Gougeon Wing Mast Plans

Discussion in 'Multihulls' started by HydroNick, Apr 4, 2010.

  1. ThomD
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    ThomD Senior Member

    It is an old thread, but a few notes anyway:

    When it comes to all this liability and engineering, which I am sure are correctly summarized, it does depend on the aspect ratio of the spar. The gougeons were long proponents of efficient rigs and hulls. But on most high performance boats it seems as though they get more extreme all the time. Are you looking to set the world on fire, or make a practical rig for a simple boat, preferably a multihull with a wide staying base.

    So to throw out more leads:

    Article on the famous Gougeon/Watson built ply and core mast for Atom (not the commercial design):

    "This boat sports an experimental wing mast constructed of 1/16″ thick aircraft birch plywood outer skin, 1/64″ thick plywood inner skin separated with 1/2″ Tricell H™ (resin impregnated paper) honeycomb. It was fitted to the boat five years after initial launching. With some reinforcing stringers, this laminate stack was lightly vacuumed while flat, then folded and placed into a form to establish an airfoil until all cured. An aluminum bolt rope was simply bonded into the back end slit from which the vacuum bag was removed. Mast hound was a stainless steel plate with threaded rod passing through it into localized wood and unidirectional carbon fiber buildup. The result was a very light section that has proven very efficient. Despite several stepping accidents, the structure stands to this day."

    Gold coast yachts:

    Not really any specifics but they were proponents of a 2-1 spar section (probably also the Atom mast is fat, you can't get a 3-1 section in a single fold without s leading edge seam). They used 1/2" wood strip, and 10 oz glass, from what I have heard of one set of scantlings. Localized re-enforcements of carbon would probably be necessary. The 2-1 section seems to be more sensible when it comes to cruising, or handicap racing. The 3-1 gougeon section is famous for basically being a small sail at all times. In area like a storm sail, if you are lucky.

    Meade on revisions to Adagio (quoted from Epoxyworks as also above):

    Building a new wingmast

    "The original wing mast had always seemed marginal when pressed hard in heavy air. We’d built it light (120 pounds for a 39-foot mast without hardware) and it had never failed. It may have lasted many more years, but with modern sail technology imposing more loads on a rig, we decided to build a new wing mast.

    We built the original mast using a fold-up plywood construction technique, which became the basis for many more built since. It is a simple and quick procedure that results in a good product for the time and money involved. However, this time around I wanted to build a state-of-the-art wing mast that would be stronger, stiffer and smaller in section than the original, and weigh less. The original section was 17 inches in chord length with pointy leading and trailing edges, which are inherent in “fold-up” construction. My primary goal was to reduce the chord length to just 12 inches but not give up any precious edgewise stiffness; one of the advantages of the rotating wing mast concept. My other goal was to adapt a larger leading and trailing edge radius. The resulting smaller section would be less adversely affected by wind when moored, or at the dock.

    A new building method allowed us to accomplish both goals. It was relatively easy and did not require a lot of man hours. Our strategy was to separate the mast building effort into four separate parts; two molded side panels and two more molded sections, one for the nose and one for the tail. We made all four of these parts on two simple, easily fabricated molds. For the nose and tail parts, we used 3-inch diameter PVC pipe. We used a simple, curved plywood mold to make the side panels.

    To build the nose and tail sections, we used Unidirectional Carbon Tape sandwiched between a 4-inch wide woven 9-ounce glass tape. This allowed us to achieve 60 percent fiber weight in a wet lay-up, without any vacuum pressure. The total weight was 14 pounds for each 40-foot long section.

    We laid up the side panels with 0.1-inch Douglas Fir veneer sandwiched between layers of 5-ounce woven carbon cloth. In the center area of the 10-inch wide panel, we concentrated further layers of Unidirectional Carbon Tape for an all-up weight of 28 pounds per panel. To consolidate this more complex laminate and achieve a light weight, we used vacuum pressure on the side panels.

    For temporary clamping pressure, we set up one of the side panels in a simple fixture and held the leading and trailing edges in place with sheet metal screws. Then we installed the sheer web (see photos) and the other internal pieces and parts that support the tangs, hounds, halyards and the other complexities of a modern mast system.

    The benefit of this new construction approach over the older fold-up method is that you can deal with the interior complexity at your leisure, then complete the mast by bonding the opposing side panel in place.

    With the mast structurally complete, we needed only to fair in the bonded joints and add some strength on the exterior of each joint with 2-inch glass tape. After final fairing and finishing, our mast weighed 105 pounds. With all the hardware, rigging and halyards in place, the new mast weighs 132 pounds."

    Of course they don't say exactly what the schedule is, but if I was building a smaller less stressed boat, and I could probably reverse engineer it from those numbers. There are also some standard haircuts when you move from cedar to Al, and Al, to carbon. I forget what they are for stiffness, but it probably run from something like 1/16 for carbon (or whatever you have to do to make the structure tough enough), to 1/4 for al, and 1" for wood. Just stuff you pick up when designers provide alternatives for materials.

    Keep in mind that the Gougeons have an engineering department...
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  2. oldmulti
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    oldmulti Senior Member

  3. garydierking
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    garydierking Senior Member

    I built two 60' Stressform wing masts back in the day. 4mm birch ply, spruce spars with carbon uni, strapped together with plastic banding for curing.



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  4. Eric Sponberg
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    Eric Sponberg Senior Member

    Thanks for your contribution. Aspect ratio (chord/section thickness) of the section can be whatever you want it to be, and then engineer the mast accordingly. Typically, the higher the aspect ratio, the more difficult it is to trim the mast into the wind, particularly with a wind gradient rising from the sea surface. The angle of attack required at the top of the mast will be different than at deck level. Flow separation can easily occur if not trimmed properly. With a shorter chord (smaller aspect ratio) the section is fatter, the nose section more full, and so the tendency for flow separation is a lot less. An aspect ratio of 1/1 is a round mast, and the more typical large aspect ratio is 3/1. I have always been an advocate of 2/1.

    In the description of the Gougeon Wing above, the 1/16" outer skin and the 1/64" inner skin, to my mind, is a very unbalanced laminate. It would be more structurally sound if the skins were the same thickness.

    The Gold Coast Yachts favoring a 2/1 section was present during my consulting with them on their mast engineering and design back in the 1980s. We thought along the same lines and did not see advantages to changing that aspect ratio.

    To switch between materials--wood to aluminum to carbon--the engineering requires equivalency of the factor EI, where E is the modulus of elasticity of the material, and I is the geometric moment of inertia of the section. I is different fore/aft vs. sideways, so the engineering has to be clear as to which you are using. I always engineered my wingmasts to the sideways bend as that was the weaker of the two directions. That is, if you design a wingmast out of wood, calculate the EI of its mast cross section. To switch to aluminum, E will go up by about a factor of 5 over pure wood, and by about 20 over plywood (you lose a lot of modulus when using plywood). So I can come down accordingly until EI is the same. To switch to carbon, the E of a carbon laminate is about the same as aluminum, maybe 10%-12% more if built well, and then I can shift down slightly in like manner. The thing is, carbon fiber is about 60% of the weight of aluminum, so right away there is a weight advantage going to carbon over aluminum.

    Reducing I means you are reducing the section shape and possibly the wall thickness. However, in my mast studies and designs, there is a danger of making wall thickness too thin. Too thin a wall, no matter what material, can lead to premature buckling of the mast section, before the stress reaches the maximum capability of the material. In my carbon fiber mast designs, I always strove for a skin-thickness/section-thickness ratio of 0.03 (or 3%). By keeping wall thickness at least that much, then I felt that the mast would be safe against premature buckling. This is based on a lot of years breaking and studying full size pole sections.

    I hope that helps.


    Eric Sponberg
    SY Corroboree
    Townsville, Australia
    (about to continue voyaging across the Indian Ocean this year, 2021)
  5. ThomD
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    ThomD Senior Member

    Quite the address you have going for you there Eric, since this thread last received oxygen. Must be some good stories there. Thank you for your elaboration of the formulas on carbon. I spent a good deal of time in the early internet years talking about how carbon blows up stuctures based on the idea that a little carbon added here "can't do any harm". I was lucky, one might say, to make some unwise structures for canoes before getting myself into more comprehensive trouble. And based on a rather thin experience, none the less managed to stay out of trouble.

    Careening off topic...

    At this point with some access to materials problems I am thinking of buying a roll of 6 oz carbon cloth and making some unwise decisions again. I wonder if anyone knows what happens when you slug the standard carbon "boatcloth" at decent 1088 plywood. The only metric I know of is the one Meade laid down when he said that as a panel, 3/8" cedar strip and 6 oz carbon uni on both sides aligned with the 90, played like 1 inch d-fir plywood in the hydromat. I am talking backyard boatbuilding, maybe at some point getting back to the JanCat 24 problem. What does plywood with a layer of carbon "boatcloth on each side play like. On say, 4mm, 6mm, 9mm? Would 4mm = 1/2". Any guesses? Not talking about Team Phillips' beams, or a wing spar that turned out inefficient because it poked out of the atmosphere... Any guesses? It's Canada, you can never get even the simplest things without a struggle, and then someone hands you a roll of carbon uni and sparks start flying about using some carbon and plywood like Strings....
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  6. ThomD
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    ThomD Senior Member

    By the way, very helpful, forgot to say above.

    I can only imagine that the reason they used the ply schedule they did, given that as we all know, this was not their first rodeo, was because that was as beefy as they could make it and get the fold they wanted. Reading between the lines, it would seem that the Atom spar was very similar to a gold coast, in that there would have been stringers between the ply at the nose, the max chord position, and the trailing edge, the only place where the actual core and ply would have been in play would be in fairing portions of the spar. A risk would be the separation of the plywood plies, but everything else load bearing would have been pretty linear. It is sorta like the Gold Coast strip spars with pared back on strips in the areas that are more for fairing, than load bearing. Though it isn't clear what kind of a workout it would have taken in it's home range. You can work a spar a lot just sitting on a mooring vs a trailer, or a very well sheltered Great Lakes port.

    A good tip for wing mast cruisers and posers ( as opposed to people who can actually quantify this stuff) is to consider the role of stronger or more linear woods than those in the usual boat building arsenal. There is the birch aircraft ply, (The Gougeons do not seem to have shied away from using doorskins in some boat parts, back when they were pristine and used at least some real glue). They could have also made the stringers out of stronger wood, or aircraft graded wood, not the usual trash we employ making wood multihulls. The aircraft standard is 1) graded, and 2) about 2-3 times as strict on runout as the boat standard, which isn't graded at all. One could simply use stronger woods, though it could be counter productive in a situation where the main play it to load up the carbon inside the tube. It wouldn't be a Gougeon product without some successful, but baffling use of Tricell. But just a gentle reminder that not everything has to be cedar.
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  7. ThomD
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    ThomD Senior Member

    At least with cedar you can see the growth rings. Some of the tropical woods like mahogany. without growth rings are a bit of a mystery as to grain runnout. So a spar, be it beam or mast, is a good place for some transparency as to the actual grain runout. There is a difference between color, figure, and grain, and only a reliable read of the latter is going to tell you about runout. You can sense it without seeing it, with destructive test of offcuts (just randomly snapping some of the twigs, or through tools like hand planes that offer a lot of feedback.

    Hands up everyone who knows that each and every graded wooden arrow is graded visually for runout, which is roughly 1-100, not 1-8 as with boats, and 1-20ish for aircraft. And it is also measured for modulus of elasticity (if that is what you get with a deflection test) within 10%; and classified within 1% groups on weight. And in use, each arrow is then aligned with the growth rings perpendicular to the load path, and the runout is also aligned with the load path. That is the kind of standard that is optimal to get good results, and not end up tattooed with a broken shaft in your hand. But it is an example of how far you can take it, while cassually sorting through a series of sticks without hardly paying attention. Just a process.
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  8. ThomD
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    ThomD Senior Member

    I would like to see that information, now that it is no longer a commercial situation. The scantlings were release for that spar on the Tremolino Yahoo Group decades ago, but the full treatment would be great. Some of this stuff now needs to be preserved historically. The Gougeons did super interesting stuff, but did not want to displace designers, so they left a ton of their legacy buried.
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  9. Richard_F
    Joined: Aug 2022
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    Richard_F Junior Member

    Hi! Garydierking, wow I was looking for something like that, I was just asking that right now on this other thread.... Wood-fiberglass Mast (ideas to improve it in 2022?) https://www.boatdesign.net/threads/wood-fiberglass-mast-ideas-to-improve-it-in-2022.67531/page-2

    I really appreciate if you can provide more detains for the 60´ mast, I´m looking to build a 20 meters mast for a trimaran.

  10. MichaelRoberts
    Joined: Sep 2015
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    MichaelRoberts Archimedes

    Maybe this will help/inspire
    About six layers of uni and bi-ax carbon on 1.5 mm aircraft ply bent over ribs and stringers
    The mast is slightly fatter in the middle then tapers to the top
    All ribs generated by Rhino and CNC cut - they fit on one sheet of ply
    Many years of engineering went into this 20 metre rotating wing
    Many thanks to people on this forum plus A J Marchaj and Frank Bethwaite
    Mast ribs assembly enhanced and cropped.jpg Nested mast ribs.jpg

    Attached Files:

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