Creating a foam mold for a kayak can be very simple and need not be very expensive. If you use a stack of a dozen (or so) layers of 1 inch thick plastic-foam building insulation, you can determine the hull otline by marking widths taken from a table of offsets directly on the panels, and then trim them with an inexpensive heated wire tool. While you are working on a panel, cut out the shape of your cockpit, or paddling seat, at the same time. You can start a cut in the center of a panel with a knife and then enlarge it with the hot wire cutter.

If you want a small paddling seat molded on top of your boat you just have to carve the top 4 to 6 layers of foam. If you want a large, deep cockpit which you can crawl into, you'll just be cutting out more material from the centers of a few more panels.

Stack these up, and hold them together with a light application of building adhesive. You just have to round down the soft edges to get your symmetrical shape. A piece of coarse sandpaper wrapped around a short chunk of 2x4 will do the trick in next to no time.

Then, lay glass cloth on the outside and coat it with epoxy resin. Build up two or three succesive thin coats of resin to smooth over the pattern of the fiberglass cloth's texture (hide or fill the weave) then sand lightly, paint, and paddle.

Don't worry about disolving out the plastic foam. With a sit-on-top design that interior foam simply adds some strength as a very small sacrifice in weight. With the exception of cutting out the centers of the panels for your seat, this is a process that is similar to one used for creating surfboards.

Hope this helps.

PGJ