We've found that the wooden floorboards on our boat have lasted about 20 years. They're made of 3/8" teak/holly ply. We replace them as they become delaminated or rotted from frequent immersion. Our bilge is rather small and fills easily. Some of the original 1981 pieces are still fine.We give the new ones a double or triple coat of epoxy to ensure water doesn't get in again, and then a similar number of coats of varnish to protect the epoxy from UV degradation. The teak/holly ply is pricey, but we don't think we'll be needing to replace the new floorboards any time soon.