios.
It's in the physics

kev


----------



## kevlarpirate

ignore min P/S ratio . we want minimum inverted area (vs: positive area)


----------



## Jeff_H

Kev,

As I see it, we have agreed that we would discuss the physics of motion comfort and likelihood of capsize as a way of exploring the original topic. Like any other discussion based in science on the behavior of a vessel under way, the only way to fairly analyze what is happening is to break the forces into their various components and from those component parts build "the wheel" that explains how a given boat is likely to behave in a given condition. 

I also suggest that there is no way to comprehensively discuss the physics behind the behavior of a boat without looking at both the dynamic and static forces at play. 

For example, we cannot discuss something seemingly as simple as drag without considering the dynamic forces (wave making, induced drag due to tip vortices, inter-planar turbulence, surface wave affects and so on), as well as, the more static conditions such as frictional drag. 

I do not see how we can have a meaningful discussion of the mechanics of motion and capsize with breaking various components that impact motion or capsize screening into its basic parts. Even the model testing that suggested that a boat is more likely to capsize without its mast is understandable when broken into its various parts. But it is also important to look at the full range of testing. If you look at the plots in the test repost, starting with no mast and adding rigging weight initially reduced the likelihood of a capsize, but at some point adding mast weight actually increases the likelihood of a capsize. 

Just for the record, I am very familiar with "Desirable and Undesirable Characteristics for Offshore Yachts". It does a very nice job of explaning the thinking of that era. But even John Rousmaniere, has told me and posted here in prior discussions that this was the best thinking of that era, but that we have a much better understanding of these issues than we had when Desirable and Undesirable Characteristics for Offshore Yachts was published nearly 30 years ago, and that modern designer have learned the lessons of that era and have designed boats that have responded well to those lessons. 

Similarly, in conversations that I have had a SNAME and American Yacht and Small boat symposia, some of the folks who worked on the Capsize Screen Formula have have told me that in the wake of the Fastnet, the capsize screen formula was written quickly in order to get into place some kind of rule of thumb about the likelihood of a capsize. It was meant as a quick first screening based on the types of boats that existed at the time.

Most yacht designers that I have spoken to about the CSF and MCI dismiss them as being a very poor indicators of how a yacht will perform in rough conditions and useless in evaluating designs that have taken the lessons of the Post Fastnet era and applied them to newer designs. Even Brewer has said he developed the MCI as a tongue in cheek index and was surprised that it caught on. 

But of course, those kinds of statements do not address the physics of the situation any more than "those old boys actually did know what they were talking about with the capsize screening ratios."  

Respectfully,
Jeff


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## cormeum

> But when we look at roll inducing moment #3, in this case the boat with the weight at the top of its mast wil have a higher vertical center of gravity and so the lever arm between the force couple (lateral resistance and center of gravity) will be longer creating a greater rotational force, and since both boats have an equal roll moment of inertia, there will be a faster roll rate for the boat with the mast weight than the keel weight.


The amplitude would be greater but the rate would be slower. The moments of inertia are resistive to changes in motion. So a high I(r) would reduce the rotational acceleration along the vector of the force applied. You are correct in assuming that having a weight at the end of the mast would induce a greater F(g) but that would only go as the sine of the angle between the mast and g. For a same total I(r) the acceleration is the same along an axis but the amplitudes will be different in the situation you describe since the contribution of the weight at the top of the mast is above the axis of rotation and so adds to the force (g) displacing the object from vertical. 
In a single impulse situation (t of the applied force is small compared to the oscillation period), a higher I(r) will induce less amplitude and a slower acceleration than low I(r)- all other things being equal.


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## Jeff_H

cormeum said:


> The amplitude would be greater but the rate would be slower. The moments of inertia are resistive to changes in motion. So a high I(r) would reduce the rotational acceleration along the vector of the force applied.
> 
> You are correct in assuming that having a weight at the end of the mast would induce a greater F(g) but that would only go as the sine of the angle between the mast and g. For a same total I(r) the acceleration is the same along an axis but the amplitudes will be different in the situation you describe since the contribution of the weight at the top of the mast is above the axis of rotation and so adds to the force (g) displacing the object from vertical.
> In a single impulse situation (t of the applied force is small compared to the oscillation period), a higher I(r) will induce less amplitude and a slower acceleration than low I(r)- all other things being equal.


I think that we are basically in agreement. I am not sure whether you had noticed that in the example, both boats had a roughly equal roll moment of inertia (Ir), which was based on one boat having a smaller weight at its masthead as compared to the other boat with a big weight at the bottom of the keel. In essense, they would both resist acceleration due to an equal roll moment equally, but the weight at the top of the mast would mean a greater roll moment on the mast weight boat than on the keel weight boat and so would also have a faster roll rate.

What I have not touched on in this discussion is that in short to medium duration repetative waves, increasing roll moment of inertia will tend to cause the roll of the vessel to be out of phase with the wave train. In larger waves, this can cause the vessel to have a greater impact at the crest and troughs which can mean more rotational force being applied to the vessel. In the case of the mast weighted boat, this would be exacerbated by the higher rotation velocity relative to keel weight.

Jeff


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## cormeum

Jeff_H said:


> I think that we are in agreement. In the example, both boats had a roughly equal roll moment of inertia (Ir), which was based on one boat having a smaller weight at its masthead as compared to the other boat with a big weight at the bottom of the keel. In essense, they would both resist acceleration due to an equal roll moment equally, but the weight at the top of the mast would mean a greater roll moment on the mast weight boat than on the keel weight boat and so would also have a faster roll rate.
> 
> Jeff


Since the moments of inertia are the same, the accelerations would be the same for both. Intuitively, I'd think the "roll rate" would be slower since the masthead boat would swing through a larger arc (bigger theta)- since the a's are the same, t would have to be larger to account for the larger amplitude.. The amplitude of the roll would be different due to the location of the mass being below the roll axis in the keel situation, thereby resisting gravity trying to tilt the boat and greater for the masthead example since the mass would be applying a force in the same direction as the displacement from vertical when the boat is heeled.

I resist using "moments" for anything else than inertial properties of objects because it's easy to confuse things when using words instead of math. Both these situations, of course, ignore damping.


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## PCP

kevlarpirate said:


> ...Catamarans when caught in a storm are notoriously dangerous by design as are light weight sport boats.
> 
> ....I am writing here for other readers who may be new to this and are doing internet searches to educate themselves. I have plenty of non biased knowledge to share. I will be monitoring posts to detect bias and misinformation .


About non biased and misinformation, I found this statment particularly...odd? Strange?, or should I say biased?

About this *:"Catamarans when caught in a storm are notoriously dangerous by design"* - let me tell you that one of the things tank testing have showed is that catamarans, particularly cruising cats, are many times harder to capsize than a monohull. They have a huge stability and that statement of yours is not supported by reality.

About this: *..."(light weight sport boats) when caught in a storm are notoriously dangerous by design".* I suppose you consider a Class 40 cruiser/racer a light boat. He weighs only 4500 kg, for 12m length. Everybody knows that this boat, for its size, is one of the safest boats around. After many Transats (with lots of boats, solo crewed), including circumnavigation races, they have an impeccable safety record. And you can bet they have already got their share of storms.

Of course I am not even talking about the Minis, even with more Transats on their log (thousands), sailing sometimes with winds over 50k and huge seas, also with an impeccable safety record (these are 26ft with a 1000kg displacement).

Your statment is so obviously biased that I refuse to discuss this issue further, and I have to say that I am a little worried when you say:* "I will be monitoring posts to detect bias and misinformation."*

Regards

Paulo


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## kevlarpirate

To understand moment of inertia , it will be very helpful to disassociate it from any other system with other forces acting upon it. 

Think of the system as masses on the end of weightless sticks. Then when understood, and using proper terminology, and understanding the math apply it to a more complex system.

Paulo, a catamarans stability curve has more area under the curve than above the curve, due to having a mast. Therefore the design is more happy to be upside down than right side up, meaning the system requires more energy to right it than the original energy to invert it. The only feature which makes a cat safe is it's size relative to waves of the ocean state it is sailing in, providing of course it does not break up.

Please reference appropriate literature which explains this. 

as for other literature available , I suggest you read Principles of Offshore Design Larrson and Eliasson . chapters on stability, it is all there , fully explained , no need to fight here


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## PCP

kevlarpirate said:


> Paulo, a catamarans stability curve has more area under the curve than above the curve, due to having a mast. Therefore the design is more happy to be upside down than right side up, meaning the system requires more energy to right it than the original energy to invert it. The only feature which makes a cat safe is it's size relative to waves of the ocean state it is sailing in, providing of course it does not break up.
> 
> Please reference appropriate literature which explains this.
> 
> as for other literature available , I suggest you read Principles of Offshore Design Larrson and Eliasson . chapters on stability, it is all there , fully explained , no need to fight here


Kev, Jeff had posted this about that book, I mean Priciples of Offshore Design. I agree with him.



Jeff_H said:


> ...Just for the record, I am very familiar with "Desirable and Undesirable Characteristics for Offshore Yachts". It does a very nice job of explaning the thinking of that era. But even John Rousmaniere, has told me and posted here in prior discussions that this was the best thinking of that era, but that we have a much better understanding of these issues than we had when Desirable and Undesirable Characteristics for Offshore Yachts was published nearly 30 years ago, and that modern designer have learned the lessons of that era and have designed boats that have responded well to those lessons.
> Jeff


You should read more up to date information on stability. The information on that book is not specific to Cats and anyway, Cruising cats were just new born babies when the book was written. At the time there was no sufficient or reliable information about them.

You are right, a Cat has about the same stability in the normal position or upside down. The mast is of no relevance, because it breaks' when the boat capsizes. But you are missing the point, in what concerns cat's stability:


PCP said:


> ...tank testing have showed that catamarans, particularly cruising cats, *are many times harder to capsize than a monohull*. Paulo


Of course, this could not be true, if that theory of yours, that puts as critical factors to prevent capsizing, mass and a big moment of inertia, was true. Cats are the sailboats with less mass and sailboats with a low moment of inertia (but with a huge stability). But as this is true, as has been demonstrated on extensive tank testing, than, your theory.....

Regarding Cats, stability and Capsizing I would recommend to you," Model tests to study capsize and stability of sailing multihulls" by Barry Deakin. I believe it is from 2003.

I can quote a small part to you:

*"Only one reliable account has been found of a catamaran capsize due to a beam encounter with a breaking wave. This was a 9m yacht wich encountered a wave about 9m high, with a breaking crest. The low incidence of such casualties is perhaps due to the low probability of encountering a wave of sufficient size, on the beam&#8230;when it breaks.*

*The much greater incidence of monohuls capsizes may be because they&#8230;require smaller waves."*

Regards

Paulo


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## kevlarpirate

Paulo, To me, you don't sound like you read that book and chapters on stability.
How long ago did Jeff make reference to it?

More specifically, catamaran stability is nothing new. One problem you are having is thinking new knowledge is replacing laws of physics. this is simply not true.
As for catamarans, I have capsized countless times not by a beam sea but 
by getting in the danger zone and not being able to recover because 
you can't let the main out fast enough. Another scenario is digging the leeward bow in , which swings the apparent wind rearward (as the boat slows and also turns down) and then over you go.

My point about stability was that once you are over , there is no way to re invert to upright. Even the worst static curve monohull has a chance of inverting back to upright. The point is that cats are vulnerable to capsize. However that capsize occurs is not the issue, the issue is they do.

In 1999 Transpac i recall Double Bullet , 76 feet long, capsized in 8-10 foot seas,
Also included here is a link to another disaster, this was a 50 foot cat.

Perhaps with your knowledge, you could forward a theory on how these events happened. I will be interested to read it, thank you in advance

TRANSPAC 99 - Press Release 7-07-99 - Double Bullet II capsizes, 6 crew rescued by helicopter

Catamaran washes ashore, crew missing | KATU.com - Breaking News, Sports, Traffic and Weather - Portland, Oregon | News


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## seabreeze_97

PCP said:


> That's a good example. I have found one on line that is similar to a boat with a bulbed keel. You cam make it longer or shorter
> 
> FREE METRONOME SOFTWARE - Best Metronome .com
> 
> But you have to consider that you have two weights. One on the top, other on the bottom, like a boat with a fin bulbed keel. You are not only putting the weight up but you are also increasing the lenght of the keel.
> 
> Regards
> 
> Paulo


It was my attempt to address the basic motion comfort as handled by Jeff where he draws on the example of two identical boats, one with, and one without a 500lb mast-end weight. He states the motion comfort would be adversely affected. A simple metronome disproves that statement. 
Having identical boats, but one with more weight aloft, the other with considerably more weight down under can yield two boats that have the same motion comfort. Sure, but not everyone wants a 6-foot 4-ton bulb keel. Obviously, different construction and weight of the hulls would require different keel and rig dimensions to achieve the same motion comfort numbers, if that were the goal. In the racer's world, with unlimited funding, I can see where some high-tech construction and low slung, heavy bulb would be preferred, but then is motion comfort really the priority? In the cruiser world, why have an inconveniently long keel loaded with expensive lead when a few extra feet of mast (or a slightly heavier and I would wager considerably less costly mast) would achieve the same goal?


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## blt2ski

Seabreeze,

The keel depth, will depend upon where you/cruise sail. Here in Puget Sound where I am, an 8' keel is not a big deal, as usually you are sailing in 600+ feet of water. Even towards the shore, you can be in 100-200' just yds off shore. I have seen pics of boats with the bow touching a cliff, with 300' below them, to 600' above them! 

I am sure if on the east coast of the US< shoal draft boats seem to be more the norm, or need. So extra mast is nice. Or if in a low wind, deeper keel, taller mast to catch the breezes is also nice. now you have both going on, it taller mast, deeper keel, potential to use less lead as the keel goes deeper, vs shallow and heavier, be it a bulb or no bulb........

Too many varibles to say one varible is the one and only key to this whole thing.

Just like the why did the two cats flip in above articles? the ocean racer, my swag is the boat had a hull lifted, mast broke, going to leeward, heeling cat more, Cat probably is an equal to an 80' Hobie cat with a tramplin between the hulls,Wind got beneath the lifted hull, blew on the tramp, over the boat went! or some equal to what I wrote. Not sure about the cruising cat, other than off the shore of Wa and Or that week or two previous, and after, were storm force winds with large seas. Maybe a rogue or two or three to take out the cat sidways.

Marty


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## PCP

seabreeze_97 said:


> ....Obviously, different construction and weight of the hulls would require different keel and rig dimensions to achieve the same motion comfort numbers, if that were the goal. In the racer's world, with unlimited funding, I can see where some high-tech construction and low slung, heavy bulb would be preferred, but then is motion comfort really the priority? In the cruiser world, why have an inconveniently long keel loaded with expensive lead when a few extra feet of mast (or a slightly heavier and I would wager considerably less costly mast) would achieve the same goal?




It seems to be an appealing proposition for cruisers, but don't you think that if it was that simple we would have on the market a type of boat with that characteristics'? 

Yes, a boat with a heavy mast, or, as Kev has proposed with a heavy weight on the top of the mast would have a slower movement (less acceleration) but if we just do only that, we would have an eventually comfortable but dangerous boat. The AVS point would be improperly low, the positive stability would be drastically reduced and the inverted stability would be increased. For compensating all these loses, you would have to add a lot of weight to your ballast, resulting in a slow and more expensive boat, a boat that would also need a bigger rig and bigger sails.

That´s why there is no such boat on the market.

Please read post 21 of this thread. I have explained what would have happen if we put a 500lb weight on top of the mast of a Tayana 37. Of course, you talk not of a big weight on top of the mast, but of a slightly heavier mast, but the principle remains the same. That's why all designers and builders are interested in lighter masts and not on heavier ones.

Regards

Paulo


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## Jeff_H

seabreeze_97 said:


> It was my attempt to address the basic motion comfort as handled by Jeff where he draws on the example of two identical boats, one with, and one without a 500lb mast-end weight. He states the motion comfort would be adversely affected. A simple metronome disproves that statement.
> Having identical boats, but one with more weight aloft, the other with considerably more weight down under can yield two boats that have the same motion comfort. Sure, but not everyone wants a 6-foot 4-ton bulb keel. Obviously, different construction and weight of the hulls would require different keel and rig dimensions to achieve the same motion comfort numbers, if that were the goal. In the racer's world, with unlimited funding, I can see where some high-tech construction and low slung, heavy bulb would be preferred, but then is motion comfort really the priority? In the cruiser world, why have an inconveniently long keel loaded with expensive lead when a few extra feet of mast (or a slightly heavier and I would wager considerably less costly mast) would achieve the same goal?


Seabreeze, If your read my explanation in post 89, you would see that even if the boat with the weight added to its mast and the boat with weight added to its keel had equal roll moments of intertia, the boat with the weight up its mast would have a quicker roll rate, through a wider angle and with harsher de-accelerations than than the boat with the weight on its keel.

Although the weight up the mast is larger than might be the norm, and the weight on the keel is heavier than might be the norm, in reality, boat builders have actually shifted their paradym, and are routinely using lighter weight rigging and spars and bulb keels as a way of improving motion comfort.

And while it may seem counter intuitive to think that designers of race boat are interested in motion, that is very far from the truth. Their motivation may not be making the crew's lives more comfortable, but years ago, designer identified motion as a major performance frontier. If a boat has reduced roll and pitch angles can be reduced, its roll rates slowed, and if it can be designed with softer transitions, and if its impact with waves can be reduced, the flow of air over the sails and the flow of water over the keel and rudder can be much more efficient.

To a great extent current IRC style racer/cruiser hullforms, with their fine bows, eliptical hull sections, folis designed to promote dampening, and so on, offer tremendous advantages in terms of motion comfort as well as performance.

These efforts at improved hull modeling and weight distribution have proven so succesful that conservativel cruising boat manufacturers such as Hallberg Rassey have adapted these advanced design concepts to their newer models.

Respectfully,
Jeff


----------



## PCP

kevlarpirate said:


> ...
> As for catamarans, I have capsized countless times not by a beam sea but by getting in the danger zone and not being able to recover because you can't let the main out fast enough. Another scenario is digging the leeward bow in , which swings the apparent wind rearward (as the boat slows and also turns down) and then over you go.
> 
> My point about stability was that once you are over , there is no way to re invert to upright. Even the worst static curve monohull has a chance of inverting back to upright. The point is that cats are vulnerable to capsize. However that capsize occurs is not the issue, the issue is they do.
> 
> In 1999 Transpac i recall Double Bullet , 76 feet long, capsized in 8-10 foot seas,
> 
> Also included here is a link to another disaster, this was a 50 foot cat.
> 
> Perhaps with your knowledge, you could forward a theory on how these events happened. I will be interested to read it, thank you in advance
> 
> TRANSPAC 99 - Press Release 7-07-99 - Double Bullet II capsizes, 6 crew rescued by helicopter
> Catamaran washes ashore, crew missing | KATU.com - Breaking News, Sports, Traffic and Weather - Portland, Oregon | News


I bet that you never had capsized a cruising cat and that are the ones we are talking about.

Let's put some order on this discussion:

You have said:

*"Catamarans when caught in a storm are notoriously dangerous by design"*

And it was regarding this that I have said, based on the extensive research and studies made by the technical group that was working for establishing safety standards for multihulls to be sold on the EC, that (and quoting Deakin)

*"Only one reliable account has been found of a catamaran capsize due to a beam encounter with a breaking wave. This was a 9m yacht wich encountered a wave about 9m high, with a breaking crest. The low incidence of such casualties is perhaps due to the low probability of encountering a wave of sufficient size, on the beam&#8230;when it breaks.*

*The much greater incidence of monohuls capsizes may be because they&#8230;require smaller waves."*

I can add also, that small cat (9m) was modified by the owner in a way that contributed to that capsize.

You were talking of* Cats in Storms*. In storms you have your sails down, or just have a very small sail, just for control and therefore what I have said remains valid. In a storm a cruising catamaran is a very safe boat and the possibilities of a capsize are many times smaller than the ones experienced by a similar sized monohull, so small that on all that research work (many years taken in consideration) they could only find one case and with a small cat (9m).

You are mixing small sports cats (hobbie cats), racing cats and cruising cats. We are talking about cruising boats and cruising cats.

Even cruising cats can, and have been capsized, but not (except that case) for only breaking waves. While monohulls cannot be capsized by just wind (but can be capsized by a breaking wave) Cats (with the sails up) can be capsized only by wind (but are extremely difficult to be capsized by a breaking wave).

Cruising cats have relatively small rigs and can have a lot of sails up with a lot of wind without having a capsizing risk, but that is true that you have to be a better sailor to sail on the limits a cat (with lots of wind), than to do that on a monohull. They are more sensitive to mistakes (if you are a daring sailor), and that is even more true in what regards racing a multihull.

A cruising cat is altogether a very safe boat. That's one of the reasons of its growing popularity among cruisers.

Regards

Paulo


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## Jeff_H

Paulo, 

While I am not one of those people who believe that multihulls are inherrently more dangerous than monohulls, I do think that it is an understatement to say that there has only been one recorded capsize due to waves of a cruising cat, no matter who says it. 

The reason that I say this is that my father's boat was hit by the mast of a cruising cat that was blown over in an anchorage. The facts of the matter are that my father and this cat were on moorings in a relatively open anchorage in the Bahamas when a front came through. There were a series of violent gusts and wind shifts. One of these had enough wind, at a steep enough angle to heel my father's heavy 42 footer as if under a full press of sail, and as it was descibed, the cruising cat actually lifted part way out of the water and was blown over. 

I know that a part of a multihull's defence mechanism is that a part of the force of a gust is dispersed through acceleration, and being on an anchor the cat could not accelerate, but I have think that capsize is still a very real possibility in large winds rather than the large seas required to capsize a properly designed mono-hull. In the end its all about what you fear most; losing your keel or being rolled and sinking, or ending up floating upside down. 

Jeff


----------



## PCP

Jeff_H said:


> ....
> And while it may seem counter intuitive to think that designers of race boat are interested in motion, that is very far from the truth. Their motivation may not be making the crew's lives more comfortable, but years ago, designer identified motion as a major performance frontier. If a boat has reduced roll and pitch angles can be reduced, its roll rates slowed, and if it can be designed with softer transitions, and if its impact with waves can be reduced, the flow of air over the sails and the flow of water over the keel and rudder can be much more efficient.
> 
> To a great extent current IRC style racer/cruiser hullforms, with their fine bows, eliptical hull sections, folis designed to promote dampening, and so on, offer tremendous advantages in terms of motion comfort as well as performance.
> 
> These efforts at improved hull modeling and weight distribution have proven so succesful that conservativel cruising boat manufacturers such as Hallberg Rassey have adapted these advanced design concepts to their newer models.
> 
> Jeff


Jeff,

That's true and that's a point that passes unnoticed by many.

The HS 372 is the best proof of that. That is a fantastic boat that has been acclaimed as one of overall best boats of the last years.

Hallberg-Rassy 372

Several years ago I had pointed that tendency on the design of cruising boats ( to follow the advances in hull shape coming from the racing boats) in another forum, particularly in what concerns relatively fine entries, large transoms and relatively deep bulb keels. That was just a tendency, today is almost the norm.

About the IRC rules, Yes, they have contributed to better boats, but that rule brought also small idiosyncrasies. For example, an A40, when is for racing in IRC has a different keel (shorter) that the one that is mounted when the boat is used for racing in an Open category (that one designed for pure efficiency). IRC also penalizes beam, so all boats tend to be designed not to perform on an absolute best, but to perform best accordingly to a set of rules, even if most of them make sense.

I believe that now the biggest influence on cruising boats comes from the Open boats. Some designers state that clearly (for instance, on the hull design of the Jeanneau 42I) other manufacturers and one's as conservative as Wauquiez, state that even more clearly (about its new boat):

*"The Opium design is directly derived from the Open 60's design and will satisfy all sailors that like to sail and to cruise fast and comfortably."*

Of course, this can be false, but what counts is that a respectable and conservative boat manufacturer is advertising such a boat for that purpose, and even more, is producing it. That would be unthinkable, some years ago.

http://www.wauquiez.com/presse/opium-39/pdf/brochure-Opium-39-EN.pdf

I am waiting for this boat's stability curve. When I have it, we will discuss the boat on this thread:

http://www.sailnet.com/forums/boat-review-purchase-forum/62341-interesting-sailboats-8.html

And I would like to have your participation .

Regards

Paulo


----------



## PCP

Jeff_H said:


> Paulo,





Jeff_H said:


> While I am not one of those people who believe that multihulls are inherrently more dangerous than monohulls, I do think that it is an understatement to say that there has only been one recorded capsize due to waves of a cruising cat, no matter who says it.
> 
> ...Jeff



Jeff, 
I, being a monohull sailor have the natural tendency to distrust multihulls and have to make an effort to accept credible hard information to try to form a non biased opinion about cat's safety.

The critical factor here is: *How accurate and credible is that information?*

The information that I have posted come from a specific research, a tank and wind tunnel study on multihulls capsize and stability. I believe the best there is. Deakin is a member of the Wolfson unit (Southampton University) and as you know, this is the most knowledgeable research group on Yacht capsize, with studies based on statistical research and tank analysis.

The statistics Deakin is using come from the Wolfson unit and regards the years from 1995 to 1965. They analyze 124 accidents (only cruising multihulls over 7m). 

Statistics deal with numbers and facts and establish trends and probabilities. They are not saying that a cat cannot be capsized only by a breaking wave, fact is that they have capsized them on the tank study. What they are saying is that from the 33 cats capsize reports they had, only one was due to a breaking wave.

They are also saying is that it takes a much bigger breaking wave to capsize a Cat, compared to a monohull (tank studies). They are saying (statistically based) that while breaking waves are the most common cause on a monohull capsize, they are not, on a multihull. Excess of Wind and sail (associated or not with waves, not necessarily breaking waves) are the most frequent cause on multihulls capsize.

As you know, they can make this comparison between monohulls and multihulls, on the size of breacking waves needed to capsize each type of boat, because they had made also tank tests about that, with monohulls (some years back).

Regarding that episode you are talking about, I doubt that the Cat would have capsized. They talk about a similar effect on tank testing, with the cats going very fast sideways, without capsizing. 

Regards

Paulo


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## kevlarpirate

jeff you say:

"you would see that even if the boat with the weight added to its mast and the boat with weight added to its keel had equal roll moments of intertia, the boat with the weight up its mast would have a quicker roll rate, through a wider angle and with harsher de-accelerations than than the boat with the weight on its keel. "

This statement is false, it violates moment of inertia. 
Total moment is the sum of the individual moments. Total moment 
is independent of positions of individual moments. (first year physics)

Also , designers lower mast weight to pull a better LPS number for offshore categories. As for comfort , it is decreased because accelerations increase

You say: "If a boat has reduced roll and pitch angles can be reduced, its roll rates slowed, and if it can be designed with softer transitions,"

You have it backwards: the only way to reduce pitch and roll angles
is to lower moment of inertia and mass which will increase accelerations

"the softer transitions and harsher" Please use appropriate technical terms. You are referring to accelerations here. These other terms you use can confuse the novice reader.

Also please site references for the wider angle and harsher decelerations.
In fact please show all your references in the future.. I have done so

Paulo: cruising cats have to depower to reduce capsize risk. The advertised 
advantage of cats is speed, this negates that claim.

Cats regularly capsize in less than storm conditions , typically by burying a lee bow
when fully powered up. data is out there. You may also research insurance claims multi vs:mono ...... 5 to 1 as it turns out , adjusted numbers.

here is an example ,, which did NOT lose it's mast as you claim they all do 
Reynolds Sailing Catamarans and multihulls, boat builders and dealers of sailboats specializing in catamarans. Current boats for sale is the trailerable R33 cat and R50 cat designed by boat designers Randy Reynolds and Morrelli and Melvin.

Also , you claim no boat can have heavy keel and mast 
You may reference a Valiant 40 designed by ......yes, Robert Perry 
A fine example of comfort and performance especially for cruising
I have sailed a Baba 40 and have proved this

My Bruce King Ericson 46 is even a better example: 32000 lbs dry.
16500 lbs lead in a 7.2 foot keel, and a 68 foot tall Sparcraft mast.

When you come upon a wave at 8 kts upwind , that wave is sliced in two
and white water left behind. the bow hardly rises. Now THAT'S comfort

Mass and moment of inertia rule! in two words: size matters


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## kevlarpirate

Here is a reference to a statement I made in reference to catamarans:
Catamaran Controversy

It is not my intention to bash catamarans. I simply respond to misinformation 
especially by manufacturers needing customers.

I respect that many competent sailors successfully sail cats, however those owners will exercise extra cautions in ocean states and wind conditions that the same level of sailor would not have to be concerned with sailing a mono hull in the same conditions.

Not all mono hulls are the same, some are just superior in developed sea states. more comfortable , more powerful, It is nothing terribly complicated
No laws of physics have changed, all boats are treated equal by the wind and sea. How those different boats respond covers a wide spectrum

Cruising cats get in trouble especially when loaded up with cruising gear
which drives the leeward hull lower. In this situation vital freeboard 
is reduced. The experienced skipper will be always aware of this and de-power. Cats need to be run light to preserve freeboard. This works against the concept of "cruising" catamaran.

Tank tests which show cats do well with beam seas is easily understandable
due to moment of inertia and that the width of the cat compared to the height of the wave is high.

Lying ahull could be the safest plan for a storm. however without a drogue, it would be very difficult to maintain the hulls parallel to the wave.

We all know a breaking big sea is something to avoid at all costs, however, to imply that breaking beam seas are the only issue a cat sailor has to worry about is very misleading. To claim victory because cats do well in beam seas is simply disinformation.

Cats go over in benign conditions far more often than a beam on storm wave. Good sailors and catamaran delivery skippers know this well.
That's why they are delivered empty of everything but essentials.


----------



## JomsViking

> Lying ahull could be the safest plan for a storm. however without a drogue, it would be very difficult to maintain the hulls parallel to the wave.


Kevlar,
Lying ahull is very different from deploying a drogue, and the drogue is there to ensure that the hull is NEVER parallel to the waves, so while I won't argue with your physics, your understanding of heavy weather survival techniques sound questionable - at least to me.
Also many well-known long distance cruisers, such as the Harries (In-Depth Discussion of Sailboat Refit, Part I|Offshore Sailboat Voyaging|Attainable Adventure Cruising) prefer lighter spars, so practical experience also seems to support Jeff and Paulo.
All IMnsHO.
/Joms


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## PCP

kevlarpirate said:


> ]Paulo: cruising cats have to depower to reduce capsize risk. The advertised advantage of cats is speed, this negates that claim.


These kind of statments are becoming typical&#8230;I don't understand what you mean, I have never said otherwise.

A cruising monohull is not much slower than the average cruising cat and can point better into the wind. But what has this to do with your claim, the one I have contested? I mean, this one:
*"Catamarans when caught in a storm are notoriously dangerous by design"*

I am not defending cats against monohulls (neither the opposite).



kevlarpirate said:


> Cats regularly capsize in less than storm conditions , typically by burying a lee bow when fully powered up. data is out there. You may also research insurance claims multi vs:mono ...... 5 to 1 as it turns out , adjusted numbers.


Yes, of course, every week or so.

Your claim, the one I disagree was:

*"Catamarans when caught in a storm are notoriously dangerous by design"*

What have less than stormy conditions (normal muscular conditions) have to do with that? What I have said has to do with cats in storms. That was your point.

I have said, quoting an authority in the matter :

*"Only one reliable account has been found of a catamaran capsize due to a beam encounter with a breaking wave. This was a 9m yacht which encountered a wave about 9m high, with a breaking crest. The low incidence of such casualties is perhaps due to the low probability of encountering a wave of sufficient size, on the beam&#8230;when it breaks.*

*The much greater incidence of monohuls capsizes may be because they&#8230;require smaller waves."*

"You were talking of Cats in Storms. In storms you have your sails down, or just have a very small sail, just for control and therefore what I have said remains valid. In a storm a cruising catamaran is a very safe boat and the possibilities of a capsize are many times smaller than the ones experienced by a similar sized monohull."

Kev,* it is about Cats in Storms*, not about cruising cats capsizing for excess of sail to the prevailing normal but muscular conditions.

I have said that cats can be capsized:

".. cruising cats can, and have been capsized, but not (except that case) for only breaking waves. While monohulls cannot be capsized by just wind (but can be capsized by a breaking wave) Cats (with the sails up) can be capsized only by wind (but are extremely difficult to be capsized by a breaking wave). 

Cruising cats have relatively small rigs and can have a lot of sails up with a lot of wind without having a capsizing risk, but that is true that you have to be a better sailor to sail on the limits a cat (with lots of wind), than to do that on a monohull. They are more sensitive to mistakes (if you are a daring sailor), and that is even more true in what regards racing a multihull. "

This means that actually, it is more probable an irresponsible sailor capsize a cruising cat in normal but muscular sailing conditions, than in a storm. In a storm even an irresponsible sailor will not be tempted to leave too much sail up.

About insurance claims, are you sure you are not mixing small sport cats with cruising cats? I don't understand how that can be, because I don't think cruising cats insurance is more expensive than monohull insurance. Of course, I can check it out, but perhaps members of this forum with a cat, can give us a help.



kevlarpirate said:


> here is an example ,, which did NOT lose it's mast as you claim they all do


That is also typical. I didn't say that the mast always breaks. I have said:

"You are right, a Cat has about the same stability in the normal position or upside down. The mast is of no relevance, because it breaks when the boat capsizes."

That means that normally it breaks (not that it breaks all the times), but I fail to see the relevance since *I have said that Cats have about the same stability in normal position or upside down*. Of course, I could have said that the big cabin contributes for a lesser inverted stability. But what would be the point? That would not change the fact that the chances of righting the boat are so slim as the chances to have it capsized.



kevlarpirate said:


> Also , you claim no boat can have heavy keel and mast You may reference a Valiant 40 designed by ......yes, Robert Perry A fine example of comfort and performance especially for cruising
> I have sailed a Baba 40 and have proved this


Again, you misquoted me: I never have said that a boat cannot have a heavy keel and mast. I have said this:

"That´s why there is no such boat on the market&#8230;&#8230; That's why all designers and builders are interested in lighter masts and not on heavier ones."

I believe that Valiant still manufactures a 42 ft, but the design of that boat is 35 years old. I was obviously talking about today's boat designs.

Anyway the Vailant has an aluminum extrusion mast, not a wooden mast, a steel mast or a mast purposely heavy, with lead inside or anything funny like that.

The funny thing is that the Valiant was on its time a brilliant and innovative boat, a fast boat: It was known as the first performance cruiser. It was a very light cruising boat, for its time.



kevlarpirate said:


> ]in two words: size matters


I agree, size (length) matters.

Seriously, I understand your notion of comfort and I have nothing against it, but it seems that you are incapable of seeing that mass and moment of inertia are not the only elements that contribute to define a boat motion on the water and that the notion each person has about what a comfortable boat motion is varies, from person to person. I am not the only one saying that. The one that has created the comfort formula, Ted Brewer was the first to say that.

Regards

Paulo


----------



## PCP

For the ones that would like to have what I consider a fair and knowledgeable opinion about Cats, there is an excelent article, here on the sailnet, by Jonh Kretschmer, a multihull sailor with more than 8000 miles delivering cats.

He says:

*"The two top misconceptions about cruising cats are: (1) they are significantly faster than a comparable-length monohull, and (2) they are prone to capsizing and are dangerous offshore."*

http://www.sailnet.com/forums/buying-boat-articles/19386-reality-check-cruising-catamarans.html

Regards

Paulo


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## kevlarpirate

Viking , I am reasonably familiar with drogue theory and procedure and also the various drogues available, including the Jordan series drogue.

My point is that the cat may , and I say may have it's best defense
against big sea if it lies exactly parallel, and in that case , unlike standard 
deployment off a boats quarter, the drogue would be deployed exactly off the beam. 

This is just a thought , that's all. My thinking is that in a zero headway
beam on attitude, the downwind hull , if kept parallel , would provide the greatest boyancy to keep from submerging. If it were not parallel
and the boat was able to gain headway, it could bury an end (bow or stern) 
and dig in and roll. Again , just a thought 
I will read the blog you sent 

Paulo, your posts are soooooo long, I will have to read it later

Kev


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## kevlarpirate

Paulo got delayed for a bit .
My statement about being notoriously dangerous in a storm sea 
also included the high wind component. 

If you were in a storm and say has a storm sail up and at least trying to 
make forward progress , or for that matter running off on bare poles, 
you still would be worried that after 15 to 20 degrees of heel you are in the danger zone on your static curve.

So if your boat were tipped (not even heeled) 
on the face of a wave by 15 or so degrees , you are still angled 15 
degrees even though the face of the wave is 15 degrees also.

Yes , you are de-powered so as to keep both hulls in the water, but the 
face of the wave is angled and you are parallel to it 

for every degree past that , the torque needed to heel more, that torque is diminishing at a rapid rate. I know you know this so forgive me for my long winded explanation. 

My point is , you can't tolerate any more help from wind in sails or
rigging resistance. you have to stay flat. 

As for comfort , the only other passive contributor would be velocity
and the available kinetic energy, however this would involve much greater speed . I doubt if the human senses could resolve that in a half knot difference upwind. 
any thing I have not addressed tell me. Kev now I have to run


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## Paul_L

kevlarpirate said:


> ......
> As for comfort , the only other passive contributor would be velocity
> and the available kinetic energy, however this would involve much greater speed . I doubt if the human senses could resolve that in a half knot difference upwind.
> any thing I have not addressed tell me. Kev now I have to run


It really seems silly to discuss comfort in terms of a survival storm. No matter what cruising size boat you are in it is going to be very uncomfortable.

Paul L


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## cormeum

Jeff_H said:


> Seabreeze, If your read my explanation in post 89, you would see that even if the boat with the weight added to its mast and the boat with weight added to its keel had equal roll moments of intertia, the boat with the weight up its mast would have a quicker roll rate, through a wider angle and with harsher de-accelerations than than the boat with the weight on its keel.
> 
> Respectfully,
> Jeff


# 98 isn't your post, but anyway: larger amplitude of roll, slower rate, and equal accelerations at equal thetas.

To be fair, the construction you've been pitching is not realistic. 
Adding weight to the keel will increase the restoring force when the boat is heeled and delivers a faster roll rate and higher accelerations (We'll continue to consider this system undamped). The boat with the lesser stability (heavy stick)will have the easier motion since there is not as much available restoring force to swing the boat back to vertical. Less F, same M means less A. I think it was Froude that said that stability is what allows the sea to put a boat in motion. I think it's intuitive that a high righting force will provide high accelerations. 
Ultimate stability will of course be another consideration, but within reasonable parameters a big M (keel) at a fairly small r (keel depth) kicked slightly off center when upside down (small theta) will provide more restoring force than a heavy stick (still a comparitively small M) with a big r and the same deflection angle. Hull shape is more of the driver in that situation since the buoyancy force times its distance from the axis of rotation is what determines the necessary applied force to right the boat a whole lot more than a couple hundred pounds delta of stick weight.

which is why cats don't self right Fb is way out at the ama which is very far away from the axis of rotation. A skinny boat may flip over easier, but it'll also come back easier.


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## kevlarpirate

Paul

My statement was in reference to normal upwind sailing, I should have qualified that for you . We are talking a couple different subjects here, so you have to understand which statements belong with which topics. OK?
That statement is addresses kinetic energy and relates to Newton's first law
of......... yes, physics! 

Paulo. 
Very well written and believable article on these cats. 

He mentions getting broadside to waves while tacking ??? does he mean jibing through 270? Not trying to be funny here but perhaps tacking in catamaran talk means jibing in monohull talk. He didn't mention how much motoring he did, but I would guess he would need to motor if he were to do a real tack.

He also mentions it would take a lot more than 15 foot wave to capsize
yet he was quite nervous when broadside? I would like to know the angle the face of the wave was broadside to. In a well designed monohull
of course this would not be a big worry because you know you have plenty of reserve heeling before you get in the danger zone , but I question his statement 
because he actually did not know in his case how much reserve heeling he had left in the bank. 

He obviously had plenty of miles at sea to make highly qualified statements.
And I hope he was paid well, After reading his very well described encounter with the big ocean, I would think we could easily conclude
these big cats would do much better onboard a ship when delivery to a distant port is required. 

Personally, after reading his article, you could not pay me enough to take one of these things out of sight of land.


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## Paul_L

kevlarpirate said:


> Paul
> 
> My statement was in reference to normal upwind sailing, I should have qualified that for you . We are talking a couple different subjects here, so you have to understand which statements belong with which topics. OK?
> That statement is addresses kinetic energy and relates to Newton's first law
> of......... yes, physics!
> ...


The original topic is comfort on a sailboat, in particular the motion comfort index. You have come out strong in saying that it can all be answered with just the physics and you can explain why someone else's opinion is misguided based on the physics. Then to show how the physics is right you take it to the extreme. The point of vanishing stability, a cat in a survival storm, a mono doing a 360, racing to the windward mark.... In all these cases (except the last) the level of comfort is zero to negative when dealing with a cruising sized boat. The perception of comfort is very individual and not consistant. Trying to say that breaking this all down to the basic physics and you will end up with the explanation for the subjective feeling of comfort is not realistic. Small boats in rough conditions are uncomfortable.

Paul L


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## PCP

kevlarpirate said:


> .....He also mentions it would take a lot more than 15 foot wave to capsize
> yet he was quite nervous when broadside? I would like to know the angle the face of the wave was broadside to. In a well designed monohull
> of course this would not be a big worry because you know you have plenty of reserve heeling before you get in the danger zone , but I question his statement
> because he actually did not know in his case how much reserve heeling he had left in the bank.
> 
> He obviously had plenty of miles at sea to make highly qualified statements.
> And I hope he was paid well, After reading his very well described encounter with the big ocean, I would think we could easily conclude
> these big cats would do much better onboard a ship when delivery to a distant port is required.
> 
> Personally, after reading his article, you could not pay me enough to take one of these things out of sight of land.


I have no time to reply to your previous post about heeling angles and waves, but motion on waves is not the same on cats and monohulls. Monohulls heel a lot in a wave because the keel prevents them to slide laterally. When I have time I will quote from that article on the subject.

Anyway you can believe those guys (Wolfson unit) when they say that a cat is very difficult to capsize in heavy seas and breaking waves, much more difficult than a monohull. They are the most knowleadgeable guys in what regards capsizing. Of course, you may want to know why, but for that it is better to read that study.

About the Cats that guy was delivering, they are the less expensive and less seaworthy type of cats, the ones that are best suited for coastal sailing. If you want a comparison with monohulls, comparable, for example, with a 42 ft Jeanneau deck saloon. I believe that you would not want to be on a force 10 storm on one of those either. Yes, they can make it, like the cat, but they are not the better boat to do it.

Regards

Paulo


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## cormeum

Paul_L said:


> Small boats in rough conditions are uncomfortable.
> 
> Paul L


Some more so than others. I haven't been following kevlarpirate's arguments much but what I'd look for rather than some "index" is a hull form and weight (inertia) distribution that gives low accelerations in response to disturbing forces and has high lateral damping.

That's the physics of this in a nutshell.

The tradeoff being that such a boat will have a smaller righting moment at small angles of heel and will therefore tend to heel more- but that's life.


----------



## kevlarpirate

Very interesting read on the carbon masts. Thanks Viking

The very good points he makes are that it improves the ability to carry sail. That is fun. 

However, short of doing a FEA, it could result in substantially higher dynamic and impulsive loads on the rigging , chain plates mast step, mast compression and hull. The static solution to the problem by removing mast weight, cannot be 
assumed to be equal to the new dynamic forces of higher sail loading. It may be nothing to worry about in the end. 

My rigging buddies in Florida tell me rigging failures are not mostly from high winds with deep reefs ,and no.3’s, they are more common using heavy no.1’s, under 20 kts.

Other good points are aluminum masts can develop stress cracks as he mentioned. I have seen this on a couple of production boats which, to save assembly time, employ trick designs, for instance spreaders being held by one big pin drilled through a casting 
The casting being very solid produces a stress riser on the thin walled aluminum tubing and guess what …. Cracks. My 30 year old triple crane Sparcraft (both boats) have none of these problems. Personally I would dread ever losing them.
Because I may end up with something I don’t trust. 

Another very important point is the paint issue. 6ooo series aluminum is alloyed with copper and is prone to that white bubbling which is very unsightly and it happens to all masts, even the ones well primered with zinc chromate. Sooner or later it happens, and the cost of repainting is very painful as he states. Another reason I am very protective of my masts. And regularly check my rigging. They are anodized and after 30+ years, I have no issues, 

The author also states exactly the point I have been making re: moment of inertia.
He states twice the jerky movements. One statement he says he was seasick. 
This is exactly the price you pay for the fun factor. It is the comfort factor. 
Jerky movements are high accelerations, nothing else. 

When I mentioned cutting a wave in half and looking back at the hole we just made 
That is my fun factor, I would rather do that than realize another 2/10 of a knot
because I can take my number one up another 4 knots true. But if the extra 2/10 rings your bell, then great , it’s your boat. 

When I cut a wave in two , I don’t want to feel the boat pitch up. I want to blast through it. To me it’s kind of like the feeling I would get driving a monster truck over a car and crushing it. Now perhaps some of you are more sophisticated than me, but I like crushing things. 

A note I can make about carbon masts is they are not as torsionally stiff as an aluminum mast, so if you have swept back spreaders, you have some considerations to deal with as for standing rigging.

One issue I would disagree with the author is with lightning strikes. 

I had my 41 in Florida for 8 years and was blessed by not getting hit, however I have 
been close, so I will tell one account here . I had my boat in the yard and got a call that a boat next to me was hit. I raced down to the yard on two wheels around every corner ran to the boat to see the damage. First I can say, I made a couple of grounding spikes and had them pounded in the ground and cables up to the headstay and backstay , so I hoped they worked if I got any of the strike. My shrouds are connected to the keel by ¼ inch copper tubing conductors, so I was not worried about that, also I have one of those fuzzy things on the mast head. 

The boat next to me did get hit and on all six jack stands where the pads met the hull
The hull was pierced from the current. The jack stands had all been moved off to the side. Each area was black with soot where the resin was carbonized and missing.
You could take a pencil and push the glass fibers around and push the pencil right through to the inside of the hull. Some holes were worse than others.

The energy of an average strike is in the order of 200 kilojoules, about the energy of a hand grenade. That energy has to be dissipated somewhere. The current also shot 
Out the transom somehow and ended up in the boat behind the struck boat , so obviously there was plenty of energy there to do damage.

My point is this: all resins carbonize around 450 deg. F. so one would expect serious damage. Especially along any path where current must run on its way to ground.
This could be between the mast head and the upper shrouds. The resin is a essential stabilizer for the fiber. I don’t know how well the carbon conducts in such an event,
However, I would need much more data to convince me they are safe for a strike.
I would talk to insurance claims people first. 

Paul , My statements referencing physics and boat behavior are all consistent back to my first post. If you don’t find any thing of value, then just don’t read my posts and let others judge for themselves.

One note I will make is that I attempted to make a definition of what comfort was 
and was not . I proposed acceleration was the most likely agreeable definition.
No one came forward with any other definition. Including you.

The best that could be proposed was that it is different things to different people which gets us no where.

What is obvious is that comfort and motion produced by light weight boats are opposite. You can’t have have comfort on a sport boat or a ULB, in a developed sea unless your definition of comfort includes black and blue marks .

Paulo, did you read the insurance claim article? Humerous too. I don’t doubt 
There are better cats than others for passage making, but again when a 76 foot cat
Capsizes in 8-10 foot seas, that scares me , I would guess it was as simple as burying the lee hull , I have done that plenty on the Hobie, and I don’t see any reason you can’t scale that problem up. Gone for the weekend here . cheers, kev


----------



## PCP

cormeum said:


> Some more so than others. I haven't been following kevlarpirate's arguments much but what I'd look for rather than some "index" is a hull form and weight (inertia) distribution that gives low accelerations in response to disturbing forces and has high lateral damping.
> 
> That's the physics of this in a nutshell.
> 
> The tradeoff being that such a boat will have a smaller righting moment at small angles of heel and will therefore tend to heel more- but that's life.


Yes, heel more and more...till it capsize. Boats with smaller righting moments, will have a low positive stability curve and the energy needed to capsize them will be small. You can have a soft boat with a slow motion but that boat will be heeled a lot by each wave. That's not my idea of a comfortable motion and it is also dangerous.

A boat with a small righting moment at small angles of heel will not be capable of carrying any significant amount of sail and will be a slow and bad sailboat.

Things are not that simple .

Regards

Paulo


----------



## cormeum

PCP said:


> Yes, heel more and more...till it capsize. Boats with smaller righting moments, will have a low positive stability curve and the energy needed to capsize them will be small. You can have a soft boat with a slow motion but that boat will be heeled a lot by each wave. That's not my idea of a comfortable motion and it is also dangerous.
> 
> A boat with a small righting moment at small angles of heel will not be capable of carrying any significant amount of sail and will be a slow and bad sailboat.
> 
> Things are not that simple .
> 
> Regards
> 
> Paulo


Think of a flattened sine curve with the peak at 90 degrees. You don't need a lot of righting force at small angles of heel as long as it builds up when the heel angle increases. It'll be initially tender but will stiffen up fine at larger heel angles. (been there done that)
The added benefit is there'll be no (or a very small) area of inverted stability .
The example you show of a soft boat being repeatedy heeled by each wave had less to do with the righting moment than the wind pressure on the sails (which dominates) or the moment of inertia on that roll axis.
You're right, it's not as simple as it seems, is it.


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## Jeff_H

_quote kevlarpirate- Jeff you say:_

_"you would see that even if the boat with the weight added to its mast and the boat with weight added to its keel had equal roll moments of intertia, the boat with the weight up its mast would have a quicker roll rate, through a wider angle and with harsher de-accelerations than than the boat with the weight on its keel. "_

_This statement is false, it violates moment of inertia. _
_Total moment is the sum of the individual moments. Total moment _
_is independent of positions of individual moments. (first year physics)_

Kev: You are taking that quote out of context, but also as I see it, the problem with your responce is that you are over-simplifying and ignoring some of the component forces that impact roll rate and roll angle. I suggest that your re-read my post 89 where I explain how this works and perhaps you will understand in more detail the physics behind this quote and why it does not violate moment of inertia. I also suggest that you try to get your hand on a copy of Marchaj's Seaworthiness, The Forgotten Factor and look at the section where he explains all components of physics behind this in more detail than I go into here.

But to summarize, if both boats in my example (one with a smaller weight up its mast vs one with a heavier weight in its keel) had equal roll inducing forces, equal roll moments of inertia and equal roll resisting forces then you are correct that they would have equal roll rates and roll angles.

But where your comment misses the point is that these boats do not have equal roll inducing forces. In the case of the boat with the weight up its mast, as the boat rolls past vertical, that weight adds a roll inducing force. While in the case of the boat with the weight in its keel once the boat gets past vertical, that weight in its keel becomes a roll resisting force. The net differnces in the forces means that the boat with the weight up its mast has a greater overturning force and so would have a faster roll rate. And because it has a greater roll rate, that boat will also have a greater momentum. If both boats have identical hull forms and rigs, they will have equal dampening, and so the boat with the greater momentum will roll through a greater roll angle as well. Lastly because of this greater roll angle, the boat will also be further out of phase with the wave and so experience a greater impact/ deceleration. (First year physic regarding yacht dynamics in waves) - Jeff

_Kev quotes Jeff as saying: "If a boat has reduced roll and pitch angles can be reduced, its roll rates slowed, and if it can be designed with softer transitions,"_

_Kev says Jeff has it backwards: the only way to reduce pitch and roll angles is to lower moment of inertia and mass which will increase accelerations. _

Kev: Again, I suggest that you are taking my quote out of context and over-simplifying and also ignoring some of the component forces in your response. Roll moment of inertia and mass are certainly important, but these are not the only factors at play in determining roll and pitch angles and rates or impacting acceleration and deceleration. Just for example two cases which alter pitch and roll independent of moment of inertia and mass would be, 1) dampening, which will slow roll/pitch rates and thereby reduce momentum and thereby reduce pitch and roll angles. And 2) in roll motion, hull forms that progressively shift the center of buoyancy rather than suddenly shifting the center of buoyancy will reduce the severity acceleration and deacelleration by attenuating the distance/time over which the speed is lost. while increasing the amount of roll angle. 

Respectfully,
Jeff


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## PCP

cormeum said:


> Think of a flattened sine curve with the peak at 90 degrees. You don't need a lot of righting force at small angles of heel as long as it builds up when the heel angle increases. It'll be initially tender but will stiffen up fine at larger heel angles. (been there done that)
> The added benefit is there'll be no (or a very small) area of inverted stability .
> 
> *The example you show of a soft boat being repeatedy heeled by each wave had less to do with the righting moment than the wind pressure on the sails (which dominates)* or the moment of inertia on that roll axis.
> You're right, it's not as simple as it seems, is it.


The sail the boat can carry is directly related with the boat's righting moment at small heel angles (till 35º). There is no doubt about this.

If you have a low righting moment at small angles heel, you can only carry a very limited sail area, and you need sail area to sail a sailboat. So your tender boat, that needs sail area to sail, but that has not the riggting moment (at small angles of heel) needed to contra balance the wind force on the sails, will heel slowly but a lot.

If the righting moment curve has small righting moments on small heel angles, it will be a flattened sine curve (as you say), but will not peak at 90º of heel (they never do) but at around 65/70 degree. That's a typical curve of an old designed boat, for instance a long keeler from the 60's.

If the curve has big righting moments on small heel angles, you will have a very vertical curve that peaks high at 50/55 degrees of heel and then comes down in a more vertical way. That's a curve of a fast modern boat.

The area under the positive part of the curve (representing the energy needed to capsize the boat) will be much bigger on the more vertical sinusoidal curve than in the flattened sinusoidal curve. The max righting arm (GZ) of the first curve will be almost the double of the one from the second one. The curves will have typically very different AVS (or LPS) points. The first one will have an AVS between 115 and 135 degrees and the last one, an AVS between 135 and 180 degrees. But, at 90º of heel the bigger curve will have normally a bigger righting moment, compared with the more flattened curve.

Considering boats with a similar mass, the boat with the flattened sinusoidal curve will be a tender boat, much more easily capsized (and also with a better rerighting ability) while the boat with the more vertical curve will be a much more stiff boat, a much harder boat to capsize, but also a boat that will need more time to reright. And, of course, the last will be able to carry probably more than the double of the sail, comparing with the old boat, making it a much better sailing boat.

Please, believe me on this, it is really like that .

That's why the boat designers went on the direction they did on the last 50 years, that's why modern boats are what they are. The objective is to design faster, safer and better sailing boats.

That does not mean that old designed boats didn't have some advantages, but all boats are compromises and what Designers do is try to get the best compromise to each boat's use, from racing to cruising, but never forgetting that the first objective of a sailboat is to sail and to sail well and probably the second objective is to design a boat that sailors can afford.

Regards

Paulo


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## cormeum

Paulo, I think we're talking about the same thing in two different ways- Skinny boats having a max righting force between 75 and 90 degrees as we both said will heel easier but as you agree, will also re-right easier. I don't necessarily agree that sailing at heeling angles of 15 degrees is any magic number, the Universal Rule or older RORC rule boats that regularly sailed at twice that angle still cooked along- maybe not quite as fast as a stiffer boat but certainly adequate for cruising speeds. As I said the tradeoff is an easier motion. FWIW, a number of the Universal rule boats had righting moment maxima at right around 90 degrees and AVS's around 180. And yes, they did their sailing on their ears. You also have to realize that the rigs of those days had a lower center of effort than modern rigs which ameliorated the heeling to some extent.

I think we have to agree that the real mover regarding designs has been to win according to the then prevalent rule not necessarily "Better, faster or safer boats". With some notable exceptions.


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## PCP

cormeum said:


> ...I think we have to agree that the real mover regarding designs has been to win according to the then prevalent rule not necessarily "Better, faster or safer boats". With some notable exceptions.


Well, I have to agree that like in the auto industry, racing have been the real engine of sailboat design development. You don't win ocean races, Transats or circumnavigation races without better faster and safe boats. Particularly In the last 20 years, great advances have been made having as base the developments needed to allow safe solo ocean sail racing.

These advancements have been successfully integrated on cruising boats, made them safer and more easy to use. And I am not only talking about hull and keel design but also about stronger materials and building processes, furlers, geenaker light furlers, better autopilots, and lots of other things.

Jeff has pointed out the importance of IRC on the development of better boats and I think that today the bigger contribute to cruising sailboats design come from Open boats.

Anyway I don't want to give you the impression that I don't like skinny boats (as you call them). There are some few modern ones around, light hi tech fast boats that I consider very beautiful and interesting. Their stability curves are not exactly like the ones from the old heavy and slow skinny boats, but they have also an easy motion.

I like them so much that some years ago I went to Denmark to test sail one and I can tell you, they are fast....and they heel a lot.

They have advantages and disadvantages over other types of modern boats, I would say more disadvantages, being the most obvious the price. The real problem is that a "skinny" 40ft has the interior space and overall stability of a 36/37ft "normal" modern boat&#8230;.and costs the same as a 40ft "normal" boat.

I think that is the real reason why they are so marginal on the market.

But as I say, I like them, they are just beautiful.

Regards

Paulo


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## seabreeze_97

Jeff, additional weight up the mast does not act to increase the roll speed. Yes, it will possibly net a slightly greater roll but only in as much as it will take the righting effect of the keel to reverse....and that starts as soon as the boat begins to roll. Lemme say that again. As soon as a wave or blast of wind hits the boat, it begins to roll. Both boats' keels immediately begin to counter this, thus slowing the roll, not allowing acceleration because of heavier mast weight. The heavier masted boat will react slower as there is greater mass and leverage to act against the outside force initially. Depending on the magnitude of the forces at work, the heavier-masted boat may actually not roll as much in totality as a shorter or lighter-masted boat since it will initially respond more slowly, and with more resistance to the outside force. At worst, a heavier masted boat will be slightly slower to reverse a roll with a given amount of ballast. Again, slower motion, greater comfort...less jerkiness. Will it roll further? Again, maybe. It will begin the roll more slowly, so the total roll will still be very close to the lighter masted boat. The keel has more time to act to right the boat as it is initially responding more slowly. It has been shown that mast weight is essential to resisting capsize (post-FastNet). The solution is not to use ultralight masts and greater ballast weight. This will only make the boat even more likely to capsize in big seas. If the mast is such a liability, why do ballasted boats become so unstable? No reply necessary, it's a rhetorical question. Since the keel is going to be less than say 8ft down, where the lever of a 40ft+ mast (give or take) is much higher, this would result in much less added weight to resist roll. What's the old adage? 50 lbs aloft requires how much ballast to counter? All else being equal, wouldn't the boat that is 1000lbs (or 2Klbs for that matter) be lighter and faster, at least in lighter conditions? Heavier mast, or even a taller lighter mast dampens motion better, weighs less so acceleration is better, maneuverability is better, and it's more comfortable. Further, taken to the ultimate example, your model would appear to have a super heavy keel bulb 10ft down, hi-tech structure and rig, very light weight. Again, great in calm, specific (racing) conditions, but it'd suck in the real world.


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## PCP

Kev has posted a link to what is called "Technical papers" by John Holtrop.

On these papers Holtrop says, about dynamic stability and wave encounter:

*"Dynamic Stability controls how much the boat rolls in response to a transient wind gust or violent wave. ...Heavy displacement helps dynamic stability, but the center of gravity is not much of a player .. The most important factor in dynamic stability, however, is the boat's roll moment of inertia. "*

Technical Articles

It seems that for him (as for Kev), the most important factor in preventing capsizing, or in boat stability is inertia and particularly roll moment of inertia.

If this was true, then all the work of the naval architects and naval engineers that have defined the parameters that should be considered to access boat stability and capsizing risk, for the European Community recreational craft directive (that classify the boats accordingly to their stability in several categories, for different uses), would be completely biased and would serve no purpose. They don't have considered that moment of inertia (that is one of the factors) was the dominant factor in boat stability.

Also, on all papers that I have seen about capsizing and boat stability, that factor is not considered the dominant one, among the several that are normally considered: Static stability; Roll mass moment of inertia; Surface area; Roll damping; Speed.

Someone is wrong, or John Holtrop, or many of the best European and American Naval architects and Engineers, including the ones from the Westlawn school of yacht design and the ones from the Dept. of Naval architecture of the US Naval academy. Nobody considers the Roll moment of inertia as the dominant factor on stability or in capsizing a boat. Never saw anybody saying that, except kev and Holtrop.

Let's look at Holtrop's experience in Naval Architecture:

"&#8230; My engineering background is rock solid, my artistic ability is what it is&#8230;. I have built boats using wood strips, stitch and glue techniques, and molded fiberglass. Some have been better than others, but they all floated without breaking!

&#8230;My boating experience, which started 50 years ago with the construction of a modified canvas covered canoe. .. Growing up is southern California let me spend a lot of time "messing around with boats", so I jumped at the chance to apply for admission to the California Maritime Academy. .. Not much theory, but a lot of "hands on" experience. I specialized in Marine Engineering. The highlight of my time at the academy was the design and construction of a model steam engine. After graduation, &#8230; I worked in the Merchant Marine for five years, mostly hauling war material to Viet Nam. &#8230;went back to school and eventually graduated with a degree in mechanical engineering.

&#8230;.So why buy plans from some guy on the web that no one ever heard of?

Let´s see what some of the best researchers on waves and capsize with conclusions based on test studies say about Inertia and Roll Moment of Inertia:

*"These studies showed that in beam seas the location of the vessel relative to the breaking position of the wave is critical. If the vessel is caught in the curl of a plunging breaker&#8230;capsize is possible in waves as small as 1.2 times the beam of the vessel.

The roll moment of inertia is also an important parameter because a vessel with a large value of this parameter will roll to a smaller angle on impact, but expose the deckhouse &#8230;to the full impact of the plunging wave jet."*

In " Capsize resistance and survivality when small vessels encounter extreme waves" by Bruce Johnson, from the US Naval Academy.

Naval Architecture and Ocean Engineering Department at the U.S. Naval Academy

Comparing two similar models with different centers of gravity:

* "In the smaller (breaking) waves, the high variant (VCG) was knocked down to a lesser angle than the low VCG variant." *(On bigger waves both versions were rolled).

Comparing two similar models with diferent inertia:

*"About Inertia variation (all things equal, different inertia on models): "The inertia of the fin keel parent model (nº1) was reduced by 40% of the original. Tests in cross wave conditions indicated no discernable change in response to the wave. In the downwave conditions the high inertia variant pitch poled on more occasions than the low inertia version."*

"An investigation into the stability of sailing Yachts in large breaking waves", by A. Claughton and P. Handley from the Dept. of ship science, Southampton University

It seems to me that Kev is giving too much credit to roll moment of inertia, to say the least.

Regards

Paulo


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## Jeff_H

seabreeze_97 said:


> Jeff, additional weight up the mast does not act to increase the roll speed. Yes, it will possibly net a slightly greater roll but only in as much as it will take the righting effect of the keel to reverse....and that starts as soon as the boat begins to roll. Lemme say that again. .


I don't care how many times you say it; you would still be mistaken, at least given the example in my earlier post 89. I know that intuitively you disagree with this, so I suggest that you read Marchaj's description of the components forces of roll (roughly page 215 of the edition of "Seaworthiness, the Forgotten Factor" that I referred to).

<OI chose some pretty big numbers for my example in the hopes of making the example more intuitive, but apparently that did not work. So I will try to look at some numbers that are closer to real life. 

<OA few years ago an acquaintance had a 36 foot boat that needed a new mast. He had gotten two proposals from the same spar shop, the less expensive one was for a straight spar with a stock masthead fitting and stock stainless steel spreader fittings and the slightly more expensive one was a tapered spar with a welded masthead fitting and spreader fittings, all of which matched what came on the boat. The mast maker had calculated the additional weight of the stock masthead and the non-tapered spar at roughly 8 lbs, and I had calculated that the centroid of that weight was roughly 35 feet above the waterline. The spreader bases were roughly 5 lbs heavier and 20 feet above the waterline. And he was adding radar which added roughly 35 lbs (with the SS support bracket and guard) roughly 20 feet above the waterline. We compared that to pole-mounted radar, which added something like 65 lbs with its centroid roughly 9 feet above the waterline.

<OCumulatively, this would add quite a bit to the moment of inertia of the boat with the stock spar and parts, mast mounted radar as compared to the boat with the tapered welded spar and with pole mounted radar <O</O
In rough terms, the additional roll moment of inertia (assuming that the roll axis is at the waterline as it often was on boats from the 1970's at low heel angles and assuming Ir=mass x L squared) the increase would be as follows: 
<O</O
Non- tapered spar 8 x 35 x 35 = 9,800 Lb.Ft. sq'd<O</O
Spreader bases 5 x 20 x 20= 2,000 Lb.Ft. sq'd<O</O
Radar (35 x 20 x 20) - (65 x 9 x 9) = 8,735 Lb.Ft. sq'd<O</O
For a total increase in the roll moment of inertia of 25,800 Lb.Ft. sq'd<O</O
<O</O

If we want to duplicate the same increase in the moment of inertia by adding a bulb to the bottom of the keel with the tapered spar, it would require a 716 lb bulb with its centroid roughly 6 feet below the roll center. 

<O</O716.5 x 6 x 6= 25,800. 

<OBut of course at this point we need to take this additional weight out of the boat if these boats are going to remain equal in other regards. Here I will propose some places to cut the weight. I'll start with a pet peeve of mine, liners. For some reason, boat builders seem to feel the need to install fiberglass liners on every inch of the hull. Since, for environmental reasons, most hulls and decks are vacuumed bagged in one form or another these days, it would be reasonably practical to eliminate the liner and paint the interior of the hull. By the same token, the combination of more complete interior framing and vacuum-bagging which is the norm today, results in lighter hull and deck than a lower-tech hand-lay-up of years yore. <O</O
<O
I calculated the net weight savings of eliminating the hull and deck liners (but retaining the internal molded frames) and reducing the hull weight/framing by 6% would be approximately 525 lbs of the 716.5 lbs of weight that we are trying to save. <O</O
<O</O

And if we change from the varnished 5/8" teak faced plywood that was so prevalent a few years ago to painted 10mm okome plywood that is getting popular for interior flats and non-major structural bulkheads, by rough calculation we should be able to save not only construction cost, but by a rough calculation a little over 200 lbs in construction weight getting us down to a rough weight parity with the boat with the heavier rigging weight. <O</O
<O</O

At this point, we have two boats with equal moments of inertia at small heel angles. (I would suggest that we ignore that the roll moment of inertia will decrease on the mast weighted boat and increase on the keel weighted boat at big heel angles as the roll axis moves upward as the center of buoyancy moves up the topsides).

And if these boats start out vertical, and they both are hit by the same wave and they both have the same roll moment of inertia they would both initially roll at the same rate. 

But as they start to heel, the horizontal offset between the weight up the mast and the center of buoyancy will shift in the direction of the roll and add to the force of the roll (see Marchaj). At the same time, the horizontal offset between the weight in the keel and the center of buoyancy will shift in the direction opposite to the roll and subtracting from the force of the roll, slowing the weight of the roll. At 90 degrees of heel, the mast weight adds 500 ft. Lbs. to the roll moment, and the bulb would reduce the roll moment by 4,300 ft. Lbs. for a net difference in roll moment of 4,800 ft. lbs. It is that difference in roll moment that results in the boat with the weight up the mast having a faster roll rate and rolling through a wider roll angle, dispite having an equal roll moment of interia. 

I know you are having trouble visualing this. I will use Kev's example of a wheel to try to explain this. If you visualize a vertically mounted wheel with a large weight bolted to it, that is turned by a small motor barely able to turn the wheel, at all times that wheel would have the same rotational moment of intertia. 

But if you visualize the section of the revolution where weight is on the side of the wheel that the motor has to lift that weight vertically from the bottom to the top of the wheel, the motor will have to overcome the force of gravity acting on that weight and the wheel will slow down. But once the weight gets past the top of the wheel, the rotation of the wheel will be assisted by the force of gravity acting on the weight, and so the wheel will turn faster on the way down. 

The same thing occurs when you add a weight high in the boat in an effort to slow roll and reduce the likelihood of capsize. While the added roll moment of inertia will initially slow the roll rate of the boat, through out a roll cycle it will increase roll angle and speed, at least relative to trying to increase the roll moment of inertia by adding weight low in the boat as is the common practice on modern designs today. 

Respectfully,
Jeff


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## kevlarpirate

Paulo ,

Your conclusions about me are totally off base. 
It has now become apparent to me that you do not know how to interpret the static curves, I am concluding you have it totally backwards. 

re: post #28, to allow me to understand your thinking , could you evaluate the differences between the Hanse 430 and the 36 foot Bavaria? just those two. OK?

Jeff , this post 98 you keep mentioning, not yours
Also, as i have mentioned , you are talking to an engineer, Please don't attempt to humor me. I don't humor. 

I have read all your posts and I can conclude not only are you totally new to the concept of moment of inertia , in addition, you are cherry picking date to support a pre disposed preference. Won't work , but I am happy you are now down with the concept of radius( length) squared. 


Palo , I read that report years ago. This test was to see differences between hull shapes and a couple of variables , no boats had masts. The inertia they mention was not specified or defined and absolutely cannot be concluded to represent the effect of a mast as part of the total system in any way what so ever. 

The other conclusions they were able to make is exactly what I have known for some many years, not specific to this conversation, but still related.
Skinny boats win, fat light weight ones lose. 

As for Holtrop and Johnsons comments, they hold true and I agree with them. 

I personally don't care what you believe of mine and what you don't. 
I am however interested if you have the static thing backwards , so please answer, but if you don't I will consider my conclusion correct.

And again, any reader doing technical due diligence will be able to 
sort all this out.

BTW my boat slices waves, like swatting flies. No lightweight boat of the same length will ever be able to do that.

Engineers have a certain language and writing , just like lawyers have their language and style. I don't pretend to be a lawyer , I don't think either yourself of Jeff should try to be engineers.

You are both highly impassioned romantic types and you have a particular boat style
you are very fond of. I don't believe for a second, that boat "style"
is either comfortable or safe or had good manners in a well developed sea, storm or even at anchor. Big broad transoms slam all night long
and all the boats you are fond of pound going up wind even in the smallest of chop.

I have sailed the types of boats you are fond of, and i have been on board them on the mooring cans .. To call a cruising version of these boats you describe is laughable. they can't even survive a kiss from a whale .
they sink!

kev


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## Jeff_H

Kev,

You are right about post 98 being someone else's post. I'm sorry, I mistyped. The post that I was referring to was post 89. (For the clarity of someone else reading this thread, I went back and changed that mistype in earlier posts.)

Just for the record;

I have always used the Radius of gyration squared when calculating rotational moments of inertia.
On a number of occasions and forums you have accused me of selecting data to support my bias. I suggest that it might be helpful to the conversation, to someone reading this discussion, and to my own knowledge if you actually pointed out one or more of those cases.
You have suggested that I am new to the physics of motion at sea, and compared to some I certainly am since I only started looking into motion at sea back in the 1960's.
At the time my yacht design teacher worked for S&S. S&S was evaluating Titanium for the 12 meter Intrepid's upper mast with the goal of reducing its weight. I had assumed this was to increase stability and therefore reduce heel angle, but he explained that S&S was far more concerned with pitch and roll, but mostly pitch. That lead to a discussion of the bow shaping on Intrepid, which was modeled in part with the intension of progressive dampening of hobby-horsing, which had been a problem on earlier 12 meters. It was the first time that I began to look into motion at sea. It has been an strong area of interest of mine ever since.​

You refer to the boat that I own ( I don't know what kind of boat Paulo owns) saying things like, _"I don't believe for a second, that boat "style" is either comfortable or safe or had good manners in a well developed sea, storm or even at anchor. Big broad transoms slam all night long __and all the boats you are fond of pound going up wind even in the smallest of chop."_
All I can say is that you obviously have never sailed on the model boat that I own. Having over a dozen owned boats as varied as a 1939 Stadel Cutter, 1949 Folkboat, half a dozen CCA era boats, a few IOR era boats, and several MORC boats. I once sat down and listed the boats that I had sailed on and came up with having cruised, raced and day sailed on close to 100 different designs over the years, that varied from traditional gaff riggers to modern sportboats.​
I came to purchase the type of boat that I own, not out of some pre-conception, but out of a long evaluation of various boats that I have sailed. I understand that there are some shortcomings to all boats, and mine is no exception, but I would say that you got it very wrong when you talk about her motion in a developed seaway, chop or at anchor. My boat was single-handed into the US from South Africa and prior to purchasing my boaty I discussed the behavior of these boats with a diverse group which included Dudley Dix, a couple who sailed one up the Atlantic from South Africa to Scotland, and a fellow who had single handed on from South Africa to the Carribean the first 8 days of which were in winds that did not drop below 30 knots and hit gusts well into the 50 knot range and seas he decribed as being above the mast. All described these boats as having great offshore behavior.

In terms of sailing in short seas, I would say that one of things that I like about my current boat is its ability to slice through waves when sailing going upwind in a chop; rather than pounding, especially relative to the boats that I have owned and sailed on over the year. As any knowledgeable designer will tell you, pounding is more a more matter bow shape than displacment.​
And while my boat, kites more on the anchor than I would like, her stern does not slap, at least not as badly as the long over hang CCA era boats that I used to own.​
But more to the point, my boat is a 30 year old design. While a pretty advanced design for its day, it represents a snapshot in time of a time long ago. Based on my experience on board the better newer designs, they have far eclipsed the design thinking of that era in producing seaworthy and motion comfortable boats.​

I respectfully suggest that you need to spend more time sailing on some of the newer designs before jumping to mistaken opinions about their behavior. Over and over again you keep referring to ULDB's of a design era that is nearly 40 years ago. The newer designs are not ULDB's. In fact they do not weigh all that much less than similar length on deck boats from 30 years ago, but a huge amount has changed in hull modeling and weight distribution since that time which have greatly improved the motion comfort and seaworthiness of these designs. And so, I suggest that if you spent more time sailing on some of the really newer designs would actually experience their motion comfort and sailing ability first hand. I think you would be pleasantly surprised.
Respectfully,
Jeff


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## cormeum

Now Boys,
How's this: go to Toys R' Us and get a toy sailboat (Bosun boats are pretty good) and fill a bath tub with water. next tape a weight to the mast and set it oscillating transversely. Time the oscillations. Next take the weight off and time it again. 

Nothing like a little experiment  

N.B. as the math has no scaling factors, the test will be valid.

You can post the results on You Tube.


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## blt2ski

cormeum,

I like that idea. BUT, i have to ask a question, this works IMHO when at rest at anchor. How does this wt effect one when sailing in an X knot breeze? and how does the breeze effect the rolling? While the wt at the top will help the roll stop quicker at anchor, will the wt at the top allow the boat to right itself with wind gust as quick? or allow it to capsize quicker? My gut says the wt at the top of the mast when sailing should not do as well as when not, but could see the at rest being better. 

Anyway, better add some kind of fan to the experiment, along with a BIG bath tub, or swimming pool so the fan can add wind equal to the experiment.

Marty


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## cormeum

blt2ski said:


> cormeum,
> 
> I like that idea. BUT, i have to ask a question, this works IMHO when at rest at anchor. How does this wt effect one when sailing in an X knot breeze? and how does the breeze effect the rolling? While the wt at the top will help the roll stop quicker at anchor, will the wt at the top allow the boat to right itself with wind gust as quick? or allow it to capsize quicker? My gut says the wt at the top of the mast when sailing should not do as well as when not, but could see the at rest being better.
> 
> Anyway, better add some kind of fan to the experiment, along with a BIG bath tub, or swimming pool so the fan can add wind equal to the experiment.
> 
> Marty


In think in this we're just testing roll period. For gusts, an impulse is an impulse whether it's your finger or a fan. A dynamic oscillation test can be done with fans in a pool (or get a kid to handle bellows in the tub)- Good idea for another video. We also could get the kid to do some waves- mom won't complain, it's for Science.


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## Jeff_H

Cormeum: 

I think that we are all in agreement that whether you add a weight at the top of a mast, or bottom of the keel, it will increase the roll moment of inertia, and that will slow the roll rate of the boat, which is all that your prioposed experiment will show. (As a teen, I actually did a similar experiment with a full sized boat and a plumb bob in a bucket of water for my outside experiment for a high school physics course.) I don't think any of us disagree with the impact of increasing roll moment of inertia. 

But I do not believe that is the issue that we are discussing. The discussion point that seems to have triggered this discussion is the usefulness of the Capsize Screen Formula or the Motion Comfort Index. Neither contain any data about weight and buoyancy distribution, or dampening, which are key elements in determining the likelhood of a capsize or the motion comfort of the boat, and which from the current scientific thinking that I have been following would suggest are better predictors than the limited number of variables contained in either of these equations. 

Jeff


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## kevlarpirate

Jeff, My beef is not your boat, I'm sure your boat is exciting enough for you to justify ownership.

The style of boat I refer to is the latest out there I don't want to be specific, These boats claim cruising ,versions. I call that a joke. More specifically disinformation,
meaning a deliberate attempt to mislead, taking advantage of the inexperienced
or highly emotionalized potential buyers. I have been saying the same thing all along.
I highly suspect these calculated static curves are manipulated. I called a MFG and he waffled when I pressed for details. 

I also have a beef with statements about having great advancements after IOR , I say hogwash. Static curves for one got worse
Truth be told, design changes were supported solely by the power of the fact "speed sells" mostly downwind. Reducing weight was key

I have nothing against speed, but the sacrifices; comfort, noise, breakage, expense of repair are there and they are not going away. I consider this latest breed as throwaway boats. Buyer beware.

Boats are sold through testosterone, and if necessary, can I at least convince the wife she will be comfortable...Having both worlds is impossible , you can't make whiskey out of wine. 

These boats sail on their leeward chine with the crew gathered on the aft rail 6 feet above the water , with the windward underbody out of water and 6 inches of the rudder exposed, and the bow almost buried. A 2 foot chop , the foredeck is soaking wet .... BTW I was/ am there, when I am not sailing on one of these , I am doing RC or on a chase boat , taking pictures for fun. BTW this in in 10KTS true, 
I am out there for almost every race. 

My friend has a latest design, water ballasted 35, he is an engineer, he knows exactly what he bought and why. I mentioned XXXX says they have a cruising version of their 40. I said it at the wrong time , he had a drink in his mouth which he almost lost .

It's a joke Jeff. We sail to Catalina and I go onboard many boats on moorings too. I If you believe I am old school , out of touch, you are mistaken. 

As a note, I sailed a 40 ft canted keel twin foil, what a joke, a monstrosity
of unnecessary complication. we were bounced around like a toy and never enjoyed anything.

My disagreement with you is your belief that the devil is in the details.. That somewhere in the subtle shaping of hulls here and there a perfect baby pops out.

I agree a baby pops out , but when it comes to both performance and comfort combined, you can't get around the mass thing. Mass (includes moment) wins, peak of the curve.
Buy a big massive powerful boat, as much as you can possibly afford and learn how to take care of it so you don't end up in the poor house. 

I mentioned (only once) a 50 foot ULDB going to weather pounding and the hull quivering
every wave I took , my chest hit the wheel. I had to stay an extra half a foot back.
I don't call that fun. At anchor, it was quite noisy and irritating, no improvement in my book. 

As for moment of inertia, the article on the carbon mast tells all. Owner states 
noticeably jerky upwind movements, You could tell he did not expect this, Personally I would never want that, If I did that to my own boat, I doubt if I could rationalize it considering the only speed gain would be revealed only by the knotmeter. The normal visual input would not reveal an extra 2/10 knot , however the accelerations would be felt.

Yes, I agree the titanium, bow section point you raised, but that was not about comfort
That was about a few hundredths of a knot upwind. 

I will end with incident acct. It was the Santa Barbara , King Harbor race a few years back . A 32? foot sport boat blew up In the Channel Island area in what we 
would call rugged sailing , gusting above 30 knots. Anyway, the boat launched a couple crew into the water. Big wide cockpits do this quite easily considering there is little to grab on to or lean into. One got back on the other didn't . The boat was dragged away 
on it's ear faster than the crew could swim. By the time the crew got the ASO down and the #3up they could not work back upwind. These were Transpac veterans, no dummies
Almost 3 hours later , the crew was retrieved by another boat. Once you drill down into how such an incident can take place, I think we can agree it is a chain of compromises
all pointing toward the boat no longer takes care of the crew. Designs are based on 
principally down wind speed, everything in it's path is marginalized. 

have to run, kev


----------



## cormeum

Jeff_H said:


> Cormeum:
> 
> But I do not believe that is the issue that we are discussing. The discussion point that seems to have triggered this discussion is the usefulness of the Capsize Screen Formula or the Motion Comfort Index. *Neither contain any data about weight and buoyancy distribution, or dampening,* which are key elements in determining the likelhood of a capsize or the motion comfort of the boat, and which from the current scientific thinking that I have been following would suggest are better predictors than the limited number of variables contained in either of these equations.
> 
> Jeff


They're pretty useless then. We agree on that. 

Taking a boat on a sea trial in crappy weather will give you better data than trying to solve a series of coupled differential equations-certainly better than looking at a screen that accounts for only minimal inputs.

No model quite like reality.


----------



## PCP

Jeff_H said:


> You refer to the boat that I own ... saying things like, "I don't believe for a second, that boat "style" is either comfortable or safe or had good manners in a well developed sea, storm or even at anchor. Big broad transoms slam all night long &#8230;and all the boats you are fond of pound going up wind even in the smallest of chop."
> 
> All I can say is that you obviously have never sailed on the model boat that I own. Having over a dozen owned boats as varied as a 1939 Stadel Cutter, 1949 Folkboat, half a dozen CCA era boats, a few IOR era boats, and several MORC boats. I once sat down and listed the boats that I had sailed on and came up with having cruised, raced and day sailed on close to 100 different designs over the years, that varied from traditional gaff riggers to modern sportboats.
> 
> I came to purchase the type of boat that I own, not out of some pre-conception, but out of a long evaluation of various boats that I have sailed. I understand that there are some shortcomings to all boats, and mine is no exception, but I would say that you got it very wrong when you talk about her motion in a developed seaway, chop or at anchor. My boat was single-handed into the US from South Africa and prior to purchasing my boaty I discussed the behavior of these boats with a diverse group which included Dudley Dix, a couple who sailed one up the Atlantic from South Africa to Scotland, and a fellow who had single handed on from South Africa to the Carribean the first 8 days of which were in winds that did not drop below 30 knots and hit gusts well into the 50 knot range and seas he decribed as being above the mast. All described these boats as having great offshore behavior.
> 
> In terms of sailing in short seas, I would say that one of things that I like about my current boat is its ability to slice through waves when sailing going upwind in a chop; rather than pounding, especially relative to the boats that I have owned and sailed on over the year.....
> 
> &#8230;..But more to the point, my boat is a 30 year old design. While a pretty advanced design for its day, it represents a snapshot in time of a time long ago. Based on my experience on board the better newer designs, they have far eclipsed the design thinking of that era in producing seaworthy and motion comfortable boats.
> 
> *As any knowledgeable designer will tell you, pounding is more a more matter bow shape than displacment*.
> 
> Jeff


 I have to say that you seem to have some experience, in what regards extensive "test sailing" different kind of boats

Regarding bows and pounding, of course, you are right. Let me show you the moment I started to consider very large transoms boats on a different basis, regarding sea motion and pounding. I believe it was in 2005, at the Paris boat show and I was looking at a 40class boat (I have taken some photos). I keep going to the front of the boat, looking at the bow shape and to its fine entries, and going to the back, and looking to the huge transom and keep thinking that it made sense: Huge stability downwind, limited pounding upwind.

Looking at the bow and at the transom, separately, hardly you would think that they belong to the same boat. 
















Of course, this is not a cruising boat, it is a racing boat, but in the last years this principle has been applied to modern cruising boats.

That has allowed cruising boats to be optimized for sailing at 17º/20º degrees of heel, boats that can plan and go faster and safely downwind ( faster 4 to 8K) and that have an acceptable, almost comparable motion upwind. They will point a little less than the typical cruiser/racer (less than 5º) but are faster at 40/45º, making the same way, in a less stressing and more comfortable sailing position (being at that position, probably more comfortable than a more traditional modern designed boat, hard at the wind).

My wife, that knows one or two things about boat comfort and motion (sailing with me for many thousand miles), after test sailing the small beam option, ( I like both kinds of boats, for different reasons : Small beam and big transom large beam) declared that she wanted the other option, a big transom beamy boat with fine entries. The main reason is the 10º difference in heeling sailing position.

Only the ones that didn't try to cook (or sleep) in a boat heeled 30º would not understand her choice.



Jeff_H said:


> And while my boat, kites more on the anchor than I would like, ..


Jeff, my previous boat had that problem, probably in a worst way than yours. With winds over 15k mine swung a lot at anchor. That was uncomfortable and on very strong winds that also put lateral stress on the anchor.

I have designed a stabilizing sail that has reduced that motion to a fraction, certainly less than half of what the boat used to do. On very strong wind it has the added advantage to take strain from the anchor (with strong winds, on each side of the small swing, the chain is not making almost any force because the boat "sails" a bit forward).

I have been approached by many cruisers that, being at the same anchorage and after seeing the results, have asked me permission to copy the model. It takes less than 5 minutes for just one person to rig it. 








Regards

Paulo


----------



## kevlarpirate

Jeff, in reading Paulo's reprint you state that I "obviously" have not sailed a boat similar to yours.
Please tell me which boats of these (35-40 ft range) are closest to yours I have also raced hot dogs mostly, offshore on a couple too

J35, Express 37, C&C 37R, Schock 40 TFCC, Farr 40, Santana 35, Creekmore 33 I think, J40 (too heavy) Farr 36 one ton 1980? , J-105

Having sailed and raced these, tell me if you think I am qualified to forward 
any findings of facts? 

Paulo, are you still working on the answer to the static curve question? (chuckle)


----------



## kevlarpirate

Paulo , forgot to mention, I said this before, but I sail my own boat 
at 15 to 17 degrees heel too. I can do it with whatever sail I choose to keep the boat at that heel. I get within 2/10 of my target speeds. 
Point being? yes , your manufacturer is actually telling you that is the ONLY range the boat is food for .... yes, another compromise. and I am sure the list goes on...

No one forces you to sail at 30 degrees heel. I agree if your boat is not easily driven , you may be forced toward that end of the envelope. But to actually have to do it is typically unnecessary and certainly not comfortable. 

You may ask however , how one of these boats you want so much would behave if you were forced to sail at 30 degrees. You may find them unmanageable. Something I don't have to be concerned with not having a wide transom. Did you say that could be handled with twin rudders? (chuckle)


----------



## Jeff_H

_


kevlarpirate said:



Jeff, in reading Paulo's reprint you state that I "obviously" have not sailed a boat similar to yours.

Click to expand...

_


kevlarpirate said:


> _Please tell me which boats of these (35-40 ft range) are closest to yours I have also raced hot dogs mostly, offshore on a couple too_
> 
> _J35, Express 37, C&C 37R, Schock 40 TFCC, Farr 40, Santana 35, Creekmore 33 I think, J40 (too heavy) Farr 36 one ton 1980? , J-105_
> 
> _Having sailed and raced these, tell me if you think I am qualified to forward _
> _any findings of facts? _
> _(chuckle)_




None of these are particularly similar to my boat. The J-35, and J-40 are derived from 1970's era MORC thinking adapted to larger boats. They have much flatter bottoms, with their center of buoyancy further forward fuller bows and the more pinched transoms that was typcial of boats of that era and genre. The J 105 is only slightly improved next generation thinking and optimized as one-design race boats.

The Santana 35, Creekmore 33, Farr 36 One Ton, and C&C 37R are all IOR derived designs with very different hull forms and comparatively miserable motions. The Farr 40 is probably closest, but these were built as full blown, grand prix level, one-design race boats with their designs evolved from IMS thinking of their day. In terms of speed, as well as overall hull and rig design, they are very advanced designs compared to my boat, but my boat was designed primarily as a performance cruising boat, they were solely designed to be raced.

Probably the closest of the designs on your list is the Express 37. This is one of my favorite boats from that era, and one which is faster than my own boat on almost all points of sail. But I did not choose to buy an Express 37 partially because it was more optimized for reaching and running, and racing. They also have less tankage. With regards to this dialogue, as much as I liked the Express 37, I was concerned that the Express 37's fuller bow sections gave it a less comfortable motion in a short chop (especially beating) than the boat I chose to buy, which has a very different rig and a very different hull form with a finer bow, higher ballast ratio, and its center of buoyancy moved further aft.

If I could afford to build a custom 38 foot design today, I would probably want less wetted surface, a slightly narrower beam at the deck line, more eliptical hull sections, a slighly narrower stern, a bulb keel, a larger fraction rig, a little more freeboard, a slightly lower house, better ventilation, a little larger fuel capacity (although I typically use about a tankful of fuel per year which is probably a good thing), a dedicated shower, maybe an aft stateroom instead of the double quarter berth. But then again for what I do and where I sail, the boat works great for me.

Jeff


----------



## PCP

kevlarpirate said:


> I also have a beef with statements about having great advancements after IOR , I say hogwash. Static curves for one got worse
> kev


Some knowledgeable information on IOR sailboats:

"Often accused of prohibiting great boats by encouraging mediocrity, the IOR &#8230;boats did not offer exciting performance off the wind, which was another reason for evolution away from the IOR.

..Peculiarities of IOR designs result from features that increase actual performance more than they increase IOR length, or other odd rules; IOR hulls bulge at girth measurement points; a reverse transom moves a girth measurement point to a thicker part of the hull; waterline length is measured while floating upright, so large overhangs are used to increase waterline sailing at speed; *the stability factor ignores crew, so IOR designers assume lots of live ballast*.

*&#8230; The IOR encourages high freeboard and high booms and prohibits keels wider at the bottom than at the top (bulbs). The IOR, in sum, encouraged heavy boats that lacked fair lines and clean hull forms.*

&#8230;..&#8230;. *The IMS *took the actual hull lines and analyzed their continuum, essentially eliminating funny bumps or hollows in the ensuing yachts and generally rendering much cleaner, faster lines *that were far more exciting, safer to sail*, ... "

International Offshore Rule - Wikipedia, the free encyclopedia

"While there is justifiable nostalgia today for the old IOR level rating of the IOR 1/4 ton. 1/2 ton and 1 ton class, change was necessary, as *the IOR could and did result in some unseaworthy boats being designed and built.*" 

Sailboat Handicap Rating Systems

Regards

Paulo


----------



## kevlarpirate

paulo , you are referring to the end of the IOR not the early seventies
But aside from that boats designed after that had worse curves.
like LPS of 105 deg.. laughable . Now stop with the disinformation. You are a hopeless romantic.


Jeff, You certainly study this, however I don’t believe 
These subtle differences provide more than slight performance 
advantages and all of them have their own set of compromises. 

You and some others slam the comfort formula but what gets me is you (they) don’t forward a definition of comfort. So therefore , until a definition is established, you have no right to criticize some ones work . My stand is comfort says that when weight and moment of inertia both in pitch and roll is decreased, higher accelerations are generated and that is not comfortable. 

I have listed a Farr 40 and a J40 , now there is a huge difference, the J-40 being noticeably more comfortable, however on a J-35 or an express 37, I would bet If you blind folded me and sailed me around I would have some difficulty knowing which boat I was on. In that performance bracket I may be able to detect the C&C ,which is actually 39 feet I believe, but I would not put money on that either. I do remember the cockpit of all those boats are uncomfortable and unacceptable for my standards.

Since the 70’s There are only two big design changes in these newer boats. The most popular boat which launched the new design trend was the J-35, and that trend is weight reductions and wider transoms, makes for faster off wind speed. That design trend was nothing new , it was no breakthrough development. All it amounted to was extending dinghy design into bigger boat design. No different than Mark Soverel extending surfboard lines into sailboat hulls , just big dinghys like a 60 year old Flying Dutchman …..
. Racing here and everywhere is downwind . No one except myself and some other lone wolves where ever they exist want to race up wind. 

As for comfort, meaning to me, among a few other things is being able to cut a wave in half without bracing myself ; big and heavy wins. If you like to shoot through or over the top of a wave fine, but if you call that comfortable, then you will have to redefine what comfort actually is. Comfort is low accelerations in my book and that is also the criteria for the 
Comfort index formula we are arguing. The math in the comfort index supports low accelerations and also statistical data of wave mass vs: boat mass. 

I will close with saying I have sailed 50 or so boats up to the C&C 61 Sorcery by far the most comfortable , My Ericson 46 rating second, and more comfortable than a Swan 46 because I don’t pound, same for Baltic 48 and way more comfortable than a SC 50. I won’t tolerate pounding. These boats today have no forefoot They track miserably , and wear out autopilots, pound pound pound 

One thing I don’t do is confuse comfort with excitement, like you Paulo
A last note , cruisers spend a lot of time on anchor. That’s important too.
Paulo, you are dreaming if you think those boats are quiet below.
You can pull the sales job on your wife all night, and in the end when she forgives you, You can at least name the boat “Love is blind”

I say your comfort argument It is a joke, just brainwashing yourself magnifying tiny variations into a feel good.

Mass and moment wins hands down , the formula is good

Now i am off for 4 days to split some waves in two, You guys can carry on 
in bliss.

Oh Paulo , how are you doing with the curves ?? 

I have a few more names by the way :

Fanny Slapper, Black and Blew, knuckle pounder, Midnight serenader

Now jeff, don't get in a puff, Paulo and you are all big guys now.


----------



## kevlarpirate

BTW Paulo 

The J-35 needs all 1650 lbs crew allowance to make it's numbers 
so much for your IOR data.
The newest boats today need rail meat, they do nothing but sit and switch sides. THE SC 50 needs 12 on the rail 
Who are you kidding ??

The pot should not call the kettle black


----------



## Jeff_H

Back in Post 73 I proposed a definition of a boat that offered desireable moion comfort. I suggested that a boat design that had desirable motion comfort characteristics would be a boat met some basic criteria in terms of balancing the shape of the boat (bouyancy distribution) and the weight distrubution within the boat so that the boat minimized both the amount of motion and the acceleration/ decceleration felt by the crew. 

And we agreed in principal that the amount and rate of change in speed of motion that a boat experiences is related to the amount of energy that is imparted into the boat, the ability of the boat to store that energy, and the ability of the boat to dampen (disburse) that stored energy. A design that offered comfortable motion would be one that attempted to moderate these sometimes contradictory factors.


----------



## kevlarpirate

Yes Jeff remember your post, and I agree in the details you have 
enough variables to play with and agree with your approach and 
that your concepts are in the right direction I also see you are not just going to buy into anything that is not vigorously challenged and analyzed. 

however, I would pose the question of 
how this optimization, which I would refer to as 2nd and 3rd order effects,
weight and moment being the first order effect,, anyway I would ask 
how far the 2nd and 3rd order effects get buried in the randomness
of a developed sea. 

Could you actually detect these more subtle design changes out there?
What may be clearly detectable on smoother water with lets say a 
steady chop, both direction and amplitude. This is just a thought.

Don't get me wrong, I believe designs can be optimized for particular venue
and purpose, and so I say new "designs" are evolved for down wind speed.
That sells. 

In your boat upgraded design which you propose, I don't think you have 
anything in mind other than performance to satisfy your own requirements.
So you are not designing it for some profit volume incentive and therefore compromise to that end. example of that approach would be Bose speakers.



I can give an example of my venue application here. 

We sail out of LA Harbor to Catalina Island regularly with our club members
and land a few miles to the west of the Isthmus , so it is an upwind climb 
and if you get off the dock after 12 noon, you are in for a rough ride. 
Making it on one tack you will be going up in six foot, some 7 foot breaking
and now and then a set of 8's. This is hard on the wind with the skirt inside 
if you can do it. This goes on for a good 3 hours. Summertime afternoon winds develop a short wavelength rugged chop with breaking tops.

The option is to this is leave earlier and motor in no wind, maybe get an hour of sailing in. or crack off put in a few hitches, and get there at dark

To give an example , on my 41, all my sheet lines hung up in the forepeak
with clove hitches ended up in a heap on the sole. Even I was pounding on the big ones.
and my foredeck soaking wet. But in the end it was still fun, and in the cockpit , we were quite dry and having fun. We also have the gloating feeling that when we take a mooring can, we did this in one tack, most boats won't or just can't. We keep our gloating to ourselves however. 

Anyway, this is the type of sailing I expect a boat can do and still be balanced and not get beat up.
OK now I have to go, cheers


----------



## PCP

kevlarpirate said:


> paulo , you are referring to the end of the IOR not the early seventies
> But aside from that boats designed after that had worse curves.
> like LPS of 105 deg.. laughable . Now stop with the disinformation. You are a hopeless romantic.
> ....


You say seventies? Boats in these days were not changed every two year's. Most of them were raced for many years. Many boats from the early 70's and mid 70's were racing on the 1979 Fastnet.

Take a look at what they say about IOR boats of that time and also to the large improvements that the IMS brought (over IOR) to the design of better and safer sailing boats.

Jeff as been saying that, I am saying the same, it looks everybody agrees on this...except you.

"In the infamous 1979 Fastnet race, 5 boats sank, 24 boats were abandoned, and 15 lives were lost. *This tragic loss was largely attributed to the "tortured" hull forms that had arisen out of designers' attempts to manipulate key IOR measurement points and to the relatively low ultimate stability of the latter generation IOR yachts *in comparison to traditional sailing yachts of the time and even those of a few rule-generations earlier.

*Designers had carried rule-beating to the extreme of producing less seaworthy yachts.*

What followed was the development of the VPP (Velocity Prediction Program) which would be used as the basis for the current IMS/ORC. The VPP that formed the basis of* IMS *arose out of the Irving Pratt Ocean Race Handicapping Project undertaken at MIT by J.E. Kerwin et. al.,* and was a monumental step forward for the sport as a whole*."

Untitled Document

The CCA's Technical Committee joined forces with the Technical Committee of the Measurement Handicap System to see what caused the Fastnet disaster. Several experts in the field of yacht design and marine engineering became central players in a study that was to last for five years. Karl Kirkman, chairman of the Sailboat Committee of the Society of Naval Architects and Marine Engineers, yacht designer Olin Stephens, Richard McCurdy, Chairman of the Safety At Sea Committee of the United States Yacht Racing Union, and Dan Strohmeier, who was a former president of SNAME, all undertook the various tasks of analyzing the design attributes, weather attributes and safety preparations. The primary focus of the study was to determine how and why so many boats capsized.

In 1985 a final report was issued by USYRU and SNAME's Joint Committee on Safety From Capsizing. The 66-page document, which is available from the United States Yacht Racing Union (P.O. Box 209, Newport, Rhode Island 02840), details the research undertaken by the joint committee and offers several broad conclusions that help illuminate what is safe and what is not in hull and yacht design. While the focus of the work was primarily to assess the capabilities - the likelihood of capsize - on boats designed under the various racing rules, IOR, IMS and the old CCA rule, the conclusions should affect the way all sailors think about design.

*The conclusions of the report, in brief, are:*
&#8230;&#8230;&#8230;&#8230;&#8230;&#8230;&#8230;&#8230;&#8230;&#8230;&#8230;&#8230;&#8230;&#8230;&#8230;&#8230;&#8230;&#8230;&#8230;&#8230;&#8230;&#8230;&#8230;&#8230;&#8230;&#8230;&#8230;&#8230;&#8230;&#8230;&#8230;&#8230;&#8230;&#8230;&#8230;&#8230;&#8230;&#8230;&#8230;&#8230;&#8230;&#8230;&#8230;&#8230;&#8230;&#8230;&#8230;&#8230;&#8230;&#8230;&#8230;&#8230;&#8230;&#8230;&#8230;&#8230;&#8230;&#8230;&#8230;&#8230;&#8230;&#8230;&#8230;&#8230;&#8230;&#8230;&#8230;&#8230;&#8230;&#8230;&#8230;&#8230;&#8230;&#8230;&#8230;&#8230;&#8230;&#8230;&#8230;&#8230;&#8230;&#8230;&#8230;&#8230;&#8230;&#8230;&#8230;&#8230;&#8230;&#8230;&#8230;&#8230;&#8230;&#8230;&#8230;&#8230;&#8230;&#8230;&#8230;&#8230;&#8230;&#8230;&#8230;&#8230;&#8230;&#8230;&#8230;&#8230;&#8230;&#8230;&#8230;&#8230;&#8230;&#8230;&#8230;&#8230;&#8230;&#8230;&#8230;&#8230;&#8230;&#8230;&#8230;&#8230;&#8230;&#8230;&#8230;&#8230;&#8230;&#8230;&#8230;&#8230;&#8230;&#8230;&#8230;&#8230;&#8230;&#8230;&#8230;&#8230;&#8230;&#8230;&#8230;&#8230;&#8230;&#8230;&#8230;&#8230;&#8230;&#8230;&#8230;&#8230;&#8230;&#8230;&#8230;&#8230;&#8230;&#8230;&#8230;&#8230;&#8230;&#8230;&#8230;&#8230;..
*Some modern boats, which have been designed to the IOR, &#8230;. may remain inverted following a capsize. *
&#8230;&#8230;&#8230;&#8230;&#8230;&#8230;&#8230;&#8230;&#8230;&#8230;&#8230;&#8230;&#8230;&#8230;&#8230;&#8230;&#8230;&#8230;&#8230;&#8230;&#8230;&#8230;&#8230;&#8230;&#8230;&#8230;&#8230;&#8230;&#8230;&#8230;&#8230;&#8230;&#8230;&#8230;&#8230;&#8230;&#8230;&#8230;&#8230;&#8230;&#8230;&#8230;&#8230;&#8230;&#8230;&#8230;&#8230;&#8230;&#8230;&#8230;&#8230;&#8230;&#8230;&#8230;&#8230;&#8230;&#8230;&#8230;&#8230;&#8230;&#8230;&#8230;&#8230;&#8230;&#8230;&#8230;&#8230;&#8230;&#8230;&#8230;&#8230;&#8230;&#8230;&#8230;&#8230;&#8230;&#8230;&#8230;&#8230;&#8230;&#8230;&#8230;&#8230;&#8230;&#8230;&#8230;&#8230;&#8230;&#8230;&#8230;&#8230;&#8230;&#8230;&#8230;&#8230;&#8230;&#8230;&#8230;&#8230;&#8230;&#8230;&#8230;&#8230;&#8230;&#8230;&#8230;&#8230;&#8230;&#8230;&#8230;.
*The lessons learned from the 1979 Fastnet cast a pall over the design evolutions of the IOR. *

The work done by the Joint Committee on Safety From Capsizing is a monument to the thought that has gone into yacht design during the 1980s.

The outcome has been a consensus among the leaders in naval architecture, in race organization and among the leading boat builders.

*At the beginning of the 1990s, sailors looking for suitable, safe boats in which to go to sea inherit the benefit of all the thought and work that has taken place.*

*New boats coming into the market are being conceived to be stable in bad weather, to be sea kindly and to be rigged for short-handed sailing. Safety, although not heralded by boat builder's promotion or by the sailors, is the big winner.*

*And, as the IOR slowly fades away, to be replaced by the IMS, sailors around the world will find ever increasingly that boats brought to them by designers and builders conform to the latest and best thinking in the safety at sea category*.

Choosing a Safe Sailboat | features.boats.com

Regards

Paulo


----------



## cormeum

PCP said:


> Choosing a Safe Sailboat | features.boats.com
> 
> Regards
> 
> Paulo


Interesting article-

Seems like for safety and easy motion they favor 
long
Skinny
Deep 
full keel
attached rudder
Now I wonder what rule produced those boats. :laugher


----------



## PCP

cormeum said:


> Interesting article-
> 
> Seems like for safety and easy motion they favor
> long
> Skinny
> Deep
> full keel
> attached rudder
> Now I wonder what rule produced those boats. :laugher


Interesting article, I agree with you on that. But it is truly amazing that you have concluded that George Day is defending Skinny, Deep, Full Keel, attached rudder, as the ideal cruising boat for all cruisers.

The article is so good that I will post the most significant parts. Please read it again, and have in mind that I have nothing against that kind of boats. If I don't particularly like IOR boats, I like very much the typical fast cruiser from the 30's to the 60's.

"*Choosing a Safe Sailboat*
*Finding the right boat for you and your family *

The choice of a boat in which to sail and cruise depends on many factors. *Boats are in many ways emblems of ourselves. They reflect our sense of taste, our affluence, our experience and, most importantly*, our plans for where and* how we will sail*&#8230;&#8230;

*Sailing should be fun *and owning a boat is a large part of that fun. Choosing a boat that *suits you* *and your family should place the notion of fun high on the list*&#8230;&#8230;

The trend to light, fast hulls that has dominated cruising and racing boats since the late 1960s, has provided sailors with boats that offer a high level of performance and ample accommodations. The evolution of hull design from full keels with keel-hung rudders has been a function of building materials and engineering as much as it has been due to innovation on the part of designers.

In the 1880s Nathaneal Herreshoff, the Wizard of Bristol, developed what may be the first small sailing vessel with a fin keel and spade rudder. He discovered that the performance of such a hull configuration outperformed every other design option of the time. Yet, a split keel and rudder did not find its way into wide use until the advent of fiberglass materials and the engineering made possible by the material.

Traditional boats of today, boats with full keels, keel-hung rudders and their propellers in an aperture, are descendants of working craft from a hundred years ago. The design is noted for its sea kindliness, it's ability to carry heavy loads, and its slow and deliberate motion through the water. The design type evolved at a time when all boats were built of wood. The simple engineering dictates of constructing a seaworthy sailing vessel in wood led designers and builders to craft the full-keel designs we know today.

In fact, the reason Nathaneal Herreshoff's early fin keeler did not lead to similar designs in larger, ocean going vessels was simply because the materials required to make such a vessel strong, seaworthy and safe did not exist at the time.

Yet, small boat design quickly followed Herrshoff's lead. ... But it was not until the l960s that larger boats, ocean sailing boats, could be engineered safely using the split design type.

William Lapworth's *Cal 40*, designed in the early 1960s, led the way by acquitting itself as a very fast sailing boat around the buoys, a winner of offshore races and, importantly,* a safe and sea kindly vessel.* The design of the Cal 40 was made possible by *the extraordinary strength and forming abilities of fiberglass construction. The material permitted imaginative designers to seek new ways to make sailboats go fast, and new ways to combine speed and comfort*.

The concepts behind the split keel and rudder design type gained even more notoriety and popularity when Olin Stephens created the successful America's Cup defender Intrepid. Unlike her competitors in that season, Intrepid had a stubby fin keel, a bustle under the after quarters and had her rudder mounted at the end of the bustle well aft. Intrepid was unbeatable.

The success of the Cal 40 and of Intrepid *opened many designer's and builder's eyes to the performance advantages of the fin keel, spade rudder design type*. *It was not long after that such designs became the standard, both among modern cruising boats *and the racing fleet.

There is little argument today that the split keel and rudder configuration produces boats faster than configurations of the more traditional type. If speed is the first prerequisite in a boat, then lightness, minimum wetted surface and a spade rudder/fin keel design is the way to go. Yet, for those who will be sailing in conditions other than pure drag racing around the buoys there are other considerations that must go into the selection of the right boat.

The sailor who is contemplating sailing long distances along a coast or making offshore passages must look for design qualities that enhance seaworthiness, stability, the ability to carry the loads of gear, water and fuel and the ability to be handled by a small - often two-person - crew, as well as speed through the water&#8230;&#8230;

The lessons learned from the 1979 Fastnet cast a pall over the design evolutions of the IOR. The work done by the Joint Committee on Safety From Capsizing is a monument to the thought that has gone into yacht design during the 1980s. The outcome has been a consensus among the leaders in naval architecture, in race organization and among the leading boat builders.

*At the beginning of the 1990s, sailors looking for suitable, safe boats in which to go to sea inherit the benefit of all the thought and work that has taken place. New boats coming into the market are being conceived to be stable in bad weather, to be sea kindly and to be rigged for short-handed sailing. Safety, although not heralded by boat builder's promotion or by the sailors, is the big winner.* And, as the IOR slowly fades away, to be replaced by the IMS, *sailors around the world will find ever increasingly that boats brought to them by designers and builders conform to the latest and best thinking in the safety at sea category*."

Choosing a Safe Sailboat | features.boats.com

Regards

Paulo


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## cormeum

> I like very much the typical fast cruiser from the 30's to the 60's.


Me too - that's why I bought one. 

here's the relevant parts:



> In 1985 a final report was issued by USYRU and SNAME's Joint Committee on Safety From Capsizing. The 66-page document, which is available from the United States Yacht Racing Union (P.O. Box 209, Newport, Rhode Island 02840), details the research undertaken by the joint committee and offers several broad conclusions that help illuminate what is safe and what is not in hull and yacht design. While the focus of the work was primarily to assess the capabilities - the likelihood of capsize - on boats designed under the various racing rules, IOR, IMS and the old CCA rule, the conclusions should affect the way all sailors think about design.
> *The conclusions of the report, in brief, are:*
> 
> Larger boats are less prone to capsize than smaller boats.
> A dismasted sailboat is more likely to capsize than a boat carrying her full rig.
> A boat has an inherent stability range, ie. an angle of heel past which it will capsize. That stability range can be calculated from the boat's lines and specifications.
> Some modern boats, which have been designed to the IOR, *or are designed to be particularly beamy, may remain inverted following a capsize.* Boats with a stability range under 120 degrees may remain inverted for as long as two minutes.
> Boats lying sideways to a sea, *particularly light, beamy vessels, *are more likely to capsize than boats that are held bow to the sea or stern to the sea. It follows, then, that boats that are sailed actively in gale conditions and breaking seas are more likely to avoid capsize than those left to lie untended, beam to the seas.


and here



> Traditional boats of today, boats with full keels, keel-hung rudders and their propellers in an aperture, are descendants of working craft from a hundred years ago. *The design is noted for its sea kindliness, it's ability to carry heavy loads, and its slow and deliberate motion through the water*.


and here



> There is little argument today that the split keel and rudder configuration produces boats faster than configurations of the more traditional type. If speed is the first prerequisite in a boat, then lightness, minimum wetted surface and a spade rudder/fin keel design is the way to go. Yet, for those who will be sailing in conditions other than pure drag racing around the buoys there are other considerations that must go into the selection of the right boat. *The sailor who is contemplating sailing long distances along a coast or making offshore passages must look for design qualities that enhance seaworthiness, stability, the ability to carry the loads of gear, water and fuel and the ability to be handled by a small - often two-person - crew, as well as speed through the water.*


Don't get me wrong, I'm not "dissing" IMS. It really was an improvement. Universal rule and CCA rule produced a lot of good sea boats too. (with very high AVS's as well as good sea keeping abilities)


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## PCP

kevlarpirate said:


> Paulo , forgot to mention, I said this before, but I sail my own boat
> at 15 to 17 degrees heel too. I can do it with whatever sail I choose to keep the boat at that heel. I get within 2/10 of my target speeds.


Of course you can. But I am not the kind of sailor (nor my family) that will sail a boat to 2/10 of its target speeds. With the cruising boats that are influenced by Open boats design, you can do 7/10 of the target speed with 17º of heel and 9/10 with 20º of heel. That is a huge difference in heel and in comfort.



kevlarpirate said:


> No one forces you to sail at 30 degrees heel. I agree if your boat is not easily driven , you may be forced toward that end of the envelope. But to actually have to do it is typically unnecessary and certainly not comfortable.


Here we agree. But that has not only to do with the boat being easily driven.
It was mainly to do with the way the boat gets the initial stability to sail.

On large transom boats (Open inspired) the initial stability comes from hull form, and there is a lot of it at small angles of heel. On a narrow boat, initial stability comes mostly from the righting moment provided by the keel, when the boat is heeled, and it is needed a lot of heel for that force to be enough to provide the necessary initial stability for sailing at speeds near the boat potential (30º heel).



kevlarpirate said:


> You may ask however , how one of these boats you want so much would behave if you were forced to sail at 30 degrees. You may find them unmanageable. Something I don't have to be concerned with not having a wide transom. Did you say that could be handled with twin rudders? (chuckle)


That is ridiculous. Yes, most of them have twin rudders and they are very stable going upwind. They will point less than 5º than a traditional cruiser racer, but have more sail power available (more initial stability) and can go faster at 40, 45º of the wind.

Regards

Paulo


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## cormeum

PCP said:


> On a narrow boat, initial stability comes mostly from the righting moment provided by the keel, when the boat is heeled, and it is needed a lot of heel for that force to be enough to provide the necessary initial stability for sailing at speeds near the boat potential (30º heel).


yeah, that sounds about right.


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## PCP

cormeum said:


> Me too - that's why I bought one.
> 
> ...
> 
> Don't get me wrong, I'm not "dissing" IMS. It really was an improvement. Universal rule and CCA rule produced a lot of good sea boats too. (with very high AVS's as well as good sea keeping abilities)


I agree with all of it. What he is saying is that there are a lot of personal choices you have to make. There are a lot of diferent types of boats that are seaworthy and the comfort and the way you like to sail, the way you have fun and enjoy sailing, is a personal choice.

In the last post you were saying that :

Seems like for safety and easy motion he is favoring favoring long Skinny Deep full keel attached rudder. Well, those too, but not only those.

Regards

Paulo


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## cormeum

PCP said:


> I agree with all of it. What he is saying is that there are a lot of personal choices you have to make. There are a lot of diferent types of boats that are seaworthy and the comfort and the way you like to sail, the way you have fun and enjoy sailing, is a personal choice.
> 
> In the last post you were saying that :
> 
> Seems like for safety and easy motion he is favoring favoring long Skinny Deep full keel attached rudder. Well, those too, but not only those.
> 
> Regards
> 
> Paulo


I agree with that.


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## PCP

Cormeum, (what is your first name?),

I could easily fall in love with one of these:









The photo was taken by my, last year in Porto Conte, Sardinia. We were anchored near by.

They are pure beauty to my eyes. They heel a lot, but who cares, love is irrational (my wife find them also beautiful). It is not the fastest type of boat around, but I am sure that sailing it would be very agreeable. But putting one of those in tip-top condition and maintaining it like that, would be out of my league.

Regards

Paulo


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## kevlarpirate

Paulo are you actually serious with your 2/10 of target remark?
Please re read my statement 

When I say I come "within" 2/10 that means if my target says I should be 
making 8 knots with 16 kts true wind at 50 degrees, getting "within" 2/10
means I will be making 7.8kts 

Do you actually think I would only be doing only 2 kts? meaning 2/10 "of" 8kts?

You mention:

"With the cruising boats that are influenced by Open boats design, you can do 7/10 of the target speed with 17º of heel and 9/10 with 20º of heel. That is a huge difference in heel and in comfort."

3 degrees is a "huge" difference heel and comfort??
You just said these boats are optimized for that heel, then why are they not doing 100% of their targets?

Not only are you not technical and obviously can't properly interpret a static curve, you attempt to school me and quite frankly 
you sound like you have not gotten beyond a sales brochure.


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## kevlarpirate

Regarding these wide transom boats that sail on their leeward chine , 
I guarantee you they will not repeat NOT sail with 30 degree heel.
unless they have twin rudders, I have purposely overpowered my boats
to over 40 degrees, and it remained balanced and manageable.

You can never do that and I dont care if you have 4 rudders. 
You need to sail one of these or at least talk to an owner.

Then you say this " That is ridiculous. Yes, most of them have twin rudders and they are very stable going upwind. They will point less than 5º than a traditional cruiser racer, but have more sail power available (more initial stability) and can go faster at 40, 45º of the wind."

This statement makes no sense at all.

your continued digging up opinion defending these downwind race boats and theorizing these designs make for comfortable and safe cruising boats is simply foolish.

At least you should admit the compromises and stop selling these highly compromised designs to others . We all know you are sold hook line and sinker, you should leave it at that .

You also have never approached the FACT that after the IOR , static curves got worse , You continually duck this question. 
The Hanse 430 curve is as bad as the worst of the late IOR curves.

The high righting arm is because it is a larger boat. It rolls off early into the danger zone. What that means is it will snap roll to a beam sea and very likely dig it's leeward rail on a big beam wave.

Wide transoms are needed for heavy air down wind work, we all know that 
Foe cruising purposes where likely you are depowered, that wide transom becomes a liability.


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## PCP

kevlarpirate said:


> Paulo are you actually serious with your 2/10 of target remark?
> Please re read my statement
> 
> When I say I come "within" 2/10 that means if my target says I should be
> making 8 knots with 16 kts true wind at 50 degrees, getting "within" 2/10
> means I will be making 7.8kts
> 
> Do you actually think I would only be doing only 2 kts? meaning 2/10 "of" 8kts?


Yes, you are right, I misunderstood what you have said. But what you have said and are still saying doesn't make sense.

In a boat like yours, that has a soft stability curve, the difference between 20º of heel and 30/35º roughly corresponds to 1/3 of the righting moment that is used for sailing. That is, about 1/3 of the boat "sailing power".

Pretending that 1/3 of the power will only bring the boat from 7.8 to 8.0k is absurd. You know, I sail, members of this forum are sailors, we have boats and we know that on most boats (boats designed to offer the best performance at 30º of heel) a difference of 10º of heel (and the sail power needed to accomplish that) will translate in much more than 0.2k, as you say.

In my old boat, that would be translated in about 1.5K. Of course, we are talking about sailing upwind.

Three weeks ago I have said to you:

*"Post those curves of old boats that are "far superior" and we can talk and see about that."*

And you have replied:



kevlarpirate said:


> Not hard at all, My Performance Package is on board , I can scan it
> or take dig photos and send as jpeg i guess.
> It is not a massaged curve either like some do in hopes of getting a
> category 0 or 1.
> ......
> I will need a day or so, will see the boats tomorrow, so in the meanwhile , why don't yo do some reading since now I am working for you here . then we can amp it up a bit , if you like.
> .....Kev


Three weeks later I am still waiting for the Ericsson 46stability curve. Post it, as you have said, and I will show you that the difference in righting moment between 20º and 30/35º of heel roughly correspond, in your boat, to about 1/3 of the "sailing power".



kevlarpirate said:


> You mention:
> 
> "With the cruising boats that are influenced by Open boats design, you can do 7/10 of the target speed with 17º of heel and 9/10 with 20º of heel. That is a huge difference in heel and in comfort."
> 
> 3 degrees is a "huge" difference heel and comfort??
> You just said these boats are optimized for that heel, then why are they not doing 100% of their targets?


Here it is you who is misunderstanding me. I am comparing the comfort in sailing at 17º or 20º, close to the boat potential, with the comfort of sailing a boat that will only go near its potential near to 30º.

Of course, I am being honest talking about 7/10 and 9/10 of the boat speed potential (upwind) at 17º and 20º of heel, in a large transom boat, optimized to sail at 17º of heel. I don´t think we can say the same about you, when you talk of a having 8/10 of the speed potential (upwind) at 20º of heel, in a boat optimized to sail at 30º of heel. That's a 0.2k difference

Regards

Paulo


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## kevlarpirate

Paulo,.

I take data continually with calibrated instruments, everyone is calibrated 
I regularly make the numbers I post. I live for taking data and pursuing closure between theory and practice. This is what we engineers live for,
how we were born
so I would appreciate you not attempting to call me a liar. 
Your assumption that heel and speed are linearly related only confirms the fact that you are not technically qualified to participate here, yet you persist.

The heel to speed relation is NON LINEAR. just like having to triple or quadruple the horsepower to just double the speed of your car.

You are constantly confused because you don't read thoroughly.
I left a trap and you failed. I said 2/10 of 8 kts was 2 ..... And it is not 
It is 1.6 kts and that passed right over your head.


I did not post my curve because the Jpeg would not upload , for what ever reason , doesn't matter , you never responded until now, but I will do it again , just to show others what a healthy curve should look like.


I will post the data at my convenience, but aside from that I cannot converse with non technical people.


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## PCP

kevlarpirate said:


> &#8230;&#8230;
> Paulo, are you still working on the answer to the static curve question? (chuckle)





kevlarpirate said:


> Oh Paulo , how are you doing with the curves ??
> I have a few more names by the way :&#8230;&#8230;.
> Now jeff, don't get in a puff, Paulo and you are all big guys now.





kevlarpirate said:


> Paulo ,
> It has now become apparent to me that you do not know how to interpret the static curves, I am concluding you have it totally backwards.
> re: post #28, to allow me to understand your thinking , could you evaluate the differences between the Hanse 430 and the 36 foot Bavaria? just those two. OK?
> kev





kevlarpirate said:


> Not only are you not technical and obviously can't properly interpret a static curve, you attempt to school me and quite frankly
> you sound like you have not gotten beyond a sales brochure.


Well, I would not have the trouble to analyze a stability curve for you (after all I am still waiting for the Ericsson 46 stability curve that you have said you were going to post, three weeks ago), but since I have done that already more than two years ago, and it can be interesting information to the forum, I will post it.

Of course, you have to remember that I am polite and I was on that forum (their forum) looking for information about the Hanse 430. The last thing I wanted was to be rude, or to say bad things about their boats, so I was "gentle" in a way I addressed the Hanse 430 stability. I have to say that I have also some doubts about that stability curve, but that is another story.









"I am not saying that the boat has not a good potential for speed (much more than the Oceanis) I was saying only that the Hanse 430 has an unusually big inverted stability and I am not saying that based on almost meaningless data but on the stability curves provided by the manufacturers, the ones that are used for certifying the boat.

Those curves are pretty close to reality and if there is some difference is for worse, because they don't take into account the weight of the furling sails and radar.

The ones I am posting are RM curves (moments), they are in T/m and all boats are in maximum charge condition, except the Bavaria 36 that is on minimum sailing charge condition.

I have made this graphic for making a personal evaluation of the Hanse 430 stability compared with some of the boats I am considering. I didn't consider the Oceanis 43 because I prefer the other two and because it would give me more work, but the Oceanis 43 stability curve is not very different than the one from the Jeanneau 42.

I have considered the RM 1200, the Jeanneau 42 and the Hanse 430. The Bavaria 36 serves as a measure in what regards inverted stability.

The overall best curve is the one from RM 1200. It is only a 40ft and the lighter of the three boats (7,8T against the Hanse's 10,4T) but it manages to have only less 4% of the Hanse's positive stability and 93% less negative stability. The negative stability of the Jeanneau is similar to the RM's.

The Jeanneau and the RM have not a particularly good inverted stability (they are too stable for my taste), I would say they are slightly below average, they cannot compare with the inverted stability of a Malo 43, a Finngulf 41 , a Wauquiez 45 or a J 133. Comparing with the data I have seen about the issue, I would say that while the last ones would right themselves up (giving a sea condition capable of rolling them) in about 30 s the Jeanneau and RM would need an average time between 1 and three minutes.

For the Hanse 430&#8230;the energy needed to overcome that huge inverted stability is bigger than the one needed to invert the Bavaria 36 (1,2 X). The Bavaria 36 is a class A boat and that means that it can stand 7m waves. There are several that circumnavigated and several that have been caught in storms without being rolled.

Of course, for inverting the Hanse 430 (from a 0º heel position) you need two times more energy than the one needed to roll the Bavaria 36, but that is not true if the boat suffers a broach and comes to 90º of heel.

If both boats are at 90º of heel you need more energy to invert the Bavaria, comparing with the one needed to invert the Hanse. That's why I was saying that you should take a lot of care if you decide to carry a lot of sail in bad weather (racing).

I could have said nothing. I have already taken away my doubts but I believe that sailors should know how their boats behave even on those situations that almost never happen. If you know your boat you know how to act, even in extreme conditions&#8230;and after all the Hanse 430 has also a big positive stability&#8230;just keep it upright if there are waves."

myHanse - Hanse Yachts Owners Forum: Polar diagram for 430 ?

Regards

Paulo


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## PCP

kevlarpirate said:


> Paulo,....
> 
> You are constantly confused because you don't read thoroughly.
> I left a trap and you failed. I said 2/10 of 8 kts was 2 ..... And it is not
> It is 1.6 kts and that passed right over your head.


 Sometimes you are confusing, but this time you were clear. You were saying that at 17º degrees of heel your boat would do 7.8K and with more sail, heeled at 30º you would do 8k. A difference of 0.2k for 13º of heel.



kevlarpirate said:


> ..at 15 to 17 degrees heel too. I can do it with whatever sail I choose to keep the boat at that heel. I get within 2/10 of my target speeds.





kevlarpirate said:


> *When I say I come "within" 2/10 that means if my target says I should be
> making 8 knots with 16 kts true wind at 50 degrees, getting "within" 2/10
> means I will be making 7.8kts *


I have said:



PCP said:


> But what you have said and are still saying doesn't make sense.
> 
> In a boat like yours, that has a soft stability curve, the difference between 20º of heel and 30/35º roughly corresponds to 1/3 of the righting moment that is used for sailing. That is, about 1/3 of the boat "sailing power".
> 
> Pretending that 1/3 of the power will only bring the boat from 7.8 to 8.0k is absurd. You know, I sail, members of this forum are sailors, we have boats and we know that on most boats (boats designed to offer the best performance at 30º of heel) a difference of 10º of heel (and the sail power needed to accomplish that) will translate in much more than 0.2k, as you say.
> 
> In my old boat, that would be translated in about 1.5K. Of course, we are talking about sailing upwind.
> 
> Paulo


So, no you are saying that I am right, that the difference in speed between 17º of heel and 30º (upwind) is 1.6k (I was saying 1.5K while you were saying 0.2K) and the way you say it is : *"I left a trap and you failed"*

You are an interesting guy .

Regards

Paulo


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## kevlarpirate

Again you persist with numbers with no backing in addition to your assumptions.

my polar diagrams or any for that matter are NOT repeat NOT based on any 
set heel angle. Again you don't study these things.

My highest heel for any one target is 28deg and that is the 20kt curve and the BAW is somewhere around 120 deg if I remember right .
The earlier target speed 8 kt at 50 deg in 16kts. (UPWIND) and that heel is around 24 or so .. You are TOTALLY WRONG about the 1.6 kt 
when I say 2/10 I have data to back it 

Please quit with the assumptions, Another one you made is the energy to invert back to upright , Where on God's earth do you find these numbers?
you mention 1,2 X Look more closely at the curve , You are way off!

then you mention a factor of 2 ??? where did that come from????

integrating under the curve I see a factor of between 3 and 4


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## kevlarpirate

you may also be informed I have 12 headsails to choose from on my 41
and i have 6 on my E-46...so I generate a lot of data over the years.


I have probably used up another 12 over the years.


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## tdw

The acerbic nature of this thread is becoming quite tedious. 

Keep it civil.

Threads can quite easily disappear you know....and you wouldn't want to have that on your conscience now, would you ?


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## kevlarpirate

If Paulo loves this boat so much , then why doesn't he own one 
or any other which meets his needs. Then he can tell us about it instead of dreaming how the boat will behave. 

I listen to people who take data and can talk technical 
this conversation is vacuous. Time to end here


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## Iveywing

phboujon said:


> Hi,
> 
> I am making a short list of blue water boats (for a potential purchase and sabbatical) by looking at their ratios, and one of the criteria my girlfriend and I are trying to understand is the comfort ratio.
> 
> While I understand how it is calculated, and what is the overall meaning, I have no clue (due to being an inexperienced sailor, still taking sailing classes) what 5 to 10 points difference really make once blue water sailing.
> 
> Case in point (from online database):
> 
> Tayana 37 - CR: 43.8 -> Reference point (RP)
> Pacific Seacraft 37 - CR: 38.0 -> -5.8 of RP
> Cabo Rico 36 - CR: 35.6 -> -8.2 of RP
> Shannon 37 - CR:33.5 -> -10.3 of RP
> 
> My question isn't which boat is better, I am not there yet. What I'd like to understand is whether the differences between these boats, in term of motion comfort, can truly be perceived at sea? Is a Shannon 37 really less comfortable than a Tayana 37? Tayana 37 vs. PS 37? PS 37 vs. CR 36? etc... or am I paying too close attention to what is just a number?
> 
> None of the boats I am considering seems to be apart of more than 10-12 points on the comfort ratio. Should I be happy their comfort are in the 30-40 range and move on to care about other numbers / other issues?
> 
> Thank you for your help,
> 
> Cheers
> Philippe


FYI. Your delta between the Pacific Seacraft and the RP Tayana is actually -6.8 vs. -5.8. Moving on, there is more than just the CR to consider because it's also a question of how and where the weight is distributed to avoid hobby horsing. For example the 2018 Boreal 47 centralized it's fluid tanks over the keel area and the two water tanks either side of the keel stepped mast without restricted access to keel bolts, etc.. The windless was positioned aft of the bow and just ahead of the mast so that the chain can be stowed above the keel travelling down adjacent to the mast column without being seen in the cabin and keeping the weight of the chain out of forward chain locker. As such, all of the weight is low and centralized and makes for a very comfortable sea going vessel. This is much more important to consider than a +/- 5 or 10 point delta above or below a reference vessel, respecting your market is used vessels.


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## Jeff_H

As I posted back in 2010 when this tread was active, the Capsize Screen Formula contains none of the main factors which controls the likelihood of a capsize, and the Motion Comfort Ratio provides none of the critical factors which control motion comfort. 
The current science suggests that the primary factors are static and heeled weight and buoyancy distribution, waterline length, waterline length relative to length on deck, damping, and waterline beam (rather than beam on deck).

These formulas are so grossly inaccurate, as to be dangerously misleading. One example of why this is true is that these formulas have the impact of beam backwards. The current understanding is that beamier boats are less likely to capsize while the capsize screen sees beam as a negative.

Jeff


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## Iveywing

Thank you Jeff. Agreed and why I am still searching for the perfect beamy compromise. Regards, Jon


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## MoonBeamEstate

When someone is searching for the "perfect" solution I always think about this General Patton quote. Not much in our world it perfect. I sail an imperfect boat. I wonder if the OP from 10 years ago ever found his perfect boat. LOL
*"A good plan violently executed now is better than a perfect plan executed at some indefinite time in the future."*


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