: ...I don't see how this could happen. I cannot envision a scenario where I
: would be trying to do a re-entry (that's what you're talking about,
: correct?) with a hatch open.

(not the same as in water, but if the rigid hinge attachm't is permanent, while on shore, one could easily step or fall on it and just destroy the mounting.)

So try a flexible hinge. Conceptually the same as if one side of the hatch bungees were multiply attached and the other free. One bungee set attached on one side, the other side set just hooks on. Hatch swings open, but approx held in place. If the deck is fairly flat, I would try to hinge at the front for safety purposes(waves etc.), but most situations would surely call for a side setup.

If your hatch sides are straight(not always true), I wonder about the possibility of gluing or attaching neoprene on the u/s of the deck and the u/s of the adjacent hatch. In essence one of the 'four' gasket sides is a hinge. The deck lip maybe should be undercut a bit to form a location for mechanical attachm't.

Another possibility is if using my good buddy silicone (but can use other and solid mat'ls), by relieving the hatch edge and allowing the upper seal to flow in (or relieve and use solid pins or wd etc.) , you can get a positive latch. Like small notches or lips fitting under a slight over hang or hole. Like most hatch systems have the flange system down a further 1/4 to 1/8 in below the u/s of the deck for the gasket thickness, so why not use this dimension for hinging or positive keying as well??

-mick