I did a strip-to-the-hull stringer and deck replacement last year on an old fiberglass Glasscraft, and it turned into a major and pretty expensive chore, taking several unfun days.
The key to Part One, Demolition,was a grinder with a diamond blade,and a felt marker. We drew the line of the original deck on the hull before we cut it out, and also traced the position of the stringers as we removed the fiberglass structures that held them in place. Be sure you have an enclosed, well-heated garage, because you'll need at least a couple of days of drying out and warming up the hull after you remov the decay. Also be aware that you'll need intermediate support for the hull if you don't have long slats on your boat trailer, as the hull becomes very flexible without its stringers!
We replaced the old stringers with pressure-treated fir, and it took a fair amount of time to hand-plane and whittle them down to fit the hull. By all means remove the old stringers in as intact a state as possible to use for templates; opefully, they're less disintegrated than mine were.
My buddy is a professional fiberglasser, so that made it pretty quick to cut mat and cloth, mix resin and catalyst, and do the job, but it still took a long time to bond and glass the stringers into place. Before you do that, turn off the lights in the garage, and lie under the boat while someone shines a spotlight onto the hll. When you're looking through fiberglass-dust-coated goggles, it's easy to make a hard-to-detect slit through the hull with the grinder that will give your bilge pump an uncalled-for workout later on.
In the end, I wound up with a renewed hull at a lot less than a new replacement boat would have cost me, but if I had bought a used boat with a sound deck and hull, I'd have probably been ahead of the game. Above all, heed every word you see here about coveralls, goggles, and respirators. Fiberglass is no fun to inhale,get in your eyes, breathe, or wear to bed.
]
