1/4 inch Plywood canopy roof

Discussion in 'Wooden Boat Building and Restoration' started by Bill57, May 16, 2009.

  1. Bill57
    Joined: May 2009
    Posts: 1
    Likes: 0, Points: 0, Legacy Rep: 10
    Location: Maryland

    Bill57 New Member

    I'm building a wooden canopy for a 23 ft steam launch. The basic shape of the canopy is an ellipse about 15.5 feet by 6 feet. There is a slight curve from left to right and front to back, sort of like a potato chip. The frame has a perimeter about 2.5 inches tall and made of 3 strips of 1/4 marine fir plywood epoxied together with 7 radiata pine cross pieces every 2 feet.

    I'll be using 1/4 inch plywood for the skin of the roof, but I'm not sure what type of plywood wood be best. I intitially thought of using luan with the top covered with epoxy/6oz cloth and then paint. But now I'm wondering if a better plywood ( okume ? ) and Interlux Brightsides paint on top would be easier and just as good. There will be a few seams where sheets meet that might need a strip of cloth and epoxy.

    Any opinions or advice would be greatly appreciated.

    Bill
     
  2. PAR
    Joined: Nov 2003
    Posts: 19,133
    Likes: 490, Points: 93, Legacy Rep: 3967
    Location: Eustis, FL

    PAR Yacht Designer/Builder

    Pictures will determine, if the compound curves you've described can be accommodated with plywood. You can force thin plywood to take some compound, but not a lot.

    If this is the case you'll have to diagonally plank the top. I'd recommend two layers of 1/8" might be a better choice so you can stagger the joints and have the strength necessary.

    Home improvement luan is usually very poorly made, has very thin external veneers and only 3 layers. There's also the potential for less then waterproof glues used within the panel.

    Depending on where you live in Maryland (I grew up on the eastern shore) you should be able to find a marine plywood retailer fairly easily.

    Sheathing with 6 ounce and epoxy is just a good idea and will preserve what you got.

    If the compound curve isn't too severe, then you can usually force the plywood to take this shape, though it will place a fairly high stress on the frame work holding up the canopy. More often then not when you force a piece of plywood like this you need closer beam spacing then you have, but if the curves aren't that bad, it could work.

    Again, these are just guesses until we can get a look at what you're dealing with.
     
  3. alan white
    Joined: Mar 2007
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    Location: maine

    alan white Senior Member

    You'd be best advised to use a marine plywood for lack of voids and thick enough surface plies, along with overall uniformity. However, your roof is also very well suited to cedar (or similar light wood) strip construction, which will yield a slightly thicker but likely about equal weight structure. It weould have to be glassed both top and bottom but you'll save on plywood costs and there won't be any seam issues. It would be stiffer as well.
     

  4. Capt. Mike
    Joined: Feb 2006
    Posts: 24
    Likes: 2, Points: 0, Legacy Rep: 30
    Location: St. Augustine, FL / Bahamas

    Capt. Mike Junior Member

    Consider making the frame as you described, but then use a fabric (Sunbrella) cover. You can get the curves you want by using supports with the curves you want.
     
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