Dive boat Deck Replacement - Help On how to??

[Capt Ram]

Hi Guys! I’m New to the form and to fiberglass work- I’m working on a project and would appreciate your advice!
I’m replacing a deck on my commercial Dive boat ,8x9 feet- the deck is shot it gets lots of hard use and had a 10 year life-- it was made of balsa enclosed with about 3/16 of glass on both sides- I would like to - replace it once and for all then put her back to work-
What would be the best materials/ methods to use ?
¾ marine Ply with 3 coats on the underside of Epoxy? How many layers of cloth & what weight on top side? I’m taking the 2 top outer boxes out the rest will stay so I need to brace under the area where the boxes are/were supporting the deck what kind of wood should I use? How can I make the deck smooth once I lay down the cloth/epoxy? Any advice you can give will help a lot- What kind of epoxy ? about how much is needed? Thanks in advance!

What failed on it before? (what were the mechanics of the failure - Water from a crack at an edge, delamination and collapse, puncture?) Are you limited on how thick it can be?

[Capt Ram]

Thanks Mark , it had many failures from around the hatches were worn thin from years of tanks being dropped/slid/divers/ and then holed & some screw holes that were not sealed right- to cracks at hatch edges- around the hatches were not built strong enough so flexing occurred on the flange where small cracks let water in and balsa rotted- I’m not limited on how thick it can be

[alan white]

With that much abuse expected, plywood is probably the best choice, though it's hard to tell from here whether the balsa-cored deck failed because it was balsa rather than plywood, or, as is most common, from water leaking into fastener holes.
Shocks to balsa could delaminate the core from the skin in any case, so the question is what thickness of plywood to use.
3/4" might be overkill--- depending on frame spacing and spans. A good quality marine grade plywood is inherently stronger than off-the-shelf box store plywood, and much more expensive too. It may be that 1/2" would do, but again, only if the frames are close enough to minimize flex.
However thick the balsa core was, that's going to be about what thickness the plywood should be, so long as the old deck failed due to reasons other than balsa thickness being too thin.
It might also make sense to thicken the top skin to 1/4" for better impact resistance. Rubber mats, if appropriate, would go a long way towards cushioning the deck from abuse in the future also.