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Is epoxy absolutely necessary to waterproof a plywood boat and how thick should I make the bottom,flat part?

I plan on building a plywood boat and will buy plans.But was wondering about the thickness of the plywood to use and can I just use regular plywood (exterior use type ) instead of marine plywood.And do I have to steam the plywood for bending into shape for the sides as the bottom will be flat?I plan to incorporate the ribs into the seats to cut down on the amount of plywood I use.I plan to use a thicker wood , probably planks or solid pieces of timber for the transom.Also I don't know if it is worth it to use epoxy for waterproofing the boat.I do plan now to use galvanized,stainless steel, bronze or brass screws.

Public Comments

1. First, definitely use marine grade plywood! there are some grades of exterior (used for outdoor signs) that are acceptible, but you need to be cautious even of them. If you use they proper grade plywood, you won't necessarily need to epoxy everything - though it doesn't hurt to do both (but there is a weight consideration). If you build a plywood design, it will most probably be hard-chined and therefore would not need to be steamed - there might be some bending of the material, but not so much to require that. Think a lot about weight - try to keep it down. You want a strong boat, but not one that is a pain to transport and a slug to sail!
2. Whats the reason you want to build a plywood boat, Do yourself a favor if you want to build your own boat.. build it out of fiberglass or aluminum .. you can have a local sheet metal shop cut and bend the parts.. the riveting can be fun . just seal the seams before you do your riveting..And if you do it this way you wont have to be worried about rot and sealing plywood... I hope this helps you... Good Luck
3. + For years plywood boats were just coated with oil based paint. You can bend and screw the plywood to your frame(the better way is to steam it to shape). The plywood should conform if the boat is not too big and you are making a small skiff or row boat. most people use bronze screws but depending on how long you want it to last, you could use others just remember that even stainless steel and galvanized fittings will rust in ocean water or if given enough exposure. If you plan on using an engine the transom will need to be reinforced and braced(even a small outboard). After your paint dries put the boat on saw horses and fill it with water as a test for both strength and water tightness. Good Luck, as you can find used boat for pretty cheap this time of year and just improve them, or is it the challenge that you are going for. The thickness of the wood depends on your size and weight carrying requirements. Marine plywood holds up longer. Be your own judge. Is the boat disposable and for light duty. How many years do you plan on using it?