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Marine plywood is more rot resistant than regular exterior plywood.

  • False. The difference is primarily in the quality of the inner veneers. Marine plywood does not contain the voids that always exist in exterior grade plywood.

plywood voids

Cheap plywood can be made into marine grade by coating with epoxy.

  • False. The difference between exterior grades and marine grade is structural (elimination of all voids). No amount of coating will make up for poor quality inner plies.

Adding flotation to a boat increases buoyancy.

  • False. I’m sure if people really thought about it they would know the answer to this one, but a pound of feathers is still a pound; buoyancy is decreased by one pound. Flotation only adds buoyancy when the boat is full of water.


A pontoon boat will have less draft than a flat bottom boat of the same weight and length.

  • False. I have included this one because I have had to explain it so often. If you compare a 4′ x 10′ box that weighs 100 lbs. to a 4′ x 10′ deck with two pontoons that weighs 100 lbs.; the pontoon configuration will sink lower in the water (have more draft). Buoyancy is determined by the volume of an object in the water and the weight of that object.

One can make their plywood boat stronger by adding fiberglass to the outside.

Fiberglassing my boat cropped

  • False (mostly).  In a plywood boat, the strength is in the wood. Fiberglass adds a tough surface to protect the wood from abrasion and to prevent water from seeping into the boat from poor planking junctions. It also allows the builder to get a better finish on his boat. If you want to make the boat stronger, increase planking thickness. Adding enough fiberglass to make a structural difference is both expensive and adds considerable weight. In stitch-n-glue construction, fiberglass laminates take the place of a wooden member, fastening, and glue; which is structural, but fiberglass coating of the plywood only serves the purposes described above.

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