urethane foam in stringers

[fishweed]

Has anyone got a site were I can buy injectable urethane foam to replace the wood in my stringers?

[JR-Shine]

If the wood is there to give stiffness, then foam will not do you any good. Four foam just takes up space, its not structural.

[fishweed]

I am sorry I am not up on what Flour foam is? is it the same as a closed cell urethane?

[fishweed]

Or do you mean pour foam?

[JR-Shine]

sorry, yes, POUR foam

[fishweed]

Jr.. I do appreciate the advise, it just I know the stringers are ok because none are cracked, my plan was to replace with wood or epoxy any I can access, but some are not accessable, I have glassed boats and cars before, I am mainly mechanical,, the way the stringers are made with wood and glassing over them without vents seems to be a bad design, you are right about leaving them alone, all I have done is drill holes to let out the moisture, but I have to fix the engine and the area the mast support goes on, thanks

[JR-Shine]

OK, I got it now. Engine mounts and mast steps are another matter, you need compression strength and filling in the rotten out wood will thickend epoxy will help.

I was thinking you were trying to restore the stiffness of the stringers by replacing the wood core with a pour foam core.

Wood cored stringers are very good, but MUST be maintained - no unsealed holes.

[jimslade]

You can fill the stringers with foam but you will need to use more layers of glass to make the stringers the structural part they were meant to be.

[Toot]

Filling in hollow stringers with foam will not be productive. A structure will always flex a little bit. The key to a cored structure is the bond between the core and the glass. Only because those two things are bonded together do you get the strength qualities of a cored structure.

When you inject foam into an open space, you have shockingly little bond. Because the fiberglass is already cured, the only bond strength is provided by the adhesive properties of the expandable foam- and that's not very much AT ALL. Well, it is alright from a basic "functional" point of view, like if you want it to simply stick and stay under its own weight. But if you want actual structural strength- the ability to hold more than its own weight, then you're going to be disappointed. You need to use something designed for bonding. Like a epoxy/poly/vinyl/etc resin.

Adding more fiberglass on top of a bad core still won't create a properly cored structure because you still lack the bond between the inner core and the initial layers of fiberglass.

If the fiberglass is in tact, the best thing to do is to use a slurry mixture, with epoxy or other resin, which will actually BOND to the layers of glass. To do this, drill a small hole into the air pocket, insert a syringe filled with slurry or resin, and squirt it in there until it's completely full.

[jimslade]

There are many builders that use hollow stringers, but you must build up the stringer thickness for strength.

[fishweed]

I have made up my mind to inject an epoxy into the stringers first, a penetrating type, and then an epoxy with fillers and chopped glass, the boat is 36 ft, four stringers run to the bow, they are approx. 32 ft each, the glass on the stringers now is more than a 1/4 inch thick, I realize this will be expensive, all the other options I have looked into such as foam were to save money, but I know the best is with epoxy, I just need to find a supplier where I can get the stuff cheap