Re: OT: Seeking Plywood Boat Plans [long post]

Posted by MarkB_MI on October 20, 2005 at 18:00:08 from (64.31.10.187):

In Reply to: OT: Seeking Plywood Boat Plans [long post] posted by Buzzman72 on October 20, 2005 at 07:42:16:

There are countless different ways to build a boat. I built a lapstrake plywood canoe, which is a good-looking boat but it took a lot of work. The way your dad's boat is built is probably the simplest: just bend pieces of plywood into the shape of a boat.

There are tricks to taking measurements off of a boat. I've seen it described in old WoodenBoat articles; I'm sure some of the boatbuilding books describe it as well. Suffice it to say you can't do it with just a tape measure. You have to measure the "offsets", which describe the curvature of the boat.

If you really like the size and shape of your dad's boat, you might be able to use it as a mold. You could wrap plywood around it, temporarily fasten each piece to the old boat, trim it to fit and remove it. Once you had each piece cut to size, you could then assemble the new hull over the old boat, then pull the new hull off, install the thwarts, etc and you'd have a boat just like dad's, just a little bigger.

A good book on plywood boats is H. H. Payson's "Instant Boats". See the link below for more information.

Some suggestions:

1. Use marine plywood. Regular exterior grade plywood has voids where water can collect. You can get away with exterior grade plywood if you sheath it in fiberglass, but then it would just be another (heavy) fiberglass boat. You can get marine grade fir plywood, but a better product is okume (african mahogany) marine plywood imported from Europe. It comes in millimeter thicknesses; my canoe is made from 4 mm (3/16") Okume. (There are several different brands, you can find them in WoodenBoat).

2. Although your dad used brass screws, you should really use silicon bronze. These are available from Jamestown Distributors (www.jamestowndistributors.com). You can probably buy bronze screws from Jamestown for less than what brass screws will cost at the hardware store. Jamestown also carries a variety of bronze boat nails and other products, be sure and get their catalog.

3. Presumably you're going to use some kind of adhesive. WEST System epoxy is very good, but maybe not the best choice for plywood-and-screw construction. A lot of boatbuilders use 3M 5200 polyurethane marine sealant. It does a great job of filling gaps and is quite flexible. Be sure and clean it up with acetone before it sets up, because once it sticks to something it's there forever. 5200 and WEST are both sold by Jamestown, plus a bunch of other adhesives.

One more thing: If you want the lightest, best-looking boat you can own, glued lapstrake plywood is the way to go. (My 11'6" canoe weighs 35 lbs.) The best book on this type of boat construction is "Ultralight Boatbuilding", by Thomas J. Hill. ISBN 0-87742-244-3

Good luck!

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