How do you paint an aluminum boat?

If boat has paint that is in good shape and you just want to change color, sand area with 400 to 600 grit then wipe clean with acetone,lacquer thinner or similar solvent then paint. If Paint is in bad shape strip chemically or sand to remove paint. Sand to 400 grit then you must use a etching primer then paint. It is not recommended that you paint below waterline.