Plywood bulkhead reinforcement with infusion and foam doubler?

I have a vintage fiberglass deep vee power boat- 40 years old- a 25 footer with 8 foot beam with single I/O. The plywood bulkheads are old and haven't been treated well. I would like to piecemeal reinforce or replace them. They are mostly 1" ply , tabbed in with modest amounts of heavy woven roving.

I am considering drying them, sealing them with neat vinylester epoxy, then vacuum bagging a high density foam sandwich core over them, perhaps using infusion to keep it neat. Then I may leave the plywood, or I may tear it out. I need to tab the sandwich into the hull and deck first.

I have to imagine this won't be an original approach? But new to me. I will practice with some divinycel on fuel tank hatches first, to get my infusion technique right.

I would prefer to use vinylester-epoxy, not the normal Bisphenol A epoxy. I can't imagine that's a dealbreaker? :?:

 

Drying wet, possibly damaged plywood takes a lot of time. It's usually more cost effective to replace it. I see no advantage to applying a core of any type. The problems are; the tabbing, likely the resin system (polyester) and the resulting damage from the crappy work performed by the manufacture.

I guess what I'm saying is why make more work for yourself, access and address the issues and move onto the next set of issues. If the plywood is salvageable, hack the lousy tabbing off it and apply a more prudent tabbing schedule. If the plywood needs repair, scab in some more, then tab appropriately. Lastly is wholesale replacement, if the plywood warrants it.

 

The plywood is trapped below deck, supporting part of the deck and helping hold the hull shape on the trailer. So I think cutting it out on the trailer can risk deforming the hull and then locking it in place. The ply isn't mush, but it isn't amazing- it is 40 years old. And it is plywood. In the bilge, in an otherwise glass boat. I see no reason for plywood in a bilge when everything else is glass.

I may build a 1/2" H80 piece full size, jigsaw cut it to get in the bilge, bond it to the ply, holding in place with screws. Then pull screws, put another layer in with seams in different locations, pull screws, then glass over that. Then make the hull joint fillet with one of the products Ad Hoc mentioned (I think) like Crestomer 1152. The glass tab would be one sided unless/until I removed the plywood, when I could do the other.