Please tell me if I'm going at this right. I bought 4'x6' worth of 3/4" Baltek balsa core material. It is connected by a webbed mesh on one side. I planned on buying some glass mat and resin and just glassing up. I would then cut out the holes for the scoops and glass the scoops in. Then fill with 3m filler sand and gel it all.

gonna be way to heavy... get some honeycomb mat.. plasticore !!!!! never rots..and is way lighter !

Basically that's all there is to it, although if you want any shape but flat, it will take some more doing. Also plan out the edges and figure out how to detail it to fit what you are doing. I would also glass in some stronger wood instead of the balsa in way of hinges and other hoist/ram fittings. If you want to be able to walk on it, you should do some basic engineering of the laminate, and/or provide some spars that you can just look up from the wood tables for strength. Pm me if you want any help with that.

3/4" is prefect for what you are doing. You can also build a temporary mold from a cheap sheet of Formica or something like that. Makes it way easier to finish, if your careful enough you can build an almost finished part right from the mold. On hatch lids I use a simple schedule of gel/mat/1708/1708/core/1708/1708. You can also use a couple strips of core as stiffening ribs on the inside. I assume your lid is a simple flat piece that sits on a 3/4" ledge around the bilge opening and does not need a flange around the perimeter.

Not to steal you thread but Will that coozboard work for hatches.JOHN SR

yep if you only need flat panel and i would still lay it up the same way but would have to bag it to ensure a void free surface.

Here's mine using melamine as a form to duplicate the missing engine hatch. I used the "male mold method" it's the oposite of poping a part from a mold......It came out great for a one off part.

Thanks all. The hatch is basically flat, there is a slight crown to it that I will try to emulate.
I will post pics as I go along.