As long as there is no structural damage, and if the gap is small enough, people tend to leave holes in their boats. However, the gaps can enlarge and lead to more serious problems. You don't need many tools of your own to do the repair job, just an electrical sander, or an electric drill with a sander attachment. You will need to purchase the actual repair kit itself. The kit should be a polyester resin fiberglass repair kit or a polyester resin with hardener.
Prepare The Area
Sand the edges of the hole until they're smooth. You should slightly increase the size of the hole and taper it; have the outside edge hole a couple of inches wider than it is on the inside of the boat. This gives good bonding room for the patching material. Clean the area (preferably with acetone, remembering that it is highly flammable) until spotless.
Address The Hole
Contouring the patch to the same shape as the hull is easier if you use a cardboard backing. Cut the cardboard around two inches bigger than the gap all around and cover in a plastic wrap, smoothing it out; this prevents the patch from sticking to it. Place the backing into the hole and bend to fit the contour of the hull. Fix it in place with tape. Get the roving (small bundles of fiberglass material) and fill the hole, cutting progressively larger pieces. Start with a small piece that covers just the hole, and build up the layers until the hole is filled.
Fill The Hole
Next, use clean pieces of regular card (found in stationary shops) or cut the flat side out of an old cardboard box, clean, and lay on the ground next to the boat. Take the patches out of the hole and individually lay them onto the card so they are separate. Mix the resin remembering to only prepare the amount of patches you can apply in thirty minutes, the time taken for most resins to harden. Working quickly, apply the resin to the smallest patch with a clean paintbrush; the aim is to have the patch soaked, not dripping. Fill up the hole with the wet patching material.
Cover the area with finishing fiberglass cloth, which you will need to cut to size. Place the cloth over the area without soaking it first. Paint the resin onto the cloth, until it is dark and wet everywhere. Allow the resin to dry; this usually takes around eight hours but refer to the instructions on the repair kit. You can then remove the cardboard backing, and carefully sand the area to a finish.
You can use a gel coat made by the manufacturer to match the hull, or buy a fiberglass rubbing compound to protect the repaired area. If you have further questions or need more help, contact companies like Chuck's Marine to ensure smooth sailing.