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Hi Scubadog,
Thanks for the compliment. When I re-did the deck panels in my boat, I used only two layers. The material that I removed was in many places rotten but it was clear that the original layup was two layers of ply with a layer of chopped strand glass between them. I chose to use birch plywood made from WBP glues. This is effectively marine grade. I used two layers of 1/2" milled down such that the overall buildup including the fibreglass would be just about 15/16". I also let in 1/2" x 4" aluminum flat bar in strategic areas so that I could drill and tap the fasteners for the console, leaning post, T top etc... The result is, in my opinion, very stiff and better than the factory. Good luck with your project.
Hi SD,
Measure twice and build a jig to guide the hole saw. There is a clear path through but there isn't much extra room to play with. Good luck.