I am redoing a 1973 Fiberform Malibu jet boat. This boat has a 1/4 inch layer of plywood under the stringers. It appears the plywood was tabbed to the hull, then the stringers were tabbed to the plywood. On top of the stringers, a plywood deck was attached and tabbed to the side of the hull. This created two decks that the seats mount to. In the center was a recessed plywood deck with open bilge beneath. The whole assembly was then coated with fiberglass and covered with carpet. The stringers and all the plywood were wet or rotten. Originally, I was going to replace the plywood and reconstruct it how the factory made it. I talked to a local boat shop about it and they said they would leave the plywood out and add CSM/Roving to reinforce the hull if necessary. This seems like it would be easier than gluing plywood down and would not rot in the future. The cost is about a wash either way. Is there strength concerns that could arise from leaving the plywood out? It seems that the foam would provide plenty of strength and render the plywood unnecessary. Does the plywood transmit the load on the hull to the stringers? Does the plywood act as a giant bedding compound? I am unfamiliar with this type of construction. Hopefully, someone can help me out. The previous owner said the boats top speed was around 65 mph, so I don't want to weaken the structure. Here are a couple of pictures. The red outline is where the plywood sits below the stringer. Thanks for any help.

Believe it or not, this is pretty much exactly like the factory did them....

As long as everything is laminated properly it will be plenty strong, just always thought this was a strange approach... Then again, odd never meant wrong...

GT

I've done it a few ways. one way was to lay the stringer onto wet glass and put as much weight on it. the other way i've done it is to use a mixture of cabosil and resin and mix to a peanut butter consistency, lay the stringers down on that.