Re: 1988 sea ray seville stringer replacement
The number and size or stringers will depend on a number of things; the design of the hull and the size and location of chines or external 'v' shapes, as well as built in items such as tanks and kill or cool boxes under the deck, the sides of these were often heavily glassed ply to form stiffeners within the hull. Other design features such as amount of deck as apposed to open boat would mean adding stringers across the hull to prevent the sides from flexing.
Older boats used timber as a former and glassed over them with the same resin and glass used to build the hull, often applied with a chopper gun, this device cuts a rope of fibreglass into short lengths that are sprayed onto the hull with a mixture of resin and catalyst that is fed from the same gun.
The problem with using timber is that standard poly resins do not stick to timber for more than a few years, and as poly resins are not that waterproof, water gets in, the timber rots and the glass alone is not strong enough, keep in mind that back then they only applied the glass to protect the timber and add a 'little' more strength.
On later hulls the timber was replaced with foam to form a shape for the glass to go over, but a lot more glass was added. This got rid of the problems with timber stringers and saved a little weight.
There is another problem you need to consider when repairing older fibreglass boats; Poly resin does not stick too well to old poly resin, it has to rely on the rough surface you leave to form a good key for a mechanical bond.
Epoxy resins will form a mechanical and chemical bond and can be up to 40% stronger and lighter.
Lighter because epoxy resin to stitched cloth ratio is close to one to one by weight.
Poly resin and chopped strand mat (CSM) needs a ratio of 3 resin to one mat by weight.
If you must add timber, be it ply, laminated or solid; give it at least two coats of epoxy after shaping, and another two coats after glassing, and remember Epoxy laminating resins are not UV stable, so you will have to protect them, paint or flow-coat is just fine.
I hope this helps.
Andavagoodweekend......
