TOPIC: Stringers enhanced strength

Received advise from ( Bill.Cars) the stringers on 1958 bee sapphire consists of 1\2 cut cardboard tubes 2" high. He said to build up Laun ply wood between stringers and heavy fiberglass over . Has any one done this? What does heavy fiberglass mean ? Between each layer (1\8" ) plywood? I'm fiberglass dummy?

Bill and many others are the experts, so hopefully a few will chime in. I can tell you that my 1958 and 1965 fiberglass hulls ( that don’t use false floors or stringers because one is a tri-cat and the other is a fairly flat bottom with rounded side like a typical 14’ aluminum fishing boat style, but uses a wooden external keel with the laminated fiberglass hull over it and also uses 2 full cross bench glassed seats to stabilize hull from flex) ... but what I am getting at is both of these hulls embedded plywood flat on the inside bottoms of each hull that were bedded in with what appears to be several lay-ups of glass and polyester resin to stiffen the bottoms from flex puckering when you cross waves of rough water to a point. I cut the one floor section where it butted into the transom and the little 13 foot boat appeared to use 3/8 inch thick plywood. Though the transom was rotten from holes below the waterline, that floor was fully encapsulated and after 50 years, there was NO rot or water stain... pretty good considering this boat was registered up to 2010. I am sure it had its fair share of water just sitting in that hull over it life... my take on this is if you don’t have screw holes penetrate the glass encapsulation of this floor wood and you do a good job, rot is not really a concern . When I bought the one boat, the transom had about 22 screws or bolts in it and the heavy motor tore the transom about 5” down. Ask Bill or others about how many layers of glass and resin and what kind of glass they recommend. They typically use polyester resin for glassing old boats because that is what was used in the early days. My understanding is that you can use epoxy resin with old polyester resin boats and it will hold... but I think stiffer... you just can’t go back with polyester resin over epoxy from what I have read. Others please jump in... my plywood floors in both boats that are laminated in glass still hold up well. Good luck.

I've seen that cardboard system used before and the tubes just disintegrate from standing water and that plugs up the drain holes...can become a nightmare.
Luan is just a very thin plywood mostly used as home floor underlayment before laying down tiles or laminate flooring. pretty cheap stuff at Home Depot etc. That being said I think what Bill is getting at is to stiffen the floor, cut some luan to fit between your stringers, doesn't have to be a tight fit, lay down a layer of glass mat on the bottom and then place the luan on top of the wet glass, repeat about 3 or 4 times and then put down a final heavy layer of fiberglass mat over the top of that and you'll have a beefed up hull strong enough to hold a heavy cooler filled with ice and beer.
When you go to a lumber dealer just ask for luan, they'll know what you want.
www.homedepot.com/p/1-4-in-x-8-ft-x-4-ft-Lauan-Plywood-466811/206639114