Trimaran sailors..........

[UNCIVILIZED]

Definietly build breakwaters around 3 sides of the hatch. All sides but aft. And you'll likely want to include a few side drain holes through their bases.

Also, if you're feeling paranoid, you can incorporate attachments for canvas storm covers into the breakwaters. Some folks use boltrope attachment systems for them, again, on 3 sides of the hatch. Along with cords built into the covers so that they can be well cinched down.

You'll find some good DIY resources for this stuff via kayak builders, & those that sell plans & kits. Since they absolutely have to keep their gear dry, despite continuous green water over the decks at times. Plus they have systems for remote control bilge pumps. Both electric, & human powered.
Ah, & they stock gasket material, & hatch dogs as well.

[paxfish]

Once you've built it - get these guys to test it (Schionning)

https://www.youtube.com/watch?v=6iUNkUJ_GNI

[w32honu]

As mentioned...... the hatches are a work in progress. The covers will fit snugly over the top of both combings with gaskets.

[w32honu]

Very kewl video by the way...........

We enjoyed that one.