What kind of boat? I have use good quality 3/4 in ply in the past as well as 2x4 or cut my own stringers out of 2x6 and sealed everything before installing.
Might want to post this in the restoration section.
great thing about the best DIY restoration forum on the planet
the answers to 95% of the questions you could have are in the stickies
start reading the links in the restoration forum. https://forums.iboats.com/forum/boa...r/295740-how-to-s-and-other-great-information
specifically link 14 and 18
any exterior grade premium plywood would be fine.
BTW, post pics of your project. most likely you didnt grind enough for the new resin and glass (most do not)
Marine plywood IS the best but...If you use a good quality ext. grade plywood, with Polyester Laminating Resin, CSM, and Biaxial Fabric. and then care and maintain the boat in a responsible manner, She'll last for multiple decades. Factory boats don't have the best quality of laminations but following the advice here on the forum Your's will be Better than Factory. I use plywood for everything, Stringers, Transoms, Motor Mounts Side panels, Seat bases, EVERYTHING.
I thought this would be quicker lol. I hope i have enough grinding done. This is a lot of work. Harder than I thought. Thanks for the response.