Would like to re-read an old post

Discussion in 'Sailboats' started by sawmaster, Aug 21, 2012.

  1. sawmaster
    Joined: May 2010
    Posts: 134
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    Location: tyler,tx

    sawmaster Senior Member

    does anyone remember a post sometime back about stiffening the bottom skin of a plywood dinghy in the area of the cockpit floor by glueing thin sheets of styrofoam ? (I think there were some thin wood strips involved as well) Im looking for the best lightweight solution to reinforce a 1/4 in or thinner bottom panel for a 255 lb skipper.Ideas are welcomed.
     
  2. CutOnce

    CutOnce Previous Member

    Sawmaster:

    You might be referring to a design Eric McNichol did for my son's boat. The boat was constructed using 2" foam between two pieces of 1/4 plywood. The resulting deck is strong enough to bear the 255 pounds easily without deflection.

    I'm sure the curve of the bottom panel added some strength. Each vertical 2" styro "rib" was fixed into place with foam-friendly PL-200

    The resulting boat outlasted my son's two year use of it and still works as good as the day it was finished. A few bangs and scuffs, but it is ready to go on to the next kid who wants to learn how to sail.

    --
    CutOnce
     

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  3. sawmaster
    Joined: May 2010
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    Location: tyler,tx

    sawmaster Senior Member

    re:styrofoam reinforcement

    Thanks:think I'll try that in the cockpit area
     
  4. Petros
    Joined: Oct 2007
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    Petros Senior Member

    easiest thing would be to glue down another layer of 1/4" plywood. If you want it light weight, how about 1/4 or 1/2 in foam sheet, with an 1/8 layer of plywood over it to protect it.
     
  5. sawmaster
    Joined: May 2010
    Posts: 134
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    Location: tyler,tx

    sawmaster Senior Member

    If stiff enough,even better. I was thinking maybe 1". Whats a good source for styrofoam sheet material ?
     
  6. CutOnce

    CutOnce Previous Member

    Home Depot and Lowes sell the cheap white stuff for insulation, as well as the more expensive blue stuff. Any building center will have it.

    I used a Dozuki (Japanese hand backsaw) to cut it to fit, works a charm, but the driveway looked like a January snowfall. A little breeze and everything was back to normal.

    --
    CutOnce
     

  7. upchurchmr
    Joined: Feb 2011
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    Location: Ft. Worth, Tx, USA

    upchurchmr Senior Member

    Styrofoam is really not worth much.

    Make your self three beams and load them to see how much they bend. make the beams about 24", clamp 6" to your table. Drill a hole in the end to apply weight.

    First make a 4" wide sandwich of 1/4ply, 1/2 foam, 1/4 ply, all glued together with something that wont attack the foam. Yellow glue works, and epoxy of course.

    Then cut two pieces of 1/4 ply, don't glue them together.

    Last make a sandwich of 1/4 ply, 1/2" high x1/4" wide cedar strip (use 2 strips with a 2" separation) then 1/4" ply.

    Clamp each "beam" at the far end of the overlap, as far away as you can get from the edge. Load each beam with the same weight 1# to start, and measure the deflection at the end.

    Notice that the deflection of the foam beam is not much different from the 2 stacked, unglued pieces of ply, but the 1/4 stringers is really stiff.

    In practical use you might put foam between the stringers just to keep any water from collecting.

    Last try the same thing with 1/8 ply, 1/2 x 1/4 stringers, and 1/8 ply and check the stiffness. Especially compared to the foam.

    My conclusion is that the 2 unglued pieces of ply is just about equal to the foam beam. If you glue the 2 pieces of ply together, it will be much better than the foam.

    If you replace the styro with something good (expensive) you will have much better stiffness than the 2 glued plys.
    The Gougeons have used paper honeycomb core instead of foam with good results. Not intended to be continuously in the water.
     
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