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Your comment; With regel coating do I have to grind off existing gel coat or can I sand down exiting , repair damage areas, then gel coat over existing gel coat?

You can gel coat over existing gel coat after repairing damaged areas. Spray it with a cheap spray gun, such as the one sold by Harbor Freight for under $20. Its a siphon gun intended for spraying primers and has a 2.0 tip. You need a tip that large or larger to spray gel coat. There is alot of info on the web about spraying gelcoat, read everything you can before starting. I even practised on an old plastic garbage can first before tackling my boat.