# Something about the fractional rig that I just don't get...



## MedSailor (Mar 30, 2008)

There's a concept that's been bugging me about the factional rig. I understand the advantage of mast bend, but the smaller foresail is also touted as an advantage with the main being "the sail that does all the work anyway".

But, wasn't the big deck sweeping and overlapping headsail supposed to be the thing that really mattered? All the club racers have huge overlapping headsails and the "slot effect" is supposed to help with speed. I've heard people say that the headsail is the one that does all the work and pointing...










These guys are fast right? How come they look like masthead boats with big overlapping gennies?

MedSailor


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## Stumble (Feb 2, 2012)

The jibs are all fractional in that shot, Puma is sailing on a Code 0.


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## manatee (Feb 27, 2013)

Interesting discussion about the rigs *here*.


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## paulk (Jun 2, 2000)

I read something, somewhere (Marcaj?) about how the shape of a fractionally rigged mast and sail was closer to the optimal leading edge shape than a masthead rig. The fractional rig supposedly creates a "better" vortex off the sails, which means going faster with the same sail area. It seems that a curved, (or "jointed",as it is in a fractional rig) leading edge works better aerodynamically than a single straight line (as a masthead rig would have). Airplane leading edges are often swept back, perhaps for this same reason?


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## bobperry (Apr 29, 2011)

Med:
You have a lot of catching up to do. A lot.
Bend has almost nothing to do with it. Bend is more important on a masthead rig where you use bend to increase headstay tension and flatten the main. With a frac rig you get headstay tension with runners or swept spreaders. And, if you sweep your spreaders 20 or more degrees you are not going to be bending the mast much.

This of the rig as one big foil. The jib is just the leading edge.
With a big main and a small headsail you no longer have to change headsails for optimal performance, theoretically anyway. There are heavy weight jibs and light weights jibs but the LP will remain about the same.

The photo you posted is misleading. Only one boat is flying a masthead foresail and this sail is a code zero. It is not their working headsail. It is a reaching sail. The other boats in the pic clearly show frac rigs. Look closely.

Tomorrow I race FRANCIS. Big, tall frac rig and I will make it sing.

In the end we know that one, articulated wing sail is the best sail for speed. The frac rig comes close to replicating the "one foil" approach than does the masthead rig.


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## MedSailor (Mar 30, 2008)

From poster Ian McColgin on the wooden boat thread linked to:

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_Rating rules and fashion favor bigger jibs. Pity there's even such a thing as "free" sail area in the overlap past J and the high roach of some abaft the mast sails with huge full battens. While the fractional rig with small jib is probably the most efficient way to carve up some fixed pile of canvass, not to mention the fun of bending the mast to shape the sail a bit, there is much to be said for keeping a dead straight column and the structural simplicity of a masthead rig. _
--------------------------------

Does this help explain the deck sweeping 140+ genoas and masthead rigs that seem to dominate the racing I've been a part of?

MedSailor


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## paulk (Jun 2, 2000)

Good luck, Bob, though have you considered getting some new sails? Carbon ones might scare a lot of competition into making mistakes.


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## bobperry (Apr 29, 2011)

Med:
That guy has never sailed a modern frac rig. As I said in my post, with spreaders often swept to 30 degrees there is no mast bending to the degree it was some in old masthead IOR rigs.. You can bend the small top proportion if you want to but below the hounds the mast will be dead straight. I know becuase I design and sail these boats. I don't hypothesize or speculate. You can tune in a little pre-bend if you like. But once sailing there is little you can do with bending the mast. That doesn't always stop us from trying.

My Flying Tiger 7.5 meter.

My Flying Tiger 10 meter

ICON my all carbon 63' frac rigged lifting keel racer/cruiser


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## bobperry (Apr 29, 2011)

Med:
The other huge variable that I forgot to mention is modern sail fabrics.

The modern racing matrix type sail does not stretch the way dacron stretches. The shape you want is there from the get go. You can adjust halyard tension, outhaul and cunningham to increase the draft of the sail but you can;t stretch a modern sail with mast bend the way you could with a dacron sail.

Take a look at a modern racing boat in light air. You will most probably see creases in the luff. Years ago this would have been unheard of. But with modern fabrics that one of the few ways you can play with draft.

Like so many "advancements" it takes a combination of factors to make it all work together.


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## MedSailor (Mar 30, 2008)

Bob, 

I definitely see the merits of the fractional rig, and while I've heard a lot of people talk about mast bend on fractional rigs, I get what you're saying. Actually, the only sailor that I've ever sailed with that REALLY seemed to know what he was doing with mast bend and make it work in his favor is Doug on Night Runner. Damn I love that boat.... Skipper too. I've learned a lot from the few times I've sailed with Doug. 

I can see now about the flying wing shape of the mainsail, and how the rigid wind of some of the americas cup boats resembles one quite closely. Small headsails sound like a great thing to me too..... Basically, I'm sold on the factional rig concept in every way.

To phrase my question another way, what ARE the advantages of masthead rigs and big overlapping headsails? It seems like most of the "arguments for them", like the slot effect, and them being stronger, just don't hold up. Are they outdated tech? Racing rule beaters? Is the buying public just more "comfortable" with them?

MedSailor

PS I am very familliar with ICON. I used to live across the fairway from her at Shilshole, and when I moved up to Anacortes, she followed me up here. I admire her often, though usually from the stern....


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## bobperry (Apr 29, 2011)

Med:
I think we need to get a real sailmaker involved in this chat. We need to divide "efficiency" from "rule advantage".

Time marches on.
Things change.


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## Shockwave (Feb 4, 2014)

Then why is the mast head rig J29 faster then the frac rig 29, same with the Thomas 35 or even the J35 vs the J36? Hard to figure sometimes.


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## christian.hess (Sep 18, 2013)

hmmmmmmmm I like frac rigs...I like sailing and working the main

maybe its cause I like sailing dinghies...like lasers

hmmmmm


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## Stumble (Feb 2, 2012)

The downside to fractional rigs is that they often also have fractional kites. Which drastically reduce available sail area downwind and when reaching. Ideally you have a fractional upwind and a masthead down. But it takes a different mast than pure fractional since the runners don't support the upper tip, it's gets tricky to jibe and risks the mast

For cruising there is an argument to be made that a big overlapping jib is nice to have since they are better on a reach. But with asymetrics hitting the cruising market this is falling away.


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## bobmcgov (Jul 19, 2007)

I've read the claim that a fractional rig is not a masthead rig with a short jib; it is a masthead rig with a tall main. That is, think of the hoist above the forestay tang as free mainsail area. Plus, the taller rig buys you more roach area ahead of the backstay, all the way down. The stick on our Albin Ballad looks stumpy compared to many of today's frac-rigged boats -- because it *is*.

I wonder if having the top of the main operating in clean air isn't an advantage, too, close-hauled. Esp. in light to medium winds, the mainsail needs to be twisted off quite a lot to keep the angle of attack the same from bottom to top, when the wind at your Airex may be twice what it is at deck level and AWA is maybe 10 degrees farther abeam. The top of the main can be twisted off more than the top of the jib; on a masthead rig, that may choke the slot & cause lots of drag. Just speculating.


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## RichH (Jul 10, 2000)

The problem is that most of what has been published and routinely discussed, (even in US high schools) etc. on how sails (wings, etc) work has been wrong since the time when the Wright Brothers empirically discovered an entirely different reason for 'lift' (and such applies to all fluid dynamics - hydrodynamics as well as aerodynamics). Suffice it to say that such sciences are definitely NOT intuitive; yet, when using tell tales on sails or combinations of sails one can under exact conditions see the effect of air apparently 'circulating around' such sail and sail combinations.

Without getting into discussion of fluid dynamics and losing everyone via 'glassy eyed stares and nods', sails 'work' aerodynamically (going upwind) simply because the flow air has 1. 'friction' and 2. the apparent oncoming boat/sails causes some proportion of that airflow to go FORWARD on the windward side of the sails which in turn cause an 'upwash' way out in front of the boat causing a circulation effect of air flow. This is not dependent on whether the boat is mast headed or fractional rigged - its just the total area of the sails moving forward that causes effect ... and the effect is air circulating 'around' the sails/wing/propeller/turbine, etc. 
The seminal articles that 'unveiled' such strange behavior to the sailing community was introduced by Arvel Gentry (aerodynamicist and sailor) in the early 1970s. Do websearch for: airflow+sails+circulation
The same applies to all fluid flow about 'foils'.

http://ljjensen.net/Maritimt/A Review of Modern Sail Theory.pdf
https://cld.pt/dl/download/10d8878b...ht - The Aerodynamics Of Sail Interaction.pdf

Again, such fluid flow is *NOT 'intuitive'* yet once you begin to understand exactly what is happening, you can under the 'right' conditions see these effects when using a full set of tell tales (or smoke tracers) on sails/wings, etc. To reach such understanding you will have to ignore everything you previously ever learned about how wings and sails 'work'. Under the 'right' conditions when sailing aerodynamically, usually when the air speed flow is exactly matching the forward speed of the boat/sails, you will notice that the windward side tell tales will not be streaming aft but will be streaming FORWARD ( a vectorial SUM) !!!!!! ... streaming forward on the windward side and streaming aft on the leeward side --- the 'total' flow is 'circulating' around the sails and in so doing is causing an optimum amount of 'upwash' well out in front of the boat/sails; hence the ability to 'point' (and point higher, etc. than when attempting to explain or rationalize by the 'wrong' and long held theories). The 'upwash' is simply air moving out of the way of the oncoming boat/sails and moving aside towards the apparent 'lower pressure' (leeward) side and long before it gets even close to the boat/sails. The windward side of the sails moving forward is causing 'some' of the air on the windward side to flow FORWARD .... its simply caused by the square foot of sail / wing material moving forward and doesnt matter if its all held up by a masthead rig or a fractional rig ... its 'just' the amount of sq. ft. of area moving forward. The 'keys' here are twofold: 1. air flow is 'circulating' around sails and 2. air has viscosity (friction).

A lot of articles and reply commentary have been written about 'sails and their recirculation flow regimes'. Do a websearch but be warned that some of the aerodynamic theory will be difficult to understand, .... at least on the first few readings. If interested, do read and reread and reread again such articles several times and then transfer that knowledge to YOUR sails with telltales installed .... you will eventually state "oh yeah, I think I can SEE what is happening; but, you have to have a full set of tell tales and 'gentry tufts' installed to see this. 
Your high school science teacher was entirely WRONG about wings and sails and propellers, and what causes 'lift' etc.

;-)


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## christian.hess (Sep 18, 2013)

Ive always had a bad time with tell tales...or better put I never completely use them, rather I go by speed and and wether Im luffing or not to get best angle and speed...etc...

its interesting when you say all this rich and It kind of resonates with me cause I pay too much attention to certain things...and just going by telltales alone never worked for me...

I too have noticed the windard tell tales point STRAIGHT up and Forward on many occasions trying to determine what was actually happening...juduging speed, heel, angle etc...


in the end I use many ways to trime sails versus just one way, use all methods to be better etc...

peace


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## capt vimes (Dec 2, 2013)

RichH - i think you missunderstood the article...
I have not read the full article, but mr gentry speaks clearly of faster and slower airflow around an airfoil and thus creating a pressure difference which in turn produces lift...
Point 2.5 of the linked article.

What he did was introducing an circulation flow to simply model the airflow around an airfoil because the standard theories and models did not produce the right figures...
Pernouille is still valid and telltales on the leading edge of a sail may point forward because the airflow seperates there, producing vortices...
There is no circulation flow around a sail!


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## hellosailor (Apr 11, 2006)

Med-
Oddly enough I asked a similar question just yesterday. Logically, there should be no innate advantage in having a smaller shorter foresail, which suggests that all of the "logic" in favor of fractional rigs is based on bubbameisers. (Nonsense tales perpetuated by grandmas.)

So let's look at physics and ignore all the bilge myths.

What is different about the interaction of the sails (main and fore) when you have a fractional rig? Well, there's a vortex coming off the end of every wing and that turbulence creates drag. With a masthead rig, and the main and foresail both having their top ends in the same place, wouldn't those two vortexes reinforce and create extra drag, and a loss of lift on the top of the main?

Aha. Maybe, maybe not, but has anyone ever bought time in a wind tunnel and actually examined that? I don't know, I've never heard mention of it but I'm not into heavy reading of aerodynamic testing.

Now take the same two sails, and stagger them so the two tip vortexes do NOT intermingle and reinforce each other. What do you have? A fractional rig!

Maybe it could be that simple. Simple physics, which no one has bothered to document or examine in detail because "everyone knows" the fractional rig with less sail area magically is faster. Magically. Hmmm, maybe that way the vortex coming off the tip on the foresail actually increases the flow below the tip of the main, actually boosting the performance of the main as well?!

Or can anyone point us to some _objective _wind tunnel work on this?

" Argh, yes, cod be faster than whales, so that must be the right way to shape a hull."
Ahuh. And rotting meat generates flies. Nothing new under the sun.


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## Omatako (Sep 14, 2003)

I got glassy -eyed about here



RichH said:


> This is not dependent on whether the boat is mast headed or fractional rigged - its just the total area of the sails moving forward that causes effect ... and the effect is air circulating 'around' the sails/wing/propeller/turbine, etc.


and here



RichH said:


> and doesnt matter if its all held up by a masthead rig or a fractional rig ... its 'just' the amount of sq. ft. of area moving forward.


So none of this scintillating reading leads me to an understanding why a frac rig is better than a masthead rig. 

Or I missed something.


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## Omatako (Sep 14, 2003)

bobperry said:


> Med:
> You have a lot of catching up to do. A lot.
> Bend has almost nothing to do with it. Bend is more important on a masthead rig where you use bend to increase headstay tension and flatten the main. With a frac rig you get headstay tension with runners or swept spreaders. And, if you sweep your spreaders 20 or more degrees you are not going to be bending the mast much.
> 
> ...


Bob, whilst I unreservedly bow to your superior knowledge, it would be great for me to share some of it. Nothing in the post above leads me to an understanding of why/how a frac rig trumps a masthead rig.


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## Omatako (Sep 14, 2003)

bobperry said:


> Med:
> That guy has never sailed a modern frac rig. As I said in my post, with spreaders often swept to 30 degrees there is no mast bending to the degree it was some in old masthead IOR rigs.. You can bend the small top proportion if you want to but below the hounds the mast will be dead straight. I know becuase I design and sail these boats. I don't hypothesize or speculate. You can tune in a little pre-bend if you like. But once sailing there is little you can do with bending the mast. That doesn't always stop us from trying.


Ditto my response above. Please give me something I can believe in.


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## Omatako (Sep 14, 2003)

hellosailor said:


> So let's look at physics and ignore all the bilge myths.
> 
> What is different about the interaction of the sails (main and fore) when you have a fractional rig? Well, there's a vortex coming off the end of every wing and that turbulence creates drag. With a masthead rig, and the main and foresail both having their top ends in the same place, wouldn't those two vortexes reinforce and create extra drag, and a loss of lift on the top of the main?
> 
> ...


And finally someone comes up with a possible explanation. Thanks HS.

But I still have a problem believing that the mingled vortices at the top end of the main will create sufficient drag to over come the additional sail area of 140%, low footed, masthead genoa.

Strangely, I actually believe that a frac rig_* is*_ better because I cannot forget marvelling at the giant AC trimaran back in Valencia going to windward and dropping the headsail altogether and going faster.  Or the relatively tiny jibs on the AC foiling cats.

But still I haven't heard any compelling evidence to suggest this is true of a non-wing rig.

Maybe someone who designs and builds boats will take a frac rig and sail it for a month then change it to a masthead rig and sail it for a month and provide some real comparative data to prove the point. Then we would have something to believe in.

I will follow this thread with interest even though I have no intention of ditching my masthead rig.


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## Stumble (Feb 2, 2012)

Shockwave said:


> Then why is the mast head rig J29 faster then the frac rig 29, same with the Thomas 35 or even the J35 vs the J36? Hard to figure sometimes.


Simple, the J-29 MH has more sail area than the fractional downwind by about 10% thanks to a much bigger spinnaker flown from the top instead of at the fractional point. Based on standard PHRF rules if the FH switched to a MH kite it would be penalized 6 seconds making it 3 seconds faster than the MH.

While discussing why is beyond my knowledge base looking at boats that are limited in sail area but not sail plan I think are instructive. Those classes with just a sail area maximum have pretty much all switched over to high aspect cat rigs, those with main sail are maximums have high aspect mains and overlapping jibs, those with max main and max jib area use high aspect mains and high aspect non overlapping jibs.

What this indicates to me is that for the same sail area upwind the ideal seems to be a massive main. If you have to divide it up then add the smallest jib possible, finally if you have extra sail area you tack it on to a bigger jib.


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## capecodda (Oct 6, 2009)

I'm an engineer, but I skipped the fluids course, but now regret that.

As a cruiser, I like the fractional rig for practical reasons. Usually, the mast is further forward, allowing the boat to balance reasonably even with the jib rolled up. Small jib is easy to tack, a bigger fully battened main is easy to handle, you can hold a full jib into an increasing wind while reefing the main only (partially rolled jibs usually don't hold their shape well), the boat will sail to windward on main alone when short tacking allowing someone to easily work the foredeck to get the anchor ready or grab a mooring, and a furling code zero (a super easy to deploy light wind sail for cruisers) can be launched easily in front of the rolled up jib.

I read a little about Bernoulli and Reynolds numbers, but cannot remember any of it


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## bobperry (Apr 29, 2011)

Stumble makes a very good point. The basic modern frac rig is a much bigger rig than the masthead rig of 20 years ago. A typical SA/D today could be 21.00 while a typical SA/D of 20 years back could be 16.5.

Tako:
I'll give you something to believe in SA (and I don't mean Sail area). Yesterday we raced FRANCIS with it's tall frac rig and got a First to finish and a First in Corrected Time win. We did this with a crew of four on a 63'er. Believe in that.


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## RichH (Jul 10, 2000)

capecodda said:


> I'm an engineer, but I skipped the fluids course, but now regret that.
> 
> As a cruiser, I like the fractional rig for practical reasons. Usually, the mast is further forward, allowing the boat to balance reasonably even with the jib rolled up. Small jib is easy to tack, a bigger fully battened main is easy to handle, you can hold a full jib into an increasing wind while reefing the main only (partially rolled jibs usually don't hold their shape well), the boat will sail to windward on main alone when short tacking allowing someone to easily work the foredeck to get the anchor ready or grab a mooring, and a furling code zero (a super easy to deploy light wind sail for cruisers) can be launched easily in front of the rolled up jib.
> 
> I read a little about Bernoulli and Reynolds numbers, but cannot remember any of it


There is no need to review Bernoulli, Reynolds or even Prandtl, etc. All you have to do is keenly observe that most frac rigs (compared on an equal/similar basis) _overwhelm_ masthead rigs when going to weather; and on the 'down side' the very same frac rigs will invariably use a spinnaker to beat the pants off a masthead (using a large LP genoa) 'going down'.

Such kind of strongly suggests that a masthead rig is only a compromise ... using the BIG jib/genoa instead of a 'proper' downwind sail and at the expense of 'pointing ability' for going uphill, to boot. It also suggests that the 'aerodynamics' of sailing more or increasingly 'optimize' with the fractional rig.
No 'iterated numbers' or 'theories' required, the 'ratings' databanks, the compilation of racing result over many many years seem to confirm this; all the while, the 'modern' (post ~1903) theories of aerodynamics help to explain 'why' that is.

All this stated, I still dont want an overly-tall rigid wing-sail on my crab-crusher 'Perryboat', thank you. But yet, I still fly a staysail 'under' a yankee topsail, as the speedo results show an increase of forward speed & VMG when pointing with this 'combo' .... and even that the staysail doesnt visibly _seem_ to be 'drawing' - thanks to modern theories of aerodynamics.

;-)


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## Liquorice (Nov 28, 2007)

Capt Vimes,
In support of RichH - you need to read the full article!


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## Spider0804 (Oct 12, 2011)

I would wonder why if the merits of fractional rigging are so beneficial to speed, why the fastest sailboat in the world uses a masthead overlapping jib.

One has got to think they have done more science models in a windtunnel than most other people.

http://hydroptere.com/news/508/146/...San_Francisco3-Copyright-Chrisophe_Launay.jpg

I think fractional shows benefits in racing classes but if we are talking about cruising I do not really think it matters too much where sail area is not restricted.


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## capt vimes (Dec 2, 2013)

first of all - the fastest sail"boat" is this one:








top speed over 500 m: 65.45 kts...
and secondly - i do not see hydroptere to be mast headed:









edit:
it is not even mast headed in your image... look closely again: the hounds are probably 9/10 of the mast - the tapered wingmast gives the look as being mast headed...


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## Spider0804 (Oct 12, 2011)

I just figured that thin bit at the top was an antenna or something, looks too small to be a mast.

I know they have many configurations and run a lower height fractional for ocean going though.


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## capt vimes (Dec 2, 2013)

well - in your image they were flying the jib and the main with the first reef...
in mine the main still with one reef and the smaller staysail, the jib furled away...


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## Spider0804 (Oct 12, 2011)

I am 95% sure that tiny bit on top is not part of the mast, but an antenna.

http://img.dailymail.co.uk/i/pix/2008/04_03/HydroptereLIV_468x225.jpg
http://4.bp.blogspot.com/_83C0d9qWNoU/TKTOwT6UZdI/AAAAAAAAYlg/INdqDNaPZJs/s1600/test.jpg
http://www.boatdesign.net/forums/at...70-15mph-peak-hydroptere-maxi-libryd-copy.jpg

Yea I am fairly certain it is masthead rigged.

In my picture the top of the jib goes all the way to the start of that spike.

Can not find any good pictures of just the top of the mast...

Anyway if it is fractional the stay is too high up to have the reason be mast bending and the jib goes higher than the mainsail or even with it depending how they run.

Is that not effectively the same as a masthead where the jib and main are the same height?

I was trying to make the point that if there was a benefit to doing it differently they would be doing it differently.


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## Stumble (Feb 2, 2012)

That isn't a jib, it's a code sail. And on your diagram above it is still running a fractional genniker. 

I would point out that hydroptere is so weird in its design and configuration I don't know e many iterations of sails it has. It is very possible that they have tried masthead rigs, fractional rigs, cat rigs, ect... The boat is a working test platform and doesn't really have a final configuration. You could probably find all sorts of weird combinations that have little to do with what the program thinks is fast. 

I think mastheads are fine, but they are a compromise. Beating upwind a fractional is always going to point higher and be faster. Reaching a asymetric is always going to be faster, downwind a spinnaker is always faster. The upside to a masthead jib however is that it does them all well on one sail. If you will never consider a furling genniker then a masthead is likely faster all round. But not on any one point of sail, it's more of an 'on average' rig.


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## Omatako (Sep 14, 2003)

Stumble said:


> I think mastheads are fine, but they are a compromise. Beating upwind a fractional is always going to point higher and be faster.


Yes you may be (and probably are) right but why? And please don't do like other posts and show me a picture of a boat that won a race and say "This is why". Geez 



Stumble said:


> Reaching a asymetric is always going to be faster, downwind a spinnaker is always faster. The upside to a masthead jib however is that it does them all well on one sail. If you will never consider a furling genniker then a masthead is likely faster all round. But not on any one point of sail, it's more of an 'on average' rig.


What reason is there to assume that a masthead rig will not use a code sail, gennaker or spinnaker off the wind? If a frac rig furls the headsail and a masthead furls the headsail and both fly similar downwind sails why would the frac be faster off the wind? Maybe a taller rig, maybe a bigger main, I'm not saying it isn't faster, all I'm trying to do is understand why.


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## bobperry (Apr 29, 2011)

Oma;
Boy, you are a snide little guy.

Time you educated yourself. All the info is out there. Lots has been presented here. We can't "make you" understand. It's not our lot to educate you. That's your job. You seem determined to stay in the dark when the light switch is right at hand.

Reach for the switch. Most of us did, years ago.


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## Stumble (Feb 2, 2012)

Oma,

Are you asking for mandates or realities? Fractional boats have a different rig system and sail profile than a masthead, it isn't just moving the forestay lower on the mast. There are a lot of things that change like main size, lead angles, J leingth, mast bend issues, aspect ratios. These things then change again as other things are decide like backstay vs running backs, shroud angles, ect. All of these things change and interact with each other thus it is very difficult to discuss one in isolation. 

Fractional rigs have the mast further forward, which allows for a larger main, along with a the smaller jib means that the sail area stays pretty close to the same. However it also results in a shorter J so you get a smaller spinnaker particularly on a symmetric which is limited typically by the J leingth. On the other hand an asymetric is less driven by the J length since the sprint pole makes up a significant portion of the foot leingth. 

A good example of how this works is the dimensions on the J-29 since there is both a MH and a FH boat designed to perform the same. 

The MH rig is 3.8' taller, .5' longer J, 1' shorter boom, ect...

The end result is the MH gives up 50 sq foot of mainsail, and gains 50 sq foot of jib sail area. But gains 150sq foot of downwind sail area because of the taller spinnaker. On the other hand if you were to put a MH kite on the FH the total sail area would be much higher downwind. 

It gets complicated because there are so many variables, which is why it is instructive to look at what the fastest boats are doing. Simply because they have the time and money to spend playing with the permutations. If you really want to learn why, you need to spend some time reading books on rig design and engineering. Because it is a complicated subject (and way past my expertise).


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## capt vimes (Dec 2, 2013)

another point might also be - but i could be wrong - that with new materials for the sails the main improved in performance a lot...
i see so many boats nowadays with fully battened mains from whatever-stuff-that-be and thus hugely increased performance when you compare it to the old white cloth hanging lousily from the mast...
the main is also easier and better to trim and thus there was a shift from small main, huge jib to huge main, small jib...









oh - and higher aspect ratio sails, i.e. smaller foresails with less J on a taller mast, just perform even better to windward...


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## Osprey 26 (Jun 28, 2013)

My guess is most of our wind measuring instruments, wind tunnel experiments show only one kind of wind. If there is only that kind of wind there would be nothing left behind so to speak.
Sir Isaac was probably right in explaining how things work.
Yes some sails do catch better then the other some of that extra unmeasured wind.
Faster then wind speed is result of this phenomenon on ice boats and such.
Probably to simple to be any good.


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## Shockwave (Feb 4, 2014)

Your numbers are a little off if the leech is 12% and the SMW is 1.8 on a J29. The mh downwind sail area is 667, the frac downwind sail area is 644. So a delta of 23 sq ft. Is this 23 sq ft enough to overcome the taller rig the frac j enjoys?

Upwind with blades the frac has an additional 3 sq ft, upwind with overlap the advantage goes to the mh rig (sorry, didn't bother to figure that delta) but again the frac has a taller rig and should be able to sail in more breeze and enjoy more shear.

But at the end of the day the mh is rated 6 seconds faster and is simply a better all around boat. My personal belief is the lower ce of the mh rig is a bigger advantage then initially thought. The mh boat stands up better.

Where is the frac an advantage? It's an easier boat to sail provided the extrusion/layup is strong enough to allow mh sails (codes through kites) and the spreaders are swept so runners and checks aren't required to keep the rig in the boat. Where is it a disadvantage? When more power is needed in the light stuff upwind a small j and I just doesn't give enough oomph with overlap. Hence the strong development of the mh codes and sprits. You can't simply add I because the geometry of the sail is structurally unfeasible, the aspect ratio doesn't work. So modern boats add j (sprit) and I (mast head sheave boxes) and essentially become a mh boat with a very big rig.

What's best? MH or frac? Looking at the J 29 the MH is best, looking at other boats, I don't know, there aren't many boats built as both MH and frac.



Stumble said:


> Oma,
> 
> Are you asking for mandates or realities? Fractional boats have a different rig system and sail profile than a masthead, it isn't just moving the forestay lower on the mast. There are a lot of things that change like main size, lead angles, J leingth, mast bend issues, aspect ratios. These things then change again as other things are decide like backstay vs running backs, shroud angles, ect. All of these things change and interact with each other thus it is very difficult to discuss one in isolation.
> 
> ...


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## MedSailor (Mar 30, 2008)

bobperry said:


> Oma;
> Boy, you are a snide little guy.
> 
> Time you educated yourself. All the info is out there. Lots has been presented here. We can't "make you" understand. It's not our lot to educate you. That's your job. You seem determined to stay in the dark when the light switch is right at hand.
> ...


Bob, you're not really going to go after someone else for their snide or grouchy posting tone are you? 

As for your lot not being to educate us, I kind of hoped that you would make it your lot since you're one of the few high experts on the subject. With my opening post I posted a lot of BS about rigs, because when I DO try and educate myself, that's what I get back. A lot of dock-talk and eyebrow raising BS. I'm amazed at the sources sometimes too. A racer with a wall of prestigious trophies once told me that only real advantage of a fully battened main is "extra sail area." Really? I have a hunch there's more to it than that...

So, if not you, then can you help us find the right switch? Any good book recommendations? Good websites or Videos? Right now I am finding much more chaff than grain on this particular subject.

MedSailor


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## bobperry (Apr 29, 2011)

Med:
I just can't do it. It would take a book to carefully go over all the varaiables here. I think it's a mistake to divide the the subject into two groups, i.e. masthead and fractional. There are so many sub-groups involved and that's without even mentioning hull shapoe differences in older masthead boats and movdern frac boats. I don't have the time to do it justice. Not sure I really know enough either.

I think there has been a lot of good material presented here and yes it has been clutterred with some less than accurate comments. But that's life and par.

With modern sail fabrics the entire picture has changed. The masthead rig of the old racer with its in line shrouds ansd super bendy stick was perfect with dacron sails as the rig could be shaped to change the draft characteristics of the sail relative to the conditions. With new, high tech sails, the shape you want is sown in from the start. You cannot stretch the sail to change the draft. If you need a fuller jib you can play with halyard tension and sheet lead but if you are seriously racing you'll put up a fuller jib. The LP may be the exact same as the flatter jib but the draft will be deeper. With the main you have halyard cunningham and outhaul to play with but with spreaders swept as much in some cases as 30 degrees you are not going to bend that "tripod" rig.

But if you go back 15 years you still had frac rigs that were effective but in those days mast bend was used and shrouds were in loine or almost in line. That's an entirely different situation.

Probably the biggest single factor to the success of the frac rig is we have come to learn that masive genoa overlap is not nearly as efective as additional luff length. Today it's all about leading edge.

Years ago the first of the Aphrodite 101's came to Seattle. About ten of theswe were ordered in Seattle. They came with a standard 100% jib. The class felt the boat would be underpowered in the light Seattle breezes. An overlapping genoa was built and two boats, one with 100% and one with genoa went out for two full days of testing in light air. The result was the 100% jib was just as fast as the boat with the genoa.

With squatty old CCA proportion rigs overlap was seen as a way to increase the SA/D. With the new frac rig the SA/D is much higher to begin with so there is little to gain from relatively inefficient overlap. Pragmatic advantage being you no longer need an "inventory" of genoas. I sail my frac rigged boat for 15 years with two jibs.

In summary (I hope) pretty much everything has changed. The question masthead or frac is multi dimensional and not just two dimensional geometry.

Racing FRANCIS last weekend we had a jib hal lead block failure resulting in a long beat in up to 30 knots AWS with an ugly looking, baggy jib. I was driving. We did the best we could with the jib and I tried to sail the boat mainly on the mainsail, our big sail, our driving sail. We did exceptionally well, walking away from the fleet upwind despite out jib hal handicap. This would not have happened with a masthead rig. Wewould have been crippled.

Sorry about being snotty. It's my vile nature.


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## christian.hess (Sep 18, 2013)

awesome info


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## bobperry (Apr 29, 2011)

Thanks muchly Christian. I'm jammed today or I would have taken more time. Off to San Francisco tomorrow to give a talk at Saint Francis YC where I will have to act like an "expert". Getting ready today. Also doing my SAILING reviews today where I will once again have to convince myself that I am an "expert". No always easy to do. I'm still learning like everyone else.


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## christian.hess (Sep 18, 2013)

man! cool to talk to you at least here

my experience with frac rigs is limited to dinghies and folkboats and hobies and the like and my limited experience tells me that frac rigs like to sail by the main and respond better to the main than a masthead rig, they also sail more like dinghies...

case in point my islander has a very small aspect main, bendy stubby mast with inline spreaders and will sail slow if using anything less than a 130 genoa...big overlap etc...

I have noticed that many 70s boats were all about the size of the jib with little importance given to the main

contessa 32, islanders,yankee 38, almost any ior boat of that era

in any case today Im completely lost in all the variations as Im always stuck boat wise 30,40 years back unless were talking dinghies...

anywhoo back to rigs


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## Stumble (Feb 2, 2012)

Shockwave said:


> Your numbers are a little off if the leech is 12% and the SMW is 1.8 on a J29. The mh downwind sail area is 667, the frac downwind sail area is 644. So a delta of 23 sq ft. Is this 23 sq ft enough to overcome the taller rig the frac j enjoys?
> 
> Upwind with blades the frac has an additional 3 sq ft, upwind with overlap the advantage goes to the mh rig (sorry, didn't bother to figure that delta) but again the frac has a taller rig and should be able to sail in more breeze and enjoy more shear.
> 
> ...


Shockwave,

The rates size for the J-29 spinnaker is 630sq feet (FH), 751 (MH) for a delta of 121sq feet. It's a pretty major upsizing relative to the boat. If you put a MH kite on the FH boat however the downwind sail area advantage would flip back to the FH.

My numbers indicate the FH is typically rates 3sec/mile slower than the MH, which in my eyes is directly relates to the size of the spinnaker. But I haven't had a chance to see the two boats side by side.


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## MedSailor (Mar 30, 2008)

Thanks Bob for the info. Don't worry about the San Fran talk, you're an expert compared to the audience, and that's why they're in their seats and you're up front. 

I get what you mean about "convincing yourself that you are an expert." I would consider myself some kind of expert on a few things, but only because I've come to realize that there is no such absolute thing as an expert. Some just know more than others in certain areas of knowledge. It's part of why I added the qualifier "high expert". It's kind of like the term "smart", as in, "he's really smart". I find it such a useless and generic word. Show me a "smart person" and within 5 minutes I bet we can find a topic on which they know virtually nothing. I have a buddy who is a rocket scientist (really, he is) and he can be just as "dumb" as the rest of us mortals from time to time. 

Thank you for your rig primer. It has really helped me sort my question into many more sub-questions that will help me go forward. It also helps me understand why there are so many, seemingly conflicting opinions on the subject. Since rig evolution is a moving target, some info (from an "expert") may have once been good info, but is now outdated. Some info comes from big budget racing, small budget racing, or cruising perspectives. 

I can also see that sorting out gains vs trade-offs for an individual gets complicated very quickly. Upwind gains are often race winning gains, but perhaps not for a cruiser. Also, your point about having different cuts of 100% jibs demonstrates the different requirements people have for their rig design and performance. 

For me though it's all academic. I have a very limited list of boats I can choose from that fulfill all of the compromises that myself and my wife can live with. For now, they're all older masthead rigs. Still, I love learning and sailing is still my favorite subject to continue that learning. 

MedSailor


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## Shockwave (Feb 4, 2014)

Your right, I transposed a number. The times I've raced on the 29 mh it seemed quicker all around then the frac, it's been a few years though... Not sure if it was the boat, the sails or the sailors.



Stumble said:


> Shockwave,
> 
> The rates size for the J-29 spinnaker is 630sq feet (FH), 751 (MH) for a delta of 121sq feet. It's a pretty major upsizing relative to the boat. If you put a MH kite on the FH boat however the downwind sail area advantage would flip back to the FH.
> 
> My numbers indicate the FH is typically rates 3sec/mile slower than the MH, which in my eyes is directly relates to the size of the spinnaker. But I haven't had a chance to see the two boats side by side.


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## Stumble (Feb 2, 2012)

Shockwave said:


> Your right, I transposed a number. The times I've raced on the 29 mh it seemed quicker all around then the frac, it's been a few years though... Not sure if it was the boat, the sails or the sailors.


No worries... And it yet again proves the difficulties in these conversations. I could take either a MH or a FH load it with the right sailors and smoke the other one doesn't matter which. Because the boats really were designed to the same performance ( J boats intended the two to race OD with each other) it is fun to look at how they played with the numbers to try and get that result. What's equally interesting is what people would do today... Larger higher aspect mains, asymmetric chutes, Code zero's (which really change the whole game), MH spins on fractional jibs.

Oh so many fun games to play.

What I think needs to be carefully reserved is that just because a FH may be better on a windward leeward race course may have little do to with how it works out on a cruising boat. The harder you are willing to work the boat and sail inventory the better a fractional looks. If you are just going to fly white sails then a MH starts to average out better.


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## hellosailor (Apr 11, 2006)

bob, if you won the race in a crippled boat, that doesn't reflect anything on the rig type. It just means someone designed and built a fast boat. Or, it was "take your kids to the races" day on the other boats. Or, if she also won on corrected time, Francis isn't rated correctly.(G)

So far I've seen no one post anything objective. An AC boat might have the wing (a real wing, not a sail) end two meters down from the masthead simply because more sail that high would only help it capsize faster--a real issue for them. Or, it might have been too tall to transport at that point. Just looking at it, without knowing the facts, is meaningless speculation.

Similarly, all the comparison of masthead to fractional rigged vessels ignore the larger questions of whether the "faster" rig is being compared apples-to-apples to the entire boat design having the same balance (fore and aft) and same sail area (main and fore and aloft) and without those things being apples-to-apples, all we have is what a dog knows about elevators.

Huh? 

Yeah, I get up in the morning, and my master puts us in a box, and then he opens the door, and the whole universe is changed! And then we get back in, and he opens the door again, and the whole universe is changed back! I don't know how he does it, he's obviously God.

Well...that's how the dog sees it. Motors, cables, switches, Otis brakes...the dog knows nothing about those, he only thinks his master is remaking the universe.

From what I've seen, the question of rig type comes down to "This is what the boat comes with. This is what the grumpy old man, ergh, distinguished marine architect (G), says makes this boat work, and I'm not gonna argue with him."

Funny thing is, there's someone designing both kinds of rigs, somewhere, sometimes, isn't there?

Argue with the designer, and he'll give you a yawl like the Pearson 424. You know, where the yawl boom keeps trying to take off the helmsmen's head?


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## bobperry (Apr 29, 2011)

Hello:
I'd respond but I'd need a translation first.

I am currently working on:
One frac rig
One ketch rig
One masthead sloop that just became a frac rig.


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## MedSailor (Mar 30, 2008)

bobperry said:


> Hello:
> I'd respond but I'd need a translation first.
> 
> I am currently working on:
> ...


Ahhh... but is the ketch fractional?  Can I have a mashead main on my ketch with a fractional mizzen please? I think that would be the perfect rig.

Medsailor


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## bobperry (Apr 29, 2011)

Frac mizzen? No sure how to do that.
Yes my ketch is a masthead design because I have a bridge clearance issue to deal with.


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## lancelot9898 (Dec 30, 2008)

Very interesting discussion. There are many variables that come into play when making such a comparison that to me saying a fractional rig is better that a MH rig has little meaning. Fluid dynamics was not my favorite subject in college since much if not all is based on emperical data whereas I always needed to go back to basic theory to understand what was being observed. Thank you Mr. Newton. I should spend some time reading Gentry's articles as RichH suggests, but doubt if I could grasp the information. Look at some of the improvements and innovations in aerodynamics over the past decade. Large commercial planes (and even smaller ones) now have a vertical component on their wing tips to enhance performance. The AC series boats have a main with the head no longer pointed but now it has a long horizonal component. The stealth fighter with all its odd shapes was thought it would not fly efficiently, but yet it does.

As time goes on other improvements to get better performance out of fluid dynamics will take place and I'm sure that some will seem contrary to present day understanding. My 2 cents.


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## Shockwave (Feb 4, 2014)

I think the future will bring us back to full on mh rigs, giving up I is giving up power, with a row of window shades. Pick the power you need, be it a frac or mh, upwind or downwind. The open 60's have moved the butt back to allow enough j for mh upwind headsails tacked to the deck, not the sprit.




























New cruising boats are following with multiple headsail options, Tartan being one. But I'm curious how many cruisers really want to work that hard?



Stumble said:


> No worries... And it yet again proves the difficulties in these conversations. I could take either a MH or a FH load it with the right sailors and smoke the other one doesn't matter which. Because the boats really were designed to the same performance ( J boats intended the two to race OD with each other) it is fun to look at how they played with the numbers to try and get that result. What's equally interesting is what people would do today... Larger higher aspect mains, asymmetric chutes, Code zero's (which really change the whole game), MH spins on fractional jibs.
> 
> Oh so many fun games to play.
> 
> What I think needs to be carefully reserved is that just because a FH may be better on a windward leeward race course may have little do to with how it works out on a cruising boat. The harder you are willing to work the boat and sail inventory the better a fractional looks. If you are just going to fly white sails then a MH starts to average out better.


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## outbound (Dec 3, 2012)

Whew- I'm still at the stage of learning how to sail my boat efficiently. But appreciate these posts as inspite of myself did learn something. My impression has been for dilettantes like me it's easier to get close to best trim with a MH than a frac. ? Am I fooling myself in thinking the MH is more forgiving? We have non stretchy, crawly sails. We fool with halyard,out haul, and back stay.


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## Stumble (Feb 2, 2012)

Shockwave, 

I am not sure what IMOCA rules are on sails and rigging so I am not sure how that drives their sail selection. They also have permanent reaching struts which make large jib better in more conditions since they can be trimmed properly. 


Outbound, 

I don't think the rig matters much in terms of trimming, it is just different. The size of the jib matters more. So a FH 155% vs a MH 155% is pretty much the same trimming the sail (trimming the rig is very different). But a lot of FH don't carry large overlapping jibs, they use a massive main and just a small blade for a jib. Just enough really to balance the boat.

My trimaran for instance can barely sail under main alone because the main is so powerful it will drive the boat head to wind no matter what you do. A little bit of jib even if it's trimmed badly solves this.


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## outbound (Dec 3, 2012)

Have solent rig. Once over~10-15K AWS find boat does just as well with solent as with genny except downwind. I guess a demonstration of the lack of effect from overlap. Then downwind find better to use genny on a pole up to ~20-25K AWS even if means a reef in main. 
Use a parasail so the comments about spinnakers/code zeros etc. don't apply. Think for cruisers the old saw "gentlemen don't go to weather" applies. Think it's much harder to get to your polar predictions in light/moderate air then heavy. Think swept back spreaders and running backstays make for a more complicated rig. Don't put the main on the spreaders downwind so think I would give up some with swept back spreaders. Understand the fractional rig makes more sense in theory and for racers but for the type of sailing I do and intend to do like being just under 64'. Like only needing to rig the running backstays when weather demands and when I deploy the removable stay for the stormjib. Like that my rig doesn't pump. Like not having jackstays to maintain. 
Still as Bob says current generation of sails don't stretch and masts with swept back spreaders don't bend much so a lot of what I was taught to do no longer applies. Always learning. Thanks. Boat got 2 new coats on her bottom. At my level of sail trimming that will probably make more difference than anything.


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## outbound (Dec 3, 2012)

Thought one of the big pluses of frac rigged boats was you got a lot more out of adjusting the backstay beyond increasing fore stay tension. ?Is this still true?


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## Stumble (Feb 2, 2012)

outbound said:


> Thought one of the big pluses of frac rigged boats was you got a lot more out of adjusting the backstay beyond increasing fore stay tension. ?Is this still true?


It depends on the boat and the rig. Generally the backstay is just to play the top of the main, and it leaves the jib tension alone. But then you have a lot of fractional rigs without backstays with just runners, or some that don't worry about anything but prebend.

This is where rig design gets really fun. Since you can design a boat without needing to absorb all the backstay tension you can design a different hull. The J-35 for instance sailed best upwind with about 3500psi of backstay pressure. But the boat wasn't designed to take this much pressure and the hull would start to flex. On the fastest boats reinforcing the hull became necessary to offset the mast pressure.


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## Osprey 26 (Jun 28, 2013)

lancelot9898 said:


> Very interesting discussion. There are many variables that come into play when making such a comparison that to me saying a fractional rig is better that a MH rig has little meaning. Fluid dynamics was not my favorite subject in college since much if not all is based on emperical data whereas I always needed to go back to basic theory to understand what was being observed. Thank you Mr. Newton. I should spend some time reading Gentry's articles as RichH suggests, but doubt if I could grasp the information. Look at some of the improvements and innovations in aerodynamics over the past decade. Large commercial planes (and even smaller ones) now have a vertical component on their wing tips to enhance performance. The AC series boats have a main with the head no longer pointed but now it has a long horizonal component. The stealth fighter with all its odd shapes was thought it would not fly efficiently, but yet it does.
> 
> As time goes on other improvements to get better performance out of fluid dynamics will take place and I'm sure that some will seem contrary to present day understanding. My 2 cents.


Oh, I really like that how is explained. Also like how dedicated professionals, and experienced individuals in general help us understand what going on with sails, wind power.
There is also lot to learn, and if questions from us not in same class so to speak probably can help.

In lab type wind tunnel tests we do get basic knowledge. In real world it isn't that simple to get 100% same results all the time. 
Wind instruments have some inertia and show more stable wind speed.
My guess is there are all kind of speeds in that spectrum like in white light.
Ice Sailboats with little resistance use those micro speed bursts to go
3-5 times faster then indicated wind speed.


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## tommays (Sep 9, 2008)

This is interesting due to the long term Success of J29s in this area right up to NOW 

It is more so because despite all the variation's the MH/outboard is the most popular and sought after model in this area


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## Stumble (Feb 2, 2012)

So I was doing some reading last night and this conversation popped into my head. Go take a look at the current generation of C class catamarans. These race in a pure development class, and the only restriction on sails is maximum sail area. Right now they are all using high aspect wing cat rigs. There isn't even a jib to be seen. And some of these teams have massive amounts of money to throw at the problem since the. C cats are test beds for large boat programs (Americas Cup, IMOCA, maxi cats, ect).


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## Shockwave (Feb 4, 2014)

Flex? The backstay? Or the over anxious guy on the checks trying to drive the spar through the bottom of the boat? 

I like in line rigs, even with their short comings, versus swept spreader rigs. In line rigs have a larger range of movement allowing better draft depth control but for a cruiser a swept spreader rig is probably better.



Stumble said:


> It depends on the boat and the rig. Generally the backstay is just to play the top of the main, and it leaves the jib tension alone. But then you have a lot of fractional rigs without backstays with just runners, or some that don't worry about anything but prebend.
> 
> This is where rig design gets really fun. Since you can design a boat without needing to absorb all the backstay tension you can design a different hull. The J-35 for instance sailed best upwind with about 3500psi of backstay pressure. But the boat wasn't designed to take this much pressure and the hull would start to flex. On the fastest boats reinforcing the hull became necessary to offset the mast pressure.


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## Stumble (Feb 2, 2012)

Shockwave,

On the J-35 I raced on we carried so much backstay pressure (on top of 16" of prebend) that the hull would actually flex. Based on our measurements the boat shortened by about 2" and widened by 4" (I think, I don't remember the exact measurements anymore). To counteract this we rigged in internal wire support system that tensioned the whole boat to prevent it from flexing. 

This is an extreme example of how to get enough forestay tension on a MH can cause all sorts of weird spiraling issues.


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## GeorgeB (Dec 30, 2004)

Backstay tension until the boat bends is pretty standard SOP. To calibrate the Cal 40, we stretched a line between the pulpit and pushpit. Marked the intersection with the mast and applied tension until the line "sagged". 2,000# is our "beating - heavy air" setting and our max setting is 2,500#. We also completely slacken off the back stay for downwind work.


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