smallboat

You have a blistering problem. This occurs when a boat is kept in the water as opposed to on a trailer and the fiberglass lamination becomes wet and separates from the gel coat. I suspect the previous owner kept the boat in a slip. Yes, fiberglass hulls made using polyester resins can and will absorb moisture. To repair, grind off the gel coat surrounding all of the blisters. Allow the hull to dry out - use a moisture meter to verify. Fill the blisters and areas you have sanded with a filled epoxy mix. Since this appears to be a cosmetic repair, use glass beads or micro balloons as the filler. After curing and sanding, paint the entire bottom with a barrier coat paint - Interlux and others make them. This is an important step. Follow with a good topcoat paint. You don't need a bottom paint unless you plan on keeping the boat in the water. The new two part linear urethanes are extremely tough and will work very well. Blisters are mostly a cosmetic defect but can lead to greater problems if the hull lamination becomes saturated. Not typically a problem with trailered boats but fix the problem now. Water absorbed into the hull lamination will not effect your stringers and foam unless you have a hole in the boat.