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Thread: Skin On Frame Hull Covering

  1. #1
    Join Date
    May 2011
    Posts
    28

    Default Skin On Frame Hull Covering

    Good morning boat builders! My name is Larry LaLonde and I'm the new owner of Geodesic Airolite Boats, purchasing the company from Bette Monfort when she retired in October. I started a thread yesterday in the Design/Plans forum explaining my history with SOF boats, with Bette and that these threads are to help all of us build better boats by developing a "knowledge base" about SOF building. There was a lot of positive response and several suggestions about how to proceed.
    I encourage all of my new customers to join the WBF so they can get some perspective beyond my input. As a business owner, I understand there is a fine line here at WBF between promoting my business and sharing information and I won't cross that line. Please let me know if I do but the purpose here is to help all of us build better boats. One of the responses yesterday suggested I start specific threads in this forum so we can start focusing the responses to specific issues so here goes.
    SOF hull coverings are discussed in many threads over many years throughout the forum but the hardest thing to find is follow up by someone who has used some specific method and how it worked. If you're familiar with Platt Monfort's work, he dedicated a lot of time and creativity toward finding a way to make the 3.7 oz. Dacron tougher and I don't think he was ever really happy with his results. Full disclosure; I've only built one boat using the 3.7 oz. Dacron, a solo boat for my wife and several years later it's holding up very well, much tougher than I expected. However, my other six boats are all "proof of concept" boats or test platforms for my own use. I'm 6'4", 200 pounds and I don't baby my boats so they are built using heavier Dacron I got from Jeff at Kudzu Craft or from George Dyson. I've developed methods to make Dacron much tougher and I'm looking forward to sharing and discussing those and other methods as this thread develops.

    Larry

  2. #2
    Join Date
    Feb 2006
    Location
    Pennsylvania
    Posts
    8,027

    Default Re: Skin On Frame Hull Covering

    Picking up from the other thread, my next SOF boat will use 8 oz nylon but with a different coating. I used Spirit Line's "goop" or 2-part urethane. The good side of this material: it's agreeable to work with -- no powerful toxic odors. When cured it's extremely tough and remains flexible, even at freezing temperatures, and it bonds to nylon very well.

    The negatives -- it turns yellow over time, seems to be UV exposure that does this. It's thick when applied and very hard to get a nice clean finish all around. Once it cures, there's no way I could find to adjust -- if you have a drip or a run it's there to stay. There are dyes available, but judging from the instructions it's a trick to get good results -- and I've seen boats made by others that confirm this suspicion.

    So what's best? Dave Gentry has worked up a system. I'll let him explain that. I made up a sample with Flex-Seal gutter sealant. It's available in several colors and is very easy to spray on the fabric and then work in with a squeegee. There are similar products by other manufacturers. I'll be looking more into this for my next SOF project.
    -Dave

  3. #3

    Default Re: Skin On Frame Hull Covering

    3.7 oz seems kind of light weight but I notice you recommend two layers. Are two layers of 3.7 stronger than 1 layer of 8oz?

  4. #4

    Default Re: Skin On Frame Hull Covering

    Forgive the beginner questions but I was wondering the following:

    1. When using two layers of fabric do you apply one, heat shrink it, then apply the second?

    2. Does the Flex-Seal penetrate through the fabric or form a shell on the surface?

    3. Could I apply 1 layer of fabric, shrink it, apply the Flex-Seal, then add another layer of fabric, shrink it, and then paint it?

    4. Would this "sandwich" technique give me the benefits of a stronger more waterproof structure while still allowing me to apply a decent painted surface?

    I was thinking of getting a yard or two of fabric, some paint, Flex-Seal, and then constructing a few simple frames and testing the various ideas out. See how they hold water, resist punctures, etc.

  5. #5
    Join Date
    Feb 2006
    Location
    Pennsylvania
    Posts
    8,027

    Default Re: Skin On Frame Hull Covering

    Jaxenro, This is all in the experimental stage as far as I know. I don't know that you'll get any solid answers based on long experience because new materials and coatings are being tried all the time. But first, keep in mind different cloths are used -- there's aircraft dacron which is a light material, various weights of polyester and various weights of ballistic nylon. The polyester and dacron can be painted; the nylon won't take paint.

    From my own experience I can tell you that thinner materials like the spray-on Flex-Seal don't soak into nylon deeply, but by spreading the material with a flexible plastic spreader it will work right into the material and it's easy to get a smooth clean finish. The thicker goops don't do this. On polyester you can build up layers of paint. This is easy to do but I've found that in freezing cold weather the paint surface crazes beacause there's not enough flex in it.

    I've never tried overlapping two layers of cloth. I would expect it to be difficult to get a neat seam if the edges were sewn together. If stapled and then covered with trim, that part probably wouldn't be an issue. No idea what makes for a good coating schedule.

    FYI, many years ago I covered a kayak with the light aircraft dacron, which heat shrinks very well. I glued it on with the glue that's sold for airplanes and it was easy to put on a second layer along the keel as a wear strip. This also saved some time sewing up the cover and made for flat seams. I haven't heard of anyone gluing on a kayak cover for a long time, but it's another avenue that could be explored.

    So please, experiment and report back!
    -Dave

  6. #6

    Default Re: Skin On Frame Hull Covering

    I was basing this on what I read on the GABoats site and here. The cloth they use is a 3.7 oz Dacron and they recommend two layers. From the looks of things they glue down the edges with heat activated tape then shrink the Dacron. Then the rub rails etc screws in over the edge to further hold it down. So my thinking was to make a sandwich with the rubberized coating (flex seal) between the two layers. All things being equal I think this would be stronger than one layer as both layers would need to be punctured yet a glancing blow might only rip the outer layer

    like I said I will make up a few test panels and do some punch tests and water holding tests

  7. #7
    Join Date
    Feb 2006
    Location
    Pennsylvania
    Posts
    8,027

    Default Re: Skin On Frame Hull Covering

    These fabrics are all stronger than oughta be expected. I had one layer of 3.7 oz cloth on a big tandem for about 5 years and never managed to put even a tiny hole in it. The 8 oz. ballistic nylon is pretty near bulletproof. One of the really big advantages of SOF construction is the light weight achieved. There's a risk of killing that if more layers of cloth and goop are used than is necessary.

    When you make up your samples, go at them with claw hammers, crowbars, drop rocks on them from high up, whatever you can dream up. You can puncture these materials with an awl or similar, but they still don't tear. A roll of duct tape will fix anything well enough to get you home.
    -Dave

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