Stringer repair...

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stmbtwle

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I'm having to replace about 8' of a couple of my stringers... Formerly the stringers were made of 2 layers of 3/4" plywood, which after nearly 40 years have turned to mush... We've removed the rotten plywood and the encapsulating fiberglass appears to be sound.

Present options are to replace the old plywood with 2x8 pine boards, bed them in high density foam and glass them in. OR simply fill the now-hollow stringers with foam and glass them over.

any suggestions, tips???
 
Marine plywood or white oak. I am told that using heartwood is best as it is rot resistant. Stringers are there for strength. Filling with foam will not. All you would be doing is filling a void.
 
Why leave the old fg? I would be concerned that it is dirty and weakened. grinding it all down to clean hull and rebuilding would be my idea. Sistering the new to the remaining old rather than just a butt is probably a good idea too.
 
Talked to the local glass shop and they didn't have any problem with me keeping the old fiberglass as long as it was sound. It appears to be as the stringers have been essentially hollow for years, and the only failure in the glass was a bad joint where the roving was butted instead of lapped (factory job) and the wood underneath it rotted out. That will be corrected. Everything else is solid. Cutting it all out and starting over will add a LOT of extra work and yes cost and time ARE a factor.

I think I'll stick with hard yellow pine (sealed of course) instead of plywood as IMO it's more rot resistant and stronger than plywood.

"Runny putty" (thickened resin) to bed the timbers in has been recommended as opposed to foam. The argument was I'll have a lot more working time. It makes sense as I know foam kicks off FAST. It'll be heavier but that's not an issue. Is anyone familiar with the stuff (runny putty)???

Agree that just filling the stringers with foam wouldn't add any strength. I know some boats are built that way but this one wasn't, so the glass layup isn't likely as strong.

Aside from ripping out the old (soggy) plywood, nothing has been done, so opinions/suggestions are still welcome.
 
Hi Hogan thanks for the link, I was looking for that a while back. However after due consideration I decided to go ahead with hard pine... It's darned strong and will probably last longer than the rest of the 40-year old boat. So far the stringers are cut and fitted, we have some final grinding/prep work and then they get glassed in. My guess the repair will be stronger than the original construction. DEFINITELY the glass work will be better!

Thanks though for the link!
 
Willie
I too am cutting in new stringers on an I/O. Are you tying the stringers directly into the transom, or is there a gap between the end of each stringer and the transom.

My Larson had about 3/4" foam between them from the factory... I could make this stronger by butting them directly to each other but don't want to overlook some other critical design reason (ie., vibration)
Don
 
My stringers are in the bow. It's an inboard and any water tends to run forward, so that's what rotted.

Don't know if this is correct but I removed the wood as far forward and aft as I could leaving the fiberglass. New stringers are cut and fitted and will be installed next week, bedded in resin and glassed in with extra fiberglass where the butt joints are. A scarf joint (or all new stringers) would be better but it simply wasn't possible without cutting up and rebuilding the whole boat. One has to draw a line somewhere.

Judging from the way my boat was put together I'd GUESS the foam is there to fill in a gap left during construction. It's hard to get a perfect fit and there are always gaps somewhere that have to be filled in.
 
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