My kayak spends over 25 days on Georgian Bay every summer and as a result suffers many scrapes. To patch the keel has therefore become the end of summer routine for me. I am not talking a cosmetic fix of scratches to the gelcoat, what I mean is damage to the keel that exposes fiberglass. Over the years I tried many different products as the patchwork on my kayak can testify. None has been satisfactory mainly because all of them were rather runny and therefore could not create a protective (and sacrificial) layer thick enough.
Three years ago I came across a wonderful product and never looked back. It is the Six10Tm Epoxy Adhesive from West System. Here is a description from the West System flyer: A two-part thickened epoxy adhesive in a convenient, self-metering cartridge. For permanent, waterproof, structural gap-filling and gluing. Bonds to wood, fiberglass, metals and masonry. With the included 600 Static Mixer attached you can dispense fully mixed adhesive right where you need it using a standard caulking gun. Working time is 42 minutes at 72oF (22 °C), cures to solid in 5-6 hours and takes high loads in 24 hours. Contains 190 ml of resin and hardener. Extra 600 Static Mixers available.
It is very easy, with no mess, no need for mixing, containers etc. I clean the areas I want to repair with soapy water, let dry, then tape around with masking tape. Then dispense the epoxy (it has a consistency of a tooth paste) on the area, smooth with a putty knife and let polymerize for 24 hours. Next day I sand it with sandpaper of decreasing grit size and polish with wax polish. There is a stopper included that allows you to close the cartridge (and separate the two components). To my surprise, I was able to use it again the next year! I just had to buy a new mixing spout (the 600 Static Mixer).
Now my kayak is ready for next summer!