Is normal plywood ok for a cheap DIY boat if water sealed numerous times?

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  • 4 weeks ago

    Marine plywood is rated for moisture environments and is often used for making boats. Normal - home depot stuff - NOT SO MUCH. I suppose if you make a boat and dunk it several times in thick polyurethane...it wouldn't be awful. Why risk the problems though? Start with what you should be using.

  • 2 months ago

    I am from the school of thought that marine plywood is overrated. If we are talking about a jon boat here-go ahead and do it out of exterior grade plywood. The glue is essentially the same. 

    I once built a centerboard for a sailboat out of a former garage door. As far as I know it is still going ten years later. Recycled plywood can actually be a good choice. This is because A. The old growth timber it was cut from may have a tighter grain than new plywood cut from fast growing plantations, and B. Back in the day plywood makers knew that everything from boats to airplanes would be made from their product, so they took great care to have their product accepted in the market. The plywood marketing association gave away free plans for the Thunderbird sailboat starting in 1958. Some original Thunderbirds are still sailing today. 

    No, your exterior grade plywood will not delaminate as soon as it hits the water. Just fill any void you find with epoxy.  If you plan to build a seagoing boat you should be using marine plywood just so it is insurable! You do not need all this sealing. If we are talking a jon boat, etc. here; tape the seams with an automotive fibreglass kit. The water does not care if your fibreglass comes from a hardware store or a yacht chandler, but a hardware store will sell you mat, resin and catalyst for 25 bucks or so.  If you are going to be grounding the boat, throw some fibreglass mat on the bottom. 

    If you are the same person who asked about the wisdom of their own design, I suggest you find a boat plan from a pro that uses two or three sheets of plywood. With CAD a pro N.A. can use every square inch of plywood. You do not need the 2X4s, you can build a good boat with just the plywood+an auto body fibreglass kit. Just use marine screws because anything that will rust will expand and lose strength. 

    Seriously-if you know of an old house that is being torn down and has dry plywood from the sixties or seventies-grab it. Pull out or drill out every old fastener and put epoxy in the holes. You can build a perfectly good boat out of it. With plywood-they do not make it like they used to do. I thought the centreboard I built out of old plywood would get me through the season. It turned out to be better than the original centreboard. If the garage of the old house has cans of now forbidden lead paint, that is good too. Just wear a mask when you use it. 

  • 2 months ago

    I built a Jim Brown 31 foot trimaran back in the 70's.   West system epoxy works great.

  • Anonymous
    2 months ago

    The reason you use the more expensive marine ply is the glue is waterproof.

    If you use ordinary ply it will not last five minutes in the water however much paint and/or varnish you use.

    All you will have after an incredibly short time is a pile of soggy boards and no boat.

    The person who claims that there are boats that have lasted with ordinary does not know what they are talking about.

    To make a boat that will keep watertight and together is why marine ply was invented.

    What you need to do is to place a section of ordinary ply and a section of marine ply into the water after coating in one coat of varnish and see which one lasts the longest,

    Both plys are reasonable quality as it's the glue used that makes the difference.

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  • fuzzy
    Lv 6
    2 months ago

    Many MANY boats have been built with non marine ply. Quite a few of them are still around.

    Some points to ponder:-

    1/ not all "marine ply" is actually marine ply - lots of stuff misbranded

    2/ most ply these days uses the same adhesive as proper marine ply

        (if in doubt boil a small piece of the ply for an hour - if it doesn't delaminate by then it's A bond & the glue wont fail in the water)

    3/ The main difference between exterior & marine ply is the quality of the plys. 

  • Anonymous
    2 months ago

    Lol, no! 

    Not if you intend to put the plywood in the water!

  • Anonymous
    2 months ago

    If you don't need to get many uses out of it, sure.

  • CB
    Lv 7
    2 months ago

    Why would you spend the time to build a boat and then cheap-out on essential materials - marine plywood - no worries, any breach in the seal (and good sealing agents are expensive) like a screw hole, rub spot overtime will compromise regular plywood. 

  • 2 months ago

    Yes but make sure it's sealed properly.  In addition to securing the joints with screws use 3M 5200.  Then several coats of paint.

  • Anonymous
    2 months ago

    For what the FlexSeal will cost you could get marine plywood.  NO:  regular plywood will still fail and you'll be swimming.

    Even the finest wooden boats depend upon the dry wood absorbing a bit of water so it swells and makes the final seal.  When your ordinary plywood gets wet, the glue will liquify and the wood will delaminate.

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