There are epoxies developed for the offshore drilling rigs that are available to us. They were specifically designed to be applied underwater and achieve a molecular bond as well as mechanical bond. If you decide to repair in the water do a google search to locate this type of epoxy. If you haul, bevel the edges of the hole to allow for a few layers of glass on the outside. Fair, barrier coat, bottom paint.
Cal 9.2 #19 SilverSwan