I like this idea, you are still constrained somewhat by the flatness of the sheets, but it's your boat design. I doubt anyone has done it before just because most boats have more curves. Still it sounds like an easy way to get a mold. Might want to think through how you are going to smooth the insides, mat leaves a pretty rough surface, but bondo could fill it I suppose. You might be able to get away with using mat for the tape on the mold since it is only a mold. A friend here made a mold for a hard top on a cobra, his final coat on the mold was a 2 part epoxy paint.... (cheap and smooth), enough coats could hide a lot of tiny defects. And it worked pretty well, as he now sells the tops to people who build cars

Also since it is a mold, I would reinforce the outside of the mold heavily, many of the molds I have seen/used are 1/4" or more thick of mat with reinforcing ribs glassed in too. Warping, even a little would be very bad. Even though you only want a few boats, it is suprising how well a boat sticks to even a very good mold. Wax and PVA help a lot here. There must be some moldmeisters lurking out there with some more ideas.

Bart

: hey I'v been thinking about this... and I'v decided to make use of the
: masonite without having to put it in the water. I am simply going to use
: it for a box to make a mold in. I can make a S&G kayak out of masonite
: then use the inside as a female mold. "I'm not putting the 2 halfs
: together" I can use foam and such to shape the boat to my likeing on
: the inside then put plastic or a layer of fibreglass matt down to make the
: thing a "mold" I'm only popping 2 or 3 boats out of it so I
: don't need anything high tech.

: Has this been done before?

: more details on the bottom of my boatbuilding page