You need wax & grease remover for autos, sometimes the old timers called it prep-sole.You can get this stuff at you local auto paint store or nappa stores.Get cross fire #15250 and then use a red scotch brite pad to scuff it with or wet sand it with 600 grit. Wash your boat first with the wax & grease remover before sanding.Then after sanding it,then rewash it again before paint.