A 3M marine epoxy with a filler, they have different fillers for different jobs. West Marine has knowledgeable associates if you have a store nearby. I have used it to repair damaged hulls on small sailboats. Stronger and waterproof which fiberglass is not. Gel coat after the epoxy. Any cracks that extend out from your repair need to sawed out and end drilled. This advice is only pertinent if don't consult a professional, the damage looks extensive.