waterproof

I'm building an 11' x 4' flatbottom plywood boat with an 8' floor and 3' bow and 1' sides. I'm building it out of plywood and I need some advice on water proofing and joining the boards .

 

Use your search resource to find......stitch and glue method, look at West System, also look for information at Wooden Boat Magazine web site. The West system site is helpful in describing the things you want to know about the epoxy adhesives and coatings that is so often used in boat building.

You will almost surely want to make the sides of your boat higher than 12 inches. Fifteen inches is more realistic and more than that is specified on a lot of small boats.

 

if you are doing a low cost build with lumber yard materials, than use the construction grade polyurethane adhesive/sealant at all the joints and just screw it together. This is the stuff that comes in Caulk tubes and you use a gun to apply it, kind of peanut butter colored. It is very tough and waterproof, and not too costly. The plated or coated exterior decks screws work well for a low cost built. You use a light frame of sawn lumber at each joint, a chine log, gunwale, etc.

than paint it with six or seven layers of high gloss Latex paint, inside and out. If you store it out of the weather it should last for a number of years and will serve you well.

I would advise against using CDX plywood, AC or AA plywood (with exterior grade glue) is the best a lumber yard usually has. Or of course marine grade plywood if you want the spend the extra money to built a top quality boat that should last for many years.

Using fiberglass and epoxy over the outside, as suggested above, adds a lot of cost but will make the boat more durable. If you are going to spend that much on your boat than it would be best to use marine grade plywood. It still needs to be painted because the epoxy breaks down in the sun unless it has some UV protection.

good luck.

 

Your best bet would be to do a little reading before spending any of your money, time and effort.
There are a number of books dedicated to building simple boats of plywood -
I recommend Build the New Instant Boats (or any of the "Instant Boat " series) by Harold "Dynamite" Payson, or Jim Michalaks' Boat Building for Beginners and Beyond. All of these will have the information you seek, plus some plans for a few simple boats. You can get them online, or through your local library (though you might have to use interlibrary loan).

Good luck!

 

Sounds like too big of a project.

 

Everyone is trying to make it simple, not as complicated as it could be.
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