Lightweight engine Hatch. Nidacore, Carbon core, or ????
I am making a new hatch for my Scarab 33 AVS and want to lose weight. The old one is about 150 lbs. I do not need foam I just want to walk on it, and have it LIGHT weight. I was going to go coosa but I think there are ligther materials . Any thoughts.

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I build all my Parasail boat flight decks, hatches, floors, ect using Nida Core or equivalent. When done properly, it's solid as concrete and extremely lighweight. Good luck.

Ok looks like I am using Nida core 1" with glass and bracing ribs.

Is the hatch flat or slightly crowned?

Forgive for jumping in, but let's just say it's slightly crowned then what?

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I'd be very curious to see the process of using the nidacore if you don't mind showing that? Also could it be used for structural things like seats and such? I need to rebuild my backseat and hatch this winter to accommodate my new motor and I never knew this stuff existed until you started this thread so some progress/process pics would be awesome!!

Thanks in advance for any help!!

Same materials , just was going to discuss easy methods to build either style hatch.

Whatever they call themselves any modern composite foam core will suffice . The only REAL weight saving comes from not using a wood coring material. You can pick up a 4'x6' sheet of foam core easily with one hand but try it with the same sized piece of plywood .
The fact is you're still going to use very similar amounts of glass and resin in the construction especially when you factor in the required support crossmembers .
I've done an engine hatch using balsa core and gas tank and lazarette hatches using foam cores and I can say that balsa does start out very light but it can absorb a lot of resin in the process. Not quite as much though for the foams .
Also , with foam cores you have to be a little more mindful of through bolting hardware .