Foredeck hatches

I’ve got some hatches that I’m going to install in the forward cabin roof for light and ventilation.
“I’ve never met a hatch that didn’t leak” is echoing in my head, so I want to do this right the first time!
The deck is 1/2” plywood with 1708 and gelcoat on the outside, and painted inside.
Should I build raised frames on the roof to divert water away from the hatches, or is correctly installing with quality sealant enough?

 

Raised frames sounds more safe solution .
How to design hatches that don't stick out and are tight when building a sandwich hull.

 

What type of hatches are you installing? If they are flush hatches the raised frames would defeat the purpose of the design.

 

They’re raised not flush, and have a bolting flange that sits on top.
Can’t think of the brand right now.

 

Another reason you may want to raise it, is to create a flat surface on a cambered deck. I had t make a hardwood frame to fit the deck before bolting down the hatch and frame and sealant. Gebo hatch, never leaked a drop. The hardness of the rubber seals seems to be a key factor on longevity/leaking issues.

 

You’re quite right re the camber. It is slight, but the aluminum frames are very flat, so the sealant would have to be thicker at the ends, and the fasteners would be fighting to straighten out that part of the deck or bend the frame, encouraging leaks.
I’ve got some coosa scraps, guess it’s time to get busy!

 

I just recalled it was a Bomar hatch, not Gebo.
If its a sailing boat, just be mindful of rope traps with your plinth or hatch type, some hatch lids have a rather wide gap, rather than flush, something a flogging sails sheet could get caught in and in one case, pop the hatch cover, usually at the worst possible time.