Epoxy-based barrier coats are generally one of the few recommended primers for aluminum when used below the waterline (such as on jon boats and pontoon boats). These primers have very good adhesion to properly prepared aluminum, and are designed to resist water penetration that could cause it to release from the metal.
Proper preparation usually involves abrading, sanding, or scuffing until the metal is bare and shiny, then applying an aluminum etch for the highest bond strength to the aluminum. To ensure the best results, always refer to the manufacturer's recommendations for the specific barrier coat.