Not much to say about the issues until we hear both sides of the story.
Although there is a composite structure where there is tensile strength of the fibers there is not enough resin to provide compression strength. It really depends upon the gel coat for compression strength which is okay but it's on the wrong side of the laminate, it's strong against a push from the inside of the hull but not a push from the outside. It wasn't until the next morning I asked myself, "but where are the yellow stringy fibers that they talk about when sanding Kevlar, why was I sanding into the laminate when kevlar can't be sanded and faired out?" Simple, it's not kevlar. It's fiberglass.
Resin or gelcoat dont add much compression strengt. It's always the fibers that add strength, both in compression and tension.
If the outer laminate is kevlar, you should see "the yellow stuff" after sanding away the gelcoat. There might be a glass cover outside the kevlar depending on how they build their hulls, but I would think you would be able to see the kevlar. You
dont want to sand into the kevlar, ever!
Cracks in gelcoat and laminate
I dont know how much you know about sandwich construction, but one question: Have you ever hit anything with the boat? Rocks, concrete etc? Cracks in the laminate is bad news and not something I would expect in a production boat. If you e.g. dont use beachwheels but drag the boat over rocks or concrete you will ruin a sandwich hull in no time. Same for hitting submerged rocks or other solid stuff. There is no warranty covering such things. It would be good to see pictures of the damages and the hull you sanded with exposed laminate.
