The answer is different depending on where exactly the crack is. Firstly you must get it out of the water. Fibreglass will soak in water and cause osmosis later on.
If it is a crack then you need to figure out what caused it, there is no point filling it to have it crack again. If you scrope it along something that is simpler. You need to clean it out fully and dry it. This may neccessitate the use of a small grinder or something to get it cleaned back fully - if it is 1/8th" You get many differetn types of epoxy fillers make sure you get one that is suitable for underwater immersion. Plastic padding do one (try auto store or chandlery) as do International Paints. You mix the component parts of the filler together and sand it back. It should be good as new. It can be painted over as normal. If you want to reinforce it you can add glass fibre, although this makes finishing a lot more complicated.
Paul
August 2005
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