How to Repair a Hole in a Boat
If you remember the first time you "wrinkled" the fender of a car, odds are that's the way you feel about the first hole in your boat, perhaps the result of an unfortunate encounter with a submerged log, or another boat. Fortunately, a boat's fiberglass hull is forgiving and the repair, "is less patch than graft--a new piece of skin indistinguishable from the old," according to Boat Owners' Association of the United States' boating expert Don Casey.
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Things You'll Need
- Scissors
- Knife
- Screwdriver
- Paste wax
- Acrylic film
- Duct tape
- Epoxy resin and hardener
- Denatured spirits
- Disk sander
- 36-grit sanding disk
- Putty knife
- Gel coat paste
- 1 1/2 oz. fiberglass mat
- 6 oz. fiberglass cloth
- 320-grit sandpaper
Instructions
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Cut the damage away with scissors, a knife or whatever it takes. Loose material will make the repairs more difficult. Casey advises tapping around the area with the plastic handle of a screwdriver to check for delaminated fiberglass, where damage is internal but not visible: "Solid laminate sounds sharp, delamination dull," according to Casey
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Wax the exterior surface of the hull around the hole. This keeps any material that comes through the hole from adhering to the outside of the hull.
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Cut a "backer" from thin acrylic film that's 2 inches larger than the hole and tape it over the hole, on the outside of the hull, with duct tape. Mix the epoxy resin according to the directions that come with the resin. If the directions tell you to mix 1 part resin with 100 parts epoxy, four drops of hardener per ounce is a good approximation.
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4
Step inside the boat and go to the location of the hole. Use denatured spirits to remove any wax on the surface of the hull around the hole. Use a disk sander with a 36-grit sanding disk to grind a bevel around the hole with a 1:12 slope. To find how far from the hole to start the slope of the bevel, multiply the hull thickness by 12: If the boat hull is 1/2 inch thick, multiply 0.5 by 12. The answer, 6 inches, is how far from the hole the bevel should extend, to form a long slope from the inside of the hull to the edge of the hole, giving the best gripping power for the repair.
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Use a putty knife to spread gel coat paste that matches your boat's color over the inside of the acrylic "backer." Apply a coat about 1/32 inch thick, about the thickness of a toothpick, to the inside surface of the acrylic film "backer."
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Lay the first layer of 1 1/2 oz. fiberglass mat over the hole. Cover the fiberglass with epoxy resin and work the resin into the fiberglass mat with the blade of a narrow-blade putty knife.
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While the resin is still wet, apply another layer of 1 1/2 oz. fiberglass mat and another layer of resin, working the resin into the mat. Follow this with a layer of 6 oz. fiberglass cloth, again working the resin into the cloth. Then a layer of mat and resin, then a layer of cloth and resin, alternating until the hole is filled. Finish with a square piece of mat and resin to cover the hole and the ground area.
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Remove the "backer" from the outside of the boat after 24 hours, to allow the gel coat time to cure. Sand the area on the outside of the hull with a disk sander and 320-grit sandpaper. Allow the resin to cure completely, both inside and out. Touch up the gel coat on the exterior of the repair with gel coat paste and re-sand, if necessary. Wax the exterior of the boat.
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