Gougeon Wing Mast Plans

[Eric Sponberg]

Stressform was a marketing name by the Gougeon Brothers for their stayed, wood-epoxy wingmast designs. After some years of selling plans, they gave the business over to Georg Thomas, who had some mast building experience, because the Gougeons were afraid of the potential liability. I think they found that the mast designs were being used for boats that they weren't intended for, or that people weren't following the plans properly. At any rate, the liability exposure was enormous, and they just could not accept that any more. I don't know what has happened to Georg Thomas and the Stressform designs--maybe he came to the same conclusion. If the mast breaks and kills somebody, the designer really is on the hook, no matter what the plans say.

The liability, indeed, is enormous--this is why I do not design stock plans for masts, and it is mostly likely why you are not finding many, if any, stock mast designs. The mast designs that I create, and the laminate schedules that go along with them, are designed strictly for the boat at hand. They are highly dependent on the skill of the builder/owner and on the availability of the materials at hand--the carbon fiber and the epoxy resin. The length, section shape, taper, wall thickness, strength and bending characteristics are all tailored to the boat's sail plan and righting moment. What works for one 40' sloop likely will not work for another 40' sloop.

To create a mast design and it's laminate schedule, I need to know which carbon fiber fabrics the builder/owner is going to use. I can specify what I think will work, but if the builder/owner can't get those fabrics (and the carbon fiber market is still very volatile in that regard) then my design is useless. Same for the resin--it has to be readily available and be appropriate to the task at hand. Finally, the laminate really must be laid up under vacuum bag to a minimum 50% fiber content by weight, and the mast has to be post-cured in an oven (a make-shift temporary oven will do), and the temperature of the laminate should be monitored during post cure to guarantee the post-cure temperature of the mast. All this takes a lot of skill and preparation, and it is why mast design and construction is a pretty complicated process. A fault in any link in this process can lead to mast failure and a resulting dangerous situation out at sea. Going through the process with the builder/owner as his design is being developed gives each of us the assurance that the mast will be built properly. You don't have that assurance with the sale of stock plans that just anybody, who may not have the necesary building skills, can buy.

Eric

[rob denney]

Originally Posted by Timothy

Hi Rob I talked to you a couple of years ago about new masts for my Freedom 40 but at the time you were still developing the process for building carbon fiber masts that would be affordable. I would like to know more about building a freestanding wing from two vacuum bagged panels. Did this come out of the work you did with the kiss system? Could you use resin infusion for the panels? How do you design the mast so that it tends to bend more readily along the long axis to flatten the sail? I know that Eric Sponberg used tubular or box like structural elements with non load bearing fiberglass fairings for leading and trailing edges partly to make it easier to predict mast bend. But I think I read that on his latest mast to reduce weight he used an elliptical section with the wall laminate adjusted for bend. Others have used luff pockets on tapered tubes. I believe Team Philips used panels joined with flexible membranes and a complicated sail track arrangement that collapsed into itself when under compression. You mentioned cores . I think I also read that for wall thicknesses of free standing carbon masts there is no weight saving using cores as apposed to using solid laminate of a greater thickness as with no compression loads buckling is not a problem. I have as yet not replaced my masts and the more I read the more discouraged I get that I can build them myself and achieve the weight reduction and efficiency I am hoping for. I would be interested as to how your new mast turns out and weather or not a home builder using your plans might expect to build a mast close to the weight of an autoclaved one. I am fortunate that I can enlist the help of my friend and next door neighbor here in Thailand who is an expert in composites and has worked all over the world setting up production schedules. Right now he is doing the new infused carbon F18 hulls at Cobra.

You will have a long wait for me to finalise any build method! There is always a new idea to try. The wing from flat panels uses infused panels but has no cutting or shutting to get the shape, so is not much like KSS. All my panels are infused, but that is because i have an infuser with a big table next door. Could just as easily hand laminate and vacuum them which would use less material, but not have the luxury of time to get everything set up. I get the wing shape by varying the laminate. Have just built a pair of rudders using the same technique.

I assume the wing mast will bend very little along the long axis. Sail shape is altered by rotating the mast, not bending it, except for the depowering that happens when it bends sideways. Making it bend fore and aft is an engineering problem, but to me it defeats the purpose of the wing.

For a tube mast, core does nothing except add weight. At some chord dimension, it becomes a panel stiffness problem and core is required. On my 600 mm chord mast it is 3mm, on the mast for a 7 tonne 20m proa it is 6mm, so not much weight. At some chord thickness a sheer web is also required, which adds to the complexity of the build, but not the difficulty.

We have no problem sourcing the carbon for my masts. I use tow, but you could replace it with uni if you don't want to build a wet out machine. I am still trying to figure out the best way to use tow in infusion, so for this, uni would be better. I scored some cheap carbon cloth so will be using that for my mast, but our cruising masts use glass for the off axis loads which reduces the cost significantly, at the expense of a little weight. I am using vinylester for the infusion, but would use epoxy for hand lay up for the longer out time and no horrible smell.

One of the big advantages of an unstayed mast is there is only one thing (the mast) to break. Therefore, it can be bench tested to quite high loads (the limit is usually supporting the mast at the bearings) and the deflections compared with the engineers numbers. If they are the same, you won't have to worry about the mast breaking in normal use. There are so many reasons for a mast breaking, that I find it difficult to believe there is a liability problem for a designer although I can understand a negative publicity problem. I don't know of any mast designer who has ever been sued, successfully or not. Have there been any?

Building your wing masts is easy enough if you have a long table, a vac pump and know how to follow a string line. I am still waiting for the infusers to finish their 15m table, but my mast is the first job when they do and there will be photos of it's build on my web page. Should be some rudder ones next week as well. You will not match autoclave results unless you pressure compact your mast. This is easy enough with a round mast and a (cheap(ish) steel mould, but not with vacuum. The weight difference will be insignificant compared to vac bagging. Much less than the weight of a bolted on alloy sail track compared to an integral carbon one.

The hardest part of building a mast is getting started. If you buy a sheet of glass say 1m sq and a vac pump (your mate next door should have both), I will send you the approx layup and measurements for a section of mast which you can infuse and build. The only difference between doing this and doing it full size is the need to follow the string line.

Nick,
they were very expensive, hard to build, over engineered and relied on partial vacuum to make the panels thick enough not to buckle, which scared the crap out of me.

rob

[idkfa]

Good article on rig design from http://www.aes.net.nz/

http://www.aes.net.nz/Rig%20Design%20Commentary.html

Down towards the bottom "Home Made Carbon Masts" gives a fiber layup schedule.

[idkfa]

Another good article:



...............When a bending overload occurs the El equivalence between our carbon mast and the aluminium mast goes out the window since a stress concentration occurs at the partners. This means that our primary loads are no longer shared throughout the cross section of the mast but rather are being concentrated in parts of the section at the partners. If these loads exceed the capability of that small area then that area will fail locally. Local failure usually leads to global and down comes the mast.

Why has failure at the partners not been an issue in aluminium masts? Go back to our El equivalence and you have your answer. Since the aluminium mast has a lower E the I needs to be higher which translates to a thicker wall by around two times. The local stresses generated by the partners are thus distributed over a greater area reducing the opportunity for failure. However, when you produce the carbon equivalent the El requirement generated by the proven aluminium design leads to a reduction in wall thickness of two to three times. Suddenly the loads from the partners are being applied into a much thinner wall as well as being in the weaker load axis of the carbon laminate ........

[Eric Sponberg]

Originally Posted by idkfa

Good article on rig design from http://www.aes.net.nz/

http://www.aes.net.nz/Rig%20Design%20Commentary.html

Down towards the bottom "Home Made Carbon Masts" gives a fiber layup schedule.

The AES website has a lot of practical advice. However, the "fiber layup schedule" is a rough approximation and guideline at best--it is no substitute for a properly engineered design. Also, all of the discussion relates to stayed rigs, and there is not any discussion on free-standing rigs.

Many of the lay-up principles do apply to free-standing rigs, such as the use of all three fiber orientations--60 to 80% UDR, with some 0/90 and +/-45 fabrics. Whereas they recommend a 30/10 split between the +/-45 and the 0/90, I tend to make these an even split--20/20. If the percentage of UDR goes up, and I agree that 80% is an upper limit, the off-axis fibers reduce in amount in proportion, and I keep their amounts approximately equal. The other best advice on there is that the laminate should definitely stack in a mirror image through the thickness. I tend to keep my innermost and outermost fabrics the +/-45 instead of the 0/90 cloth.

Eric