Here's something that I've read, but not actually experienced ...

Most domestic (US) marine grade plywood is fir - and it supposedly "checks" over time, so that painted surfaces will have small cracks that allow moisture in - this supposedly will not happen if the plywood is covered by epoxy/fiberglass.

Another comment is pliability - I used 4mm Okoume plywood on a kayak, but I can't imagine forming a good hull shape with regular 1/4" (about 6mm) marine plywood- my opinion is that it may not be flexible enough to bend to the hull contours that my plans called for.