With the recent purchase of a jet ski, I had a couple of stone type 10 cent size dings and Septone makes a Gelcoat DYI for 21 dollars at BCF (white) and its a two part mix with hardener at 1:50 parts. If you only have small areas that expose the fibreglass then this will assist. Just mix up a small batch in a milk container lid and it mixes well then around the 3-4 min goes off in a few seconds. My first batch I missed getting to the boat!!! Anyway the preparation is about cleaning the affected area and I am told rubbing finally with styrene will assist to get a complete bond. I've finished the job today with a finishing sander point and now for the polishing part, just a bit of effort and anyone can preserve the bottom. Hope this assists, Geoff