above or below the waterline?....it makes a difference....you need to properly prep the metal with a sanding disk of sometype or have it blasted and get on it right away (within an hour)....wipe it down with prep solvent and then you need to etch it, prime with epoxy primer like Interprotect...then use Trilux type bottom paint ( made for aluminum/metal in salt water) below the waterline and a topside paint (I like a 2-part PU like Perfection) above the waterline...but thats your choice as to the manufacturer. Follow their directions carfully and you should be all set.
