Bending plywood panels

Discussion in 'Fiberglass and Composite Boat Building' started by Brands01, Jan 29, 2007.

  1. northerncat
    Joined: Jan 2007
    Posts: 170
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    Location: australia

    northerncat Senior Member

    i have seen the use of a biscuit join between 2 using a sheet sized biscuit between 2 sheets of ply with a piece of glass down both sides, very neat and when tested to destruction as strong as a butt join and stronger than a scarf, biscuit was 50mm and went 25 mm into each sheet
    sean
     
  2. Raggi_Thor
    Joined: Jan 2004
    Posts: 2,457
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    Location: Trondheim, NORWAY

    Raggi_Thor Nav.arch/Designer/Builder

    It's indeed a good idea to scarf or join the plywood before you bend it!
    You will save a lot of work if you can manage to bend the larger panels smoothly.
     
  3. boatbuilder.org
    Joined: Jan 2005
    Posts: 54
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    Location: Olympia Washington

    boatbuilder.org Junior Member

    Theoretically yes it should work, but I theory and practice are not always on the same page. At the very end of the hull I put it a 2x6 vertical that ties the bottom panels to the chine harpin and the chine harpin the the sheer harpin. If you take a 3" wide scrap of plywood and put packaging tape on it you can screw through through the scrap / panel ends and into the vertical piece to get it all to suck up tight The shiny packaging tape wont stick to epoxy so you can unscrew and knock it off the next day. On additional layers I stagger the joints and just use the hull to screw the scrap and panel to. There are a lot of holes in stern afterward, but they will fill. Here is another link to my other website where I bent plywood around a stern that has sharper curves than the plywood could make without breaking http://www.boatbuilder.org/godzillishull.htm
    ---Joel---
     
  4. boatbuilder.org
    Joined: Jan 2005
    Posts: 54
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    Location: Olympia Washington

    boatbuilder.org Junior Member

    If your panels are lofted and cut perfectly and assuming the cad numbers are perfect yes it could work, but the computer generated its numbers in a perfect world and there are variables it can't/won't account for.
    I always scarf the panels. I do glass the butt joints in the stern of something like the Sockeye but that is on the inside after the panels are all tabbed in place. I would not do it where there is only one layer of 1/4" plywood cold molded over it, but on a boat like the Sockeye we add 3 to 4 layers of 1/4" plywood over the first panel. I, personally, still would not do it even on the Sockeye but don't I see it as a structural issue. For me scarfing it easier. I even scarf plywood for cabin roofs and wide fore decks over 8' so I can lay the sheets in one piece from side to side.
    ---Joel---
     

  5. Brands01
    Joined: Nov 2006
    Posts: 102
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    Location: Sydney

    Brands01 Senior Member

    Yes, I like the idea of the frameing in the stern to get all the panels to suck up and sit properly. And your pictures of the Godzilli are also very informative - I think that's the way we'll go.
     
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