For marine-grade plywood, should I go to a lumberyard or a boating
store (we have Boaters World and West Marine nearby)? I guess I would
get the same thickness as the current boards. Is there a special type
of epoxy to use? I presume that you mean to saturate both the cut
edges and top/bottom of new floor boards? This sounds like a lot of
work if I then have to varnish too, but maybe it will be worth it if
they last a few years. I would like to get another 4 years or so out
of the dinghy. The only other problems we have with it is that the
finish has become "chalky".