I'm in the process of repairing an old outboard powerboat. The thing is 30 years old. It was built with fir stringers covered with glass/polyester resin. The transom was mulch but the stringers were like new. This, in spite of incredibly sloppy workmanship.

I'm rebuilding with marine ply and epoxy and expecting the thing should outlast me.

btw. I've also discovered that the folks on the powerboat forums are, by and large, far more friendly, helpful and generally enthusiastic than most of the knuckleheads on the "old" catsailor forum. Kind of sad that after 20 years of sailing catamarans I'm finding myself gravitating towards the powerboat crowd.