Marine plywood for frames

Discussion in 'Wooden Boat Building and Restoration' started by wudenbote, Sep 14, 2008.

  1. wudenbote
    Joined: Aug 2008
    Posts: 31
    Likes: 0, Points: 0, Legacy Rep: 10
    Location: Middleville Mi

    wudenbote Junior Member

    Hi again everyone! A thought just occured to me . (probably not an original one) Has anyone used marine grade plywood for frames? It would seem that you could cut out your frames from 3/4" marine ply and epoxy 2 of them together to make 1 1/2" thick frames. The advantage I would think, would be no joint at the chine. It could be a one piece frame. I realize that the edge of plywood probably won't hold screws well, but what if you simply assemble the hull with just epoxy or epoxy plus silicon bronze through bolts? Some thoughts on this would be much appreciated as tomorrow I go the wood store to make my first purchases.
     
  2. PAR
    Joined: Nov 2003
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    Location: Eustis, FL

    PAR Yacht Designer/Builder

    Plywood frames can be used, but it should be engineered into the scantlings. This is because plywood isn't as strong longitudinally as solid lumber and it doesn't hold fasteners on the end grain worth a damn. In short, if you need 1.5" sided frame stock, plywood will be in the neighborhood of 2/3's as strong as solid stock. If you increase the sided dimension of the plywood frame to accommodate the lose in strength, then you have frames that are much heavier then solid stock, that still don't hold planking fasteners.

    The only way plywood makes much engineering sense, is if you incorporate it into a load bearing panels, such as taped seam designs do. The other way is to make plywood ring frames in concert with a longitudinal stiffener, framing system or use the plywood as longitudinal frames, bonded to the hull shell.

    Use solid stock with plywood gussets at the chine. You'll have light, strong frames with stable plywood gussets at the chine. These will hold fasteners and will not be excessively heavy for their strength.
     
  3. BHOFM
    Joined: Jun 2008
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    Location: usa

    BHOFM Senior Member


  4. PAR
    Joined: Nov 2003
    Posts: 19,133
    Likes: 476, Points: 93, Legacy Rep: 3967
    Location: Eustis, FL

    PAR Yacht Designer/Builder

    BHOFM, your 1/4" plywood, surrounded with 1 by stock Is a web frame and a fairly common technique, especially in metal boats. The engineering principle works in wood too.
     
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