Things You'll Need
steel rod, 1/8 inch long and three times the length of the cracked area
Sand paper and disks, 60, 100, 200 and 400 grit wet-dry finishing paper
Fiberglass resin mix
Fiberglass gelcoat kit
Plastic fiberglass spreader tool
Nylon painter tape
Truck bedliner spray and sprayer
Fiberglass boat wax/sealer
A damaged fiberglass canoe keel should be repaired as soon as possible to prevent further damage to the structure of the boat. You'll want to clean up the damage, replace the damaged material and then restore the gelcoat that protects the finish. If you've got an older, heavily worn boat or your canoe spends a lot of time in rough water, taking hard strikes or misuse, you might want to add a second layer of protection while you are at it.
Repairing the Keel
Sand the area around the broken keel to remove the cracked fiberglass and gelcoat. Sand a deep "V" groove in the old damaged keel with the disk sander to make a bed for the repair. Extend the groove into the unbroken keel on either end of the broken area, the length of the damaged area in both directions from break. The metal rod should lay well inside the groove when complete.
Lay the metal rod in the "V"and cover with epoxy putty. Knead the putty thoroughly and press it into the groove. Shape the top of the putty to reproduce the shape of the original keel over the groove. Allow to cure for 24 hours, then sand smooth.
Mix fiberglass resin according to the manufacturer's instructions. Paint the resin over the area to be repaired, then press a layer of fiberglass cloth over the wet fiberglass. Paint the top of the cloth with more fiberglass resin and allow to harden and cure overnight.
Sand the cured fiberglass smooth. Mix fiberglass gelcoat according to manufacturer's instructions, add colorant to match the color of your boat as nearly as possible. Apply the gelcoat over the fiberglass repair and allow to cure overnight.
Sand the keel of the boat along it's entire length with very fine, wet/dry sandpaper.
Protect the Keel
Wipe down the keel and area on either side with acetone. Tape the hull along either side of the keel with a strong tape with nylon strings embedded in it. You'll want to mask the rest of the boat except for directly over the keel and an inch or two on either side.
Take the canoe down to a local garage that does spray-on pickup bedliners. Bedliner material is sprayed on with a gun that mixes a two-part chemical that dries in seconds. The bedliner tech may suggest spraying the whole bottom of the canoe and you can do that if you want, but be aware; spraying the whole hull can almost double the weight of the boat. Spraying only the keel protects the keel without adding more than a few pounds to the weight of the boat.
Pull up the tape as soon as the bedliner is sprayed on or you'll have to cut it away. If you quickly pull the tape before the bedliner material sets, you'll have a nice clean edge without having to use a sharp edge on your freshly repaired hull.
Bring the boat home and wax the entire hull with fiberglass boat wax. If you'll wax the boat at least once before the season, it will help protect the fiberglass from sun damage, especially if you use a wax/sealer that has a sun protectant in it.
Place the canoe out of the weather for a few days to let the repair set and fully cure before taking the boat out on the water.