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Re: foam sandwich retrofit question

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  • sirdarnell
    Peter you need approval to join. In any case, open celled foams can be saturated with water and sink (might take a long time.) Closed cell foams have gas
    Message 1 of 20 , Jan 2, 2011
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      Peter you need approval to join.

      In any case, open celled foams can be saturated with water and sink (might take a long time.)

      Closed cell foams have gas bubbles that can not be saturated with water, the areas between the gas bubbles can be, but because of the gas bubbles closed celled foams as a rule will not sink and thus make a better choice for flotation.

      David

      --- In bolger@yahoogroups.com, "Peter" <pvanderwaart@...> wrote:
      >
      > > What you want is one of the Urethane foams, not XPS.
      > > XPS is and open cell foam (eXtruded PolyStyrene.)
      >
      > There was an article long ago in Small Boat Journal about using an expensive foam to build a dinghy. It was an amateur project, and the design is clunky, but it may be instructive. The files are here:
      >
      > http://groups.yahoo.com/group/boatdesign/files/Dingbat/
      >
      > I don't think you have to join the group to see them. Joining isn't a problem in any case.
      >
      > There as a fad for this sort of construction back in the 1970s or thereabouts. It didn't catch on for amateurs. I think the problems of getting a fair surface outweigh any benefits.
      >
      > If the idea is to build a boat from fiberglass without plywood, another idea is to lay up glass panels on "table." The table would basically be a piece of thick ply with a laminate top, like a big piece of kitchen counter. You can lay up glass to the desired size, and the side next to table will be smooth as glass. Multihull designers Richard Woods and Derek Kelsall have built boats that way.
      >
      > A problem common to a lot of strong materials is that a panel that is strong enough is not stiff enough. Pure glass panels would require different framing than ply which is stiffer for its strength.
      >
      > Peter
      >
    • Peter
      ... I m the moderator, and I can promise approval will be coming within a day. I ll also see about posting elsewhere.
      Message 2 of 20 , Jan 2, 2011
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        > Peter you need approval to join.
        > http://groups.yahoo.com/group/boatdesign/files/Dingbat/

        I'm the moderator, and I can promise approval will be coming within a day. I'll also see about posting elsewhere.
      • KK7B
        I designed and built 3 different hollow windsurfing boards using 1/2 blue foam with an epoxy-glass skin about 15 years ago. Started with internal frames like
        Message 3 of 20 , Jan 4, 2011
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          I designed and built 3 different hollow windsurfing boards using 1/2" blue foam with an epoxy-glass skin about 15 years ago. Started with internal frames like an airplane wing, then with plank-on frame, then faired with 100 grit sandpaper, and finally a single layer of 4 oz glass and a sanding coat with West 410 microlight filler. They were beautiful, light (12lbs), strong, and fast. I logged hundreds of hours in big conditions on Lake Superior and in the Columbia Gorge.

          They were prettier than production boards by Mistral and F2 when new, but they didn't age well. Delamination between the glass skin and blue foam, despite 3 years of experiments to prevent it, resulted in big unsightly bubbles in the skin. Later production sailboards eliminated the deck seams, look as good as my custom designs, and last longer.

          My hollow sailboards were not nearly as strong as my Bolger-Payson instant boat construction with 1/4" plywood and a glass skin, but at a fraction of the weight. Because of the potential for gorgeous faired curves with no visible lines between planks, they invite a lot of hours of labor. I considered it time well spent--but that's a lot more work than instant boat construction using plywood.

          Thanks for the interesting question, and I sure thought about it a lot--but not so much after I failed to solve the delamination problem. I've never had glass-epoxy cloth delaminate from plywood.

          Best Regards,

          Rick

          --- In bolger@yahoogroups.com, "Christopher C. Wetherill" <wetherillc@...> wrote:
          >
          > All this discussion has brought to mind an old question I have been
          > pondering. Has anyone built an Instant Boat from 1/2" pink board with
          > fiberglass on both sides? Issues I have been considering
          > 1) easier to work than plywood
          > 2) slightly less costly than plywood
          > 3) not as stiff
          > 4) possibly lighter than plywood.
          >
          > I suspect that the need to glass both sides will result in no savings of
          > cost or weight.
          >
          > Chris
          >
        • c.ruzer
          Chris, by how much does the pink board deform under various loads? How soft or squmbly (tech term) is it? It doesn t have to be as stiff, tough, and etc as
          Message 4 of 20 , Jan 4, 2011
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            Chris, by how much does the pink board deform under various loads? How soft or squmbly (tech term) is it? It doesn't have to be as stiff, tough, and etc as plywood. For an instant boat you may need to add some panel curvature by adding some arc to bulkheads or frames, or just make the foam layer thicker. Use less expensive polyester resin and glass for same to lower the cost. Probably overall similar/lower cost than a plywood boat from better stuff. I don't think you'd need any complicated set up for an instant boat (molds, plugs, etc). Cut the foam panels, hot glue tack them together, round angles off and fillet as the spirit moves, apply glass.

            Thinks.. asks.. doesn't Dave Gray knock PDRs (family Brickoboatean) out of foam sandwich to good effect?

            Another example, not instant though a Bolger: DOLPHIN #259, surf pulling boat for 4 oars, load waterline from 660lb to 1200lb, 17lb lead ballast in the sailing version centreboard, keel, thwarts, breasthooks, knees, posts, hefty bouyancy FOAM SUPPORT to LARGE stern and fore sheets, 21" amidships keel to gunwhale height, 18'x 4' overall, 0.5" strip plank build, ought to weigh what do you think empty? 250 to 300lbs?

            What's that? Heavier?

            Well then, try only 100lb got out of 3/8" foam sandwich:

            http://groups.yahoo.com/group/bolger5/photos/album/837076775/pic/list

            http://groups.yahoo.com/group/bolger/message/48541





            --- In bolger@yahoogroups.com, "Christopher C. Wetherill" <wetherillc@...> wrote:
            >
            > All this discussion has brought to mind an old question I have been
            > pondering. Has anyone built an Instant Boat from 1/2" pink board with
            > fiberglass on both sides? Issues I have been considering
            > 1) easier to work than plywood
            > 2) slightly less costly than plywood
            > 3) not as stiff
            > 4) possibly lighter than plywood.
            >
            > I suspect that the need to glass both sides will result in no savings of
            > cost or weight.
            >
            > Chris
            >
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