# Deck Stepped Mast or Keel Steeped Mast???



## tbeargladd (Mar 23, 2006)

Good day to the sailing world!

It's been some time since I've requested any other opinons, I've have a great delima an asking help with information on this subject. This is regarding a Deck Stepped Mask, or a Keel Stepped Mask. Should a Keel Stepped Mask give you far more strength than a Deck Stepped Mast? 

Does a Keel stepped Mask add more overall weight to ones boat? 

Wouldn't one want to consider a Keel Stepped Mask than a Deck Stepped Mast and why? 

I've check out a lot of Deck Stepped Mast Boats, that are very strong and good sailing boats, why would I want a protenial hazard? Or is this not such a harzard!

Thanks for you help! 
Ted Gladden


----------



## mike dryver (May 13, 2006)

tbeargladd there are two schools of thought on this sub. a deck stepped mast reduces the holes in the hull/ cabin top by one. so if you get rolled there is one less potential leak/ water ingress while rolled. however more than likely you will loose the stick, which will make a jury rig extremely difficult. also there is a compressin post in side where the mast would be which is normal, but the design must be such that it will adiquately support the mast rigging and sail loads.
with a keel stepped mast there is the hole but if properly secured will leak but not alarmingly. also if rolled usually the mast will break at the spreaders if at all leaving a stump to get you home so i've read about. neither is a good senario as both can hole the hull until you clear the debris/ mast and rigging and let it sink


----------



## paulk (Jun 2, 2000)

You'd really need an engineering report to find out how strong any mast setup is. Star masts are stepped through the deck, and they break all the time. Moody masts are often deck-stepped, but don't seem to fail much. some long-haul sailors like keel stepped masts because the partners may provide some support if a shroud or stay parts, and keep the spar up long enough to take the load off it. Racers may think a longer keel-stepped mast provides more leverage for bending it. Others like deck-stepped masts so they don't interfere with interior arrangements, or provide a conduit for rain to hit the mast and end up in the bilge. Both setups seem to work. It's a question of what works for you.


----------



## tbeargladd (Mar 23, 2006)

*Keel or Deck*

First of all good day, to all replier's and hopefully more collaboraters.

What a great amount of opposition here. I love it! Some very interesting facts above for me to consider and hopefully helps to assist any and everyone else who finds this a useful subject. More question below!

If a keel stepped mast corrodes at the keel how would a survery be able to diaganose if their is structural problems with the mast and keel?

Is their a life expectancy of a mast before it would need to be replaced and if so what is the expectancy? Like the standing rigging, suppose to be good for up to ten years! True/False?

If a deck stepped mast doesn't have a compression post and the mast has concave the cabin top, would that area on the cabin top have to be cut out and replaced or would the entire cabin top have to be replace or some type of support would be just enough to give the sunken portion of cabin top some lift to its normal stature?

When I see a "rubber boot" (I hope that is the correct terminology) at the bottom of the mast is that what protects the Keel Stepped Mast from leaks into the interior or does this assist the Deck Stepped Mast from water softining the cabin top?

As many boats as their are that are Deck Stepped the amount over shadows the amout that are Keel Stepped, other words I see more Deck stepped than I have seen Keel Stepped. Does that have any affect of the value of the boat?

Thanks everyone for your words of wisdom is truely appreciated.

Ted Gladden


----------



## sailandoar (Mar 20, 2006)

*Boat Design Forum => Similar thread ...*

http://boatdesign.net/forums/showthread.php?t=10203


----------



## sailingdog (Mar 19, 2006)

Both types of masts have pros and cons. A properly designed deck-stepped mast is preferable IMHO. There are too many possible problems with having the mast go through the cabintop, such as delamination of the cabintop, water leaks, etc. 

Also, a properly designed deck-stepped mast can often be designed to be unstepped without a crane. This is very useful for boats that are travelling in areas without full marine service facilities.


----------



## Jeff_H (Feb 26, 2000)

This is from a draft of an earlier article that I had written for a different venue:

"I personally strongly prefer a properly designed deck-stepped mast over a keel stepped mast but once again this is an area where opinions can differ widely. There is no right answer here. There is a contingent that thinks that the only proper way to step a mast is on the keel. There is a very respectible logic to that position but it is a logic that can be engineered around and which comes out of a historical context that is less relevant with more modern designs and materials. 

To start with the basics, the base of a mast has a vertical and horizontal thrust to it that tries to push the base of the mast downward through the bottom of the boat and also sideward off of the mast step. In normal conditions the down load is several times greater than the side load. Beyond the loads imparted to the boat, there is also the issue of the loads that happen internally within a mast. When you look at the structure of a mast it is really a truss standing on end, although it does not completely act as truss because the components of a truss are not supposed to have bending loads on them and the individual panels of the mast are exposed to bending as well as axial loadings. Ideally the loads in the mast are primarily axial (acting along the length of the mast) rather than in bending (acting perpendicular to the long axis of the mast). Of course masts do have fairly large bending loads imparted into them. The two most often cited reasons for keel stepped masts being considered stronger is the way that the bending loads (moments) are distributed within the mast itself and the way that the mast imparts its loads into the boat. 

If the goal of designing a mast is to reduce bending moments within a mast, the greater the number of panels (segments between shrouds and other supports) the smaller the moments tend to be. In the days when single spreader rigs were most common a keel-stepped mast added one extra panel, the segment between the mast partners at the deck and the keel. This has become less significant as bigger boats which have routinely gone to multiple spreader rigs and moment connections at the deck mounted mast steps. 


In terms of the way that the mast imparts its loads into the boat, masts are generally located in the area of the cabin trunk and because of the shape of the cabin (i.e. the deck folds up at the cabin side and horizontal again at the coach roof) this area, if not engineered for side loads is more prone to lateral flexing than would be the keel. One idea behind a keel-stepped mast being stronger is that with a keel stepped the mast is not supposed loads are put loads into the deck. 

In reality, this ideal is rarely accomplished for a number of reasons. First of all, if the mast is not tied to the deck or the deck tied to the keel near the mast, either with a tie rod or a tie from the mast to the deck and a connection from the mast to the keel, the downward force of the mast working in opposition to the upward loads of the shrouds can pull the hull together like a bow and arrow lifting the deck and separating the joint between bulkheads and the deck. You sometimes see this type of separated bulkheads on inexpensive or early fiberglass boats with keel stepped masts. 

Not only do keel stepped masts impart vertical loads into the deck (through the ties mentioned above) but they also typically end up imparting side loads as well (if they are going to reduce the moments in the mast as mentioned above). This somewhat reduces the structural advantages of a keel-stepped mast to next to zero assuming that a deck-stepped mast is properly engineered, and that is a big if!

There are several things that I consider critical to engineering a deck stepped mast properly. Primary is having a jack post below the mast. A jack post is a vertical member that carries the vertical loads of the mast to the keel. My preference is to have an aluminum jack post rather than a wooden one but a wooden post can work as well. The other issue is the distribution of the side loads. Ideally there should be a bulkhead or ring frame adjacent to the mast that can take the side loads and distribute them into the hull. These are obviously more complex to do than simply having a fat spot on the keel for the mast step to land on. 


My objections are to the purely practical. Keel stepped masts mean that there is always water in the bilge. This water comes in at halyard boxes and other openings in the mast and nothing you can do will stop that. Second, it is way harder to step and unstep a keel-stepped mast making the boat more subject to damage in the process. Beyond that if you loose a mast (I have lost two in my life) it is better in my opinion to loose a deck stepped mast because a keel-stepped mast is more likely to damage the deck when it fails and a deck-stepped mast is easier to clear away. The keel stepped mast advocates point out that you are more likely to end up with a bigger stump after the mast fails. I am not sure that that is the case if you are able to tow the rig as a drougue until things quiet down enough to rig a jurry rig. I am not sure what you do when the boat is being beaten to death by the upper portion of a mast that has buckled 20 feet off the deck at the spreaders. . 

My preferred set up is a deck stepped mast that has a welded flange on its bottom that is through bolted through the deck into the top flange of a structural aluminum jack post. My new boat has a keel stepped mast. It is my intent to pull this mast and have it modified to that arrangement if I ever go offshore with her."

Jeff


----------



## TSOJOURNER (Dec 16, 1999)

*Keel steped masts*

Just my two cents, I just bought a 37 foot O Day sailboat without a survey and on taking it out on my maiden voyage, I lost the fore stay due to improperly installed swage fittings and a cracked deck fitting. Because the mast is keel steped nothing happened and I was able to spill wind enough to get to the boat yard 20 miles away. Had the mast been deck stepped I believe it would have come down on top of us. Just my opinion.


----------



## Jeff_H (Feb 26, 2000)

If there had been a moment connection at the mast step, or a forward lower shoud, you would have had an equal chance of keeping your mast whether the mast was keel or deck stepped. But with a normal compression deck stepped mast and no forward lowers you are right that your circumstance would have been a lot more perrilous. 

Jeff


----------



## tbeargladd (Mar 23, 2006)

Thanks to everyone, that was vital information very in dept and helpful! Their is still a choice to be made. This will take some time to figure out Thank's again for all your support!

tbeargladd


----------



## sailingdog (Mar 19, 2006)

Jeff H- 

Wonderful reasoning, and much in line with my own. My current boat has a deck stepped mast, and the lower shrouds should work quite well to support the mast in the case of a failure as they are 1.75" stainless struts, not wire...and take both compression and tension loads. 

The compression post inside the cabin is not aluminum, but stainless steel, which is far stronger and more fatigue resistant IIRC.


----------



## TSOJOURNER (Dec 16, 1999)

I have a j/24 with a keel stepped mast. It's quite difficult to step without a crane. It's 37' long, and drops thru the deck about 4'. My buddy lost his mast on a j/24 recently, but it broke in 1/2 and he was able to stow the upper 1/2 and no one was injured. (the mast stays together because of all the halyards). I do get water in my bilge after a rain storm, but not enough to be a bother. I noticed the j/22 (a newer design) now has a deck stepped mast. I guess either is fine if it's done well. There is a beneteau for sail in the classifieds here that has a deck stepped mast but the stringer below it is broken, or bent down 3/4 inch and they've been quoted $10k for repairs.
Plus


----------



## LaLeLu (Mar 17, 2006)

Let me guess - you advocates of deck stepped masts own boats that are deck stepped? Everyone here with a boat is going to give you an answer that is consistent with the boat they own. My mast is keel stepped. We intentionally purchased a boat with a keel stepped mast. IMO, Cruising boats are much more likely to suffer mast failure from failed standing rigging. If a keel step mast has a rigging failure, you are much more likely to be able to save and jury rig than with deck stepped. I know of a keel stepped boat that had a collision that tore off all its standing rigging. The mast still stayed up. My mast has a huge gaping hole in it anyway (ie roller furled), so definately I want to keep it out of the water


----------



## hellosailor (Apr 11, 2006)

Tbear you don't mention what size boat you are looking for or what purpose.

I have to say that my first preference is for keel stepped in the belief of "KISS", "keep things simple stupid!". One spar, no deck fitting for it, no compresion posts or compression scheme, just seems like less chance for bad engineering or extra weight or other problems. I mean, SOMEthing has to carry the load down to the keel anyway, why not the mast itself?

But I readily concede that on small boats (<30') with a deck-stepped mast, it sure is nice to know there's no water coming in at the mast partners or from condensation in the mast. No water is a good thing.<G>

There are other reasons, on racing boats like the J/24. You couldn't build a J/24 with a deck-stepped mast, because deck-stepped always means the mast sits on a fixed base plate. On racing boats you want to be able to MOVE the base of the mast fore and aft, so you can adjust the rake (amount of tilt) and yes, that's part of racing trim. But for cruisers? it just isn't done, or needed.

Odds are that whatever you are looking at, if it was engineered carefully, and maintained properly (big issue in used boats) it will be suitable for inshore and coastal sailing regardless of how the mast is stepped. Both can have problems, and if you are looking for a bullet-proof boat...there are bigger issues than the mast.


----------



## Valiente (Jun 16, 2006)

I currently own a keel-steeped racer-cruiser. I do get water in the forward sump after heavy rains, but that's a sponge and bucket five-minute job. While I am confident in my keel-step, I am aware that the step itself must be maintained. Mine has a touch of rot and will need cutting out eventually and a redo...big job. Also, the mast itself is pretty old school and blocks the passage forward. Ignore this job and you can have a situation where the mast can pound a hole through the keel. This happened with a poorly maintained C&C at my club. 

All that said, I do like the solidity and simplicity of the "big stick" and I wouldn't change my current boat.

By contrast, the boat I am considering buying next for world cruising is deck-stepped and pivots on a massive tabernacle. The stays are many and sized "x-large" for offshore, and the compression posts below are two in number and are aluminum, allowing a two foot gap between them, almost like a doorway into the dining area, not to mention an excellent place to hold on in a seaway. 

The advantages of a deck-stepped for the long-distance cruiser are considerable in terms of maintenance, shipping the mast for canals/low bridges (think of getting up rivers to hurricane holes in storm season) and maintenance/inspection, and in terms of lessening the need to go aloft...although this need is never gone entirely. 

Finally, it does keep the deck watertight, or more so than keel stepped. In a breaking sea, this could be quite important.

It does depend on the build quality of the boat (this one I've described is a tank) and the intended use.


----------



## Jeff_H (Feb 26, 2000)

_" Let me guess - you advocates of deck stepped masts own boats that are deck stepped? Everyone here with a boat is going to give you an answer that is consistent with the boat they own. "........ LaLeLu_

Actually, I own a boat with a keel stepped mast, but I feel so strongly about having a deck stepped mast that I plan to convert my keel stepped mast to a Deck stepped mast with a moment connection at the deck before doing long distance offshore passages with my boat.

As I explained in other discussions, with a full moment connection at the deck, you are no more likely to loose the mast than you would with a keel stepped mast, you are equalliy likely to have a stub standing, but you have a way of jetisoning the mast before it holes the hull in heavy going.

Jeff


----------



## Curt (May 29, 2006)

I have noticed some of the Hans Christians have a deck-stepped mast with a keel support pipe. I had thought the deck-stepped design would have been a shortcut but now that I am looking into many other boats I see these are not builders that are characteristic of taking shortcuts. 
It would be interesting to know how many of the top five companies for quality go with the deck stepped mast.


----------



## sailingdog (Mar 19, 2006)

Deck-stepped masts are often heavier than comparable height keel-stepped masts, as the keel-stepped masts are supported a fair amount by the mast partner, where it passes through the deck.

Many good bluewater boats have a deck-stepped mast, including Cheoy Lee designs, the Hunter 426, Dufours, Hans Christians, Nimbles, Catalinas, Hallberg-Rassys, Malos, Sadlers, Albin Vegas, Cape Dorys, various Cals, Columbia 26s, Jeanneaus, etc...

Many of the boats listed are proven, capable blue-water boats. There are also many not-so-capable boats that are designed with deck-stepped masts, and there are many bluewater proven boats with keel-stepped masts.

I think a lot of what makes a deck-stepped mast preferable to a keel-stepped mast is personal preference. I prefer a deck-stepped mast, as they can be much easier to work with, especially in remote locations, where the equipment to deal with keel-stepped mast is not available.


----------



## Valiente (Jun 16, 2006)

sailingdog said:


> I think a lot of what makes a deck-stepped mast preferable to a keel-stepped mast is personal preference. I prefer a deck-stepped mast, as they can be much easier to work with, especially in remote locations, where the equipment to deal with keel-stepped mast is not available.


This is why I favour deck-stepped over keel-stepped: ease of access, repair and occasionally transport. Given a strong, well-founded boat, and the ability to work with, and not against, heavy weather, the mast isn't going to be a worry anyway. If we ever do get rolled, I want to have as few holes on deck as possible.


----------



## TSOJOURNER (Dec 16, 1999)

I didn't read in detail all the posts. However, I own both a deck stepped 35' sailboat and a keel stepped Pearson 10M. I have read in the past where there is on the order of a 10 to 15% loss in column strength deck vs. keel stepped. That said, a keel stepped that jumps its shoe in the bilge can quickly hole a hull. Either one lying alongside after failing can hole the hull. I know of two deck stepped failures - not the step, but rigging failure - that each owner felt was preferable to a similar keel stepped failure. One was due to quick retrieval, the other was in 10' short, steep seas off Culebra. If the rigging failed and the mast jumped its shoe in the Culebra incident, it would've been messy below decks. Instead, the mast went over and had to be cut loose in 80' of water to avoid further hull damage. Like was said earlier, it's a preference thing, each having its own nuances but if properly engineered and constructed the deck stepped is fine. Mine isn't attached at the deck shoe, but ideally should be on a tabernacle and through-bolted.


----------



## sailingdog (Mar 19, 2006)

The deck stepped mast on my boat has two fairly hefty stainless steel a-frames that will help to keep the mast in position, even in a rigging failure. If the mast were to fail, it would probably do so above the larger a-frame, which is designed to act as lower shrouds.


----------



## tbeargladd (Mar 23, 2006)

*Reply to all on this thread*

Good day, all responses

Thanks for the advice, it seems this is a big controversial subject. This advice has been helpful. The passage I plan to take is long distance, possible a circumnavigation.

True most of the blue water boats I have look into does have a deck stepped mast. Which is why I was so curious why such a preference would be on a Keel Stepped Mast for ocean crossing. Did this come about because of the Fastnet Race or has a keel stepped mas always been more consider for ocean crossing sail boats.

This is a decision that is as bad to decide a fin keel to a long/full keel which may take a while to figure out which way to go or what kind of sail boat to go with!

I apolygize for taking so long to response to all the great advice and it is truely appreciated, thanks to every one.

Tbeargladd


----------



## TSOJOURNER (Dec 16, 1999)

*Conversion*

Jeff_H,
I am curious about the conversion that you spoke of. I am currently looking at a Perry design that could be ordered either way. The majority seem to be deck stepped, but one of them that I am looking at is keel stepped. Someone on this thread mentioned that the deck stepped mast is typically a stronger extrusion than a keel stepped one would be. If this is the case, would it be wise to lop off the bottom and make it deck stepped. Perhaps this is not the case, i guess I would have to get more info on the mast itself before making that decision.

Thanks,
Kenyon


----------



## sailingdog (Mar 19, 2006)

kenyonstewart said:


> Jeff_H,
> I am curious about the conversion that you spoke of. I am currently looking at a Perry design that could be ordered either way. The majority seem to be deck stepped, but one of them that I am looking at is keel stepped. Someone on this thread mentioned that the deck stepped mast is typically a stronger extrusion than a keel stepped one would be. If this is the case, would it be wise to lop off the bottom and make it deck stepped. Perhaps this is not the case, i guess I would have to get more info on the mast itself before making that decision.
> 
> Thanks,
> Kenyon


The *deck-stepped extrusion *is generally a heavier one than a *keel-stepped extrusion* for the same boat. *There is nothing to LOP off of a deck-stepped mast, as it is already deck-stepped. *Trimming a keel-stepped mast to make it a deck stepped mast is not recommended and fairly unwise. There's a fair bit of engineering that has to happen to convert a keel-stepped mast into a deck-stepped one. A compression post of some sort has to generally be fitted. The hole for the mast has to be properly filled, and then a proper mast step has to be put in place, and tied to the compression post.


----------



## hellosailor (Apr 11, 2006)

Unmentioned is mast rake. A keep stepped mast can often be adjusted for mast rake, a deck stepped mast can't be. Or course, if the boat was perfectly rigged and balanced, you wouldn't be messing with mast rake but on some classes (like J/24) it is just one of the normal options to tune for any given day of racing.


----------



## Jeff_H (Feb 26, 2000)

Sailingdog, you are mistaken when you say that a keel stepped mast is a lighter estrusion than a deck stepped mast. The way that keel stepped masts are actually designed, in theory this is exactly backwards. In designing keel stepped masts for cruising fiberglass boats, we engineered the lower mast panel length as if the deck provided zero support (otherwise the deck had to be engineered specifically for the side loads, which they weren't. Soft wedging was required to minimze the load transfer.). Because of the greater panel length, keel stepped masts actually came up requiring bigger moments of inertia and a bigger section modulus, in other words a bigger spar section. In reality, there are a limited number of spar sections on the market and we generally rounded up anyway, so in practice it would not result in a larger spar section for a keel stepped mast even if the calc's said that the loads were greater. 

In any event, what that means is that you could lop off the bottom of most keel stepped masts and make a deck stepped mast. This is especially true if you design the decked stepped mast with a moment connection to a section of spar below the deck as I have proposed in the past, in which case the load distribution would be virtually the same as a keel stepped mast that was rigidly blocked at the deck. 

With regards to mast rake and deck stepped masts, in practice that is easily resolved by small amounts of shimming of the maststep or mast butt. 

Jeff


----------



## TSOJOURNER (Dec 16, 1999)

Thanks, Jeff_H that answered my question.

Also, mast rake on a deck-stepped mast can be adjusted just like a keel-stepped mast. I have raced small boats for years and have lots of time racing on J22s, SR 21s, Hobies and Catalina 22s which are deck-stepped and one can easily adjust mast rake. On most racing setups, at least a few inches of pre-bend by ajdusting the lowers is desireable. Then, use the adjustable backstay to add more when needed.


----------



## TSOJOURNER (Dec 16, 1999)

Jeff,

We are fixing up our boat for extended cruising. As there is not a lot of space below, someone suggested that we have the mast cut, stepped on-deck, and have a compression post put in, thus giving us more space. I shrugged this off assuming that a professional rigger would tell me I am nuts.

Did you have this done? If so, could you give an idea of the costs involved?

Thanks,
Hubans


----------



## Giulietta (Nov 14, 2006)

That's a weird thing you're saying...

What difference does it make space wise to cut the mast and install a compression post???

Its the same...where do you save the space??

Besides, you will have to recover the cabin, where the mast now protrudes, spend a whole lot of money, I see no benefit...but that's just me.

I wouldn't do it...peace of mind...


----------



## sailhog (Dec 11, 2006)

Giulietta said:


> That's a weird thing you're saying...
> 
> What difference does it make space wise to cut the mast and install a compression post???
> 
> Its the same...where do you save the space??


It's not a space issue but a safety issue. Say the mast is made of wood, it can cause you to get splinters in your ass when used as a stripper pole, or even cause your g-string to snag. What you want is a nice, smooth chrome compression post for this kind of work.


----------



## TSteele65 (Oct 19, 2006)

sailhog said:


> It's not a space issue but a safety issue. Say the mast is made of wood, it can cause you to get splinters in your ass when used as a stripper pole, or even cause your g-string to snag. What you want is a nice, smooth chrome compression post for this kind of work.


Don't forget the Windex (you never know what the previous dancer left on there).


----------



## BlowinSouth (Nov 10, 2007)

Good one sailhog!

I've always had keel stepped masts, not really for any particular reason other than thats the way the boat that I bought was designed.

I have always had a nightmare vision of in the event of a roll over the mast inside the boat swinging all around in a "straw in a cup" fashion like trying suck up the last drops of milkshake. I don't think I'd want to be down below in that did happen.

Not sure if it would happen but seems plausible enough to be a concern.


----------



## Giulietta (Nov 14, 2006)

BlowinSouth said:


> I have always had a nightmare vision of in the event of a roll over the mast inside the boat swinging all around in a "straw in a cup" fashion like trying suck up the last drops of milkshake. I don't think I'd want to be down below in that did happen.


How small is your mast???

Or how suction wise are the folks around you??

I met a girl once that could suck a golf ball thru a garden hose, but someone that can suck milk out of a boats mast must be nice to know...


----------



## Tartan34C (Nov 21, 2006)

Jeff_H said:


> Sailingdog, you are mistaken when you say that a keel stepped mast is a lighter estrusion than a deck stepped mast. The way that keel stepped masts are actually designed, in theory this is exactly backwards. In designing keel stepped masts for cruising fiberglass boats, we engineered the lower mast panel length as if the deck provided zero support (otherwise the deck had to be engineered specifically for the side loads, which they weren't. Soft wedging was required to minimze the load transfer.). Because of the greater panel length, keel stepped masts actually came up requiring bigger moments of inertia and a bigger section modulus, in other words a bigger spar section. In reality, there are a limited number of spar sections on the market and we generally rounded up anyway, so in practice it would not result in a larger spar section for a keel stepped mast even if the calc's said that the loads were greater.
> 
> In any event, what that means is that you could lop off the bottom of most keel stepped masts and make a deck stepped mast. This is especially true if you design the decked stepped mast with a moment connection to a section of spar below the deck as I have proposed in the past, in which case the load distribution would be virtually the same as a keel stepped mast that was rigidly blocked at the deck.
> 
> ...


Jeff H,
It appears that you have a different system for the calculation of the required moment of inertia of the mast section. The standard way seems to be to consider the deck stepped mast as a pin ended column and the keel stepped mast to be a column with one pin and one fixed end. Skene's gives the example of required transverse moment of inertia as Constant X Lt^2 (in X 10^4) X (Load X 10^4). The constant he recommends for aluminum is .94 for keel stepped and 1.41 for deck stepped masts. The keel stepped spar is much stiffer so it can have a lighter section. In practice it may not because the keel stepped designs tend to be heaver boats with stronger rigs in proportion to their length and weight.

Henry and Miller in a paper presented at SNAME go at it differently and apply a more rigorous solution based more closely on Euler's column formula. They use a column factor (K) of 2.25 for keel stepped and 1.8 for deck stepped masts. They also see the mast as either a pin end or fixed and pin end column.

Hubans,
The change you are contemplating needs to be blessed by someone that know what he is looking at. Changing a keel stepped mast to a deck stepped one by just cutting the mast at the deck may require a different section and that means a new mast.
All the best,
Robert Gainer


----------



## sailingdog (Mar 19, 2006)

According to most of what I've read Jeff, deck-stepped masts are thicker walled than keel-stepped masts of the same height above deck.


----------



## TSOJOURNER (Dec 16, 1999)

> If a keel stepped mast corrodes at the keel how would a survery be able to diaganose if their is structural problems with the mast and keel?


The corrosion hazard is pretty minimal, unless you end up with some kind of stray current running through the spar. It would not be too difficult to spot or detect with a hammer.



> Is their a life expectancy of a mast before it would need to be replaced and if so what is the expectancy? Like the standing rigging, suppose to be good for up to ten years! True/False?


 Varies from boat to boat and mast to mast. Ten years is early for (most) masts.



> If a deck stepped mast doesn't have a compression post and the mast has concave the cabin top, would that area on the cabin top have to be cut out and replaced or would the entire cabin top have to be replace or some type of support would be just enough to give the sunken portion of cabin top some lift to its normal stature?


The correct thing to do in this case is nothing and allow whatever fool is out there sailing it to continue until he meets the fate he deserves...  (_just kidding_) It will vary from boat to boat, but I don't think that any craft will support a deck-stepped mast without a compresion post for very long. It would probably cause significant damage quite quickly.



> When I see a "rubber boot" (I hope that is the correct terminology) at the bottom of the mast is that what protects the Keel Stepped Mast from leaks into the interior or does this assist the Deck Stepped Mast from water softining the cabin top?


 The boot is there to keep water out. I have a keel-stepped mast, with a boot, and Spartite, which is a compound used to support the mast and seal the hole. The Spartite does an EXCELLENT job of keeping water out as it forms a plug in the track, which is the primary source of water ingress. It also replaces the mast wedges thereby removing a lot of high-stress points on the mast and serves to evenly dissipate a lot of the wind's force throughout the deck structure.

For an illustrtation of this, take a drinking straw and poke it through a hole in some cardboard. Make the hole a little bigger than the straw. Now push hard against the straw from one side, and it will probably bend where it meets the cardboard.

To see the effect that Spartite has, take the straw out of the hole in the cardboard, and then wrap some tape around it until it fits very snugly into the hole in the cardboard. You'll see that it is much hard to bend it, because the tape prevents the straw from flattening easily in that area.

The Spartite functions in the same way that the tape does, so if you end up with a keel-stepped mast, I would recommend that you invest in the Spartite as an added safety and comfort measure.



> As many boats as their are that are Deck Stepped the amount over shadows the amout that are Keel Stepped, other words I see more Deck stepped than I have seen Keel Stepped. Does that have any affect of the value of the boat?


 No. The variance is due to a decision made by the designer. A lot of people have a preference for one or the other, but unless an amateur modification has been done to change the boat from one form to another, the boat's value will be calculated on it's overall condition and desirability in the marketplace.


----------



## sailingdog (Mar 19, 2006)

One corrosion problem that can be serious with a keel stepped mast is if the keel's mast step and the mast foot are made of different materials. You can have serious galvanic corrosion issues if the bilge is at all wet. This is usually pretty easy to spot though.

Mast boots often only reduce the amount of water that comes in with a keel-stepped mast. Often, the mast will leak water into the bilge, since it may get water in through the various opening on the spar. The mast boot only prevents the water from coming down along the outside of the spar. 

Many boats with a deck-stepped mast have a compression post. Others use a bulkhead or a beam to take the compression loads. In any boat with a deck-stepped mast—it is important to make sure that the load bearing/transfer structure within the hull is in good shape. The best compression posts are either aluminum or stainless steel. Wood is not so good, since it can rot more readily than a properly designed aluminum or stainless steel compression post will degrade. 


Personally, I prefer a deck-stepped mast, as I believe it does help keep the cabin drier and presents less of a hazard in the case of a dismasting. YMMV.


----------

