The hatch will be an issue for sure, however - if he gets lucky initially and the hatch is on the windward side for awhile its failure will be delayed. He may not sink initially for a hatch failure, but it would be catastrophic.

Ironically, all the foam that he may be counting on to save his butt may be part of the reason the hatch is under water in the first place. All that stuff has done is add weight to the structure without adding any flotation. If not part of the original design (if there really was one) it could account for it floating lower on it lines.