The Rot Doctor


Subject: Fiberglass boat stringer replacement
Date: Tue, 09 Feb 1999

Dr. Rot,

I have an old 16' MFG bowrider with the deck already removed and the stringers about to be removed. They're 3/4" plywood, of all things, about 10" high and almost no substantial wood left. The question is what to replace them with. Whatever I use, it'll be saturated with cpes, obviously.

If this were a favorite boat that I planned to keep, I'd use white oak or mahogany, but I only want to make it sea-worthy and sell it. I'm a conscientious sort, and want to do a good job, but not quite as good as oak! I doubt if they need that much strength anyway, since plywood worked before it rotted out.

If I use plywood, will the cpes be able to penetrate the inner plies from the edges? Should I use 1x fir (not cheap either!) instead? I guess I'm leaning toward ply, if you can tell me cpes will reasonably protect it.

When I replace the deck, should I use epoxy or 5200 between deck & stringers? Can't effectively screw into edge of plywood stringer, so how to fasten?

Thanks in advance for your advice!



I'd use exterior grade plywood and give it a good coating of the CPES, which will penetrate plywood edges very well indeed. Plywood is plenty strong for this application. Cut the ply to the exact installation dimensions and then get an old brush and some CPES an just start dabbing the stuff on the edges. Allow the wood to take all it will accept. Give a coat or two to the flat sides too. Give it about three days for the carrier solvents to evaporate away and the epoxy to cure and then install. If you drill holes or make cuts in the wood during installation, have a little CPES handy to apply to the drilled or cut locations.

You could get fancy and use fir pieces or something even more expensive, but I don't think it would do a thing for you that the ply won't. Your instincts on this are absolutely correct. Anyway, IMHO the ply after being CPES-treated will last as long as the fir or oak or whatever.

For attaching the deck to the stringers the 5200 should work, as long as you remember that it remains a bit flexible. This shouldn't make a difference, but then I'm not looking at the project so am cautious about making absolute statements. You could use an epoxy, such as our Tropical Hardwood Epoxy Adhesive, but it is about twice as expensive as 5200. Probably would hold a little better buy on a deck this is probably not an issue.

And yes, the 5200 will stick very nicely to wood that has been treated with CPES.

Come on back if you have more questions.