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Marine plywood is not rot resistant. It is a higher grade of plywood that is supposed to have no internal voids. And the exterior plies should be knot free. It also of course made with waterproof glue. Generally it’s made wood that is lighter as well.
For something like the bottom of hatch any ACX (X meaning exterior which has waterproof glue) plywood will be just as effective. For considerably less $$$
The key being that it is well encapsulated with expoxy/resin. Which obviously Yamaha failed at.