Aluminum is an ideal materiel for vessel hull and deck construction, most smaller fiberglass pleasure craft are fitted with Aluminum fuel tanks. While there are numerous advantages to aluminum, there are a few concerns that are mostly related to corrosion issues. Fortunately the majority of these issues are preventable or correctable if managed early on. All Aluminum forms a protective coating or oxidation when exposed to air and is self healing when scratched, this oxidation performs well even in damp environments, but when Chlorides are present, the attack begins almost immediately. Aluminum forms a very strong bond with oxygen and desires to return to its natural state. The melting point of aluminum is 1,221° F but the melting point of the very thin oxidation coating is actually considerably higher at 3,762°F! The ideal protection for aluminum is the natural oxide coating. In order to paint aluminum you need to remove the coating that protects it. In addition, the coating reforms almost immediately after removal making it difficult to successfully apply coatings.
Marine fuel tanks;
With few exceptions, all small pleasure craft Aluminum fuel tanks are constructed of 5052H32 alloy. While not a true marine alloy, 5052 has good corrosion resistance, excellent weldability and is the only Aluminum plate that can be bent easily with minimal radius. Most of these fuel tanks are located aft on centerline below deck and many tank compartments are poorly ventilated. Fuel tanks that are secured with foam or put in a constant damp environment have a much higher failure rate that tanks that have excellent air circulation and drainage. Coating tanks can be helpful (Required for new gasoline powered vessel construction after August 2013) but prepping for surface coating requires etching of metal surface, in other words removing the oxide that defends the metal surface in the first place. The plastic inspection ports (Usually) found above the tanks in the vicinity of fuel fills, lines and vents and senders have O-rings that are never properly serviced allowing water and contaminants to land directly on tank. If the vessel owner can establish a way to periodically wash and dry the compartment or bilge and maintain inspection ports, this will significantly extend the life of the tank. Opening of deck hatches and inspection ports on dry sunny days as long as it is safe to do so or they are re-secured when task is completed. If significant fuel odor and excessive pitting is observed, the only sure fix is to replace tank and or hoses. There is no crystal ball to predict the lifespan of a particular tank and complete removal for inspection is the only sure and safe way to determine condition of tank. There is no way to repair aluminum pits in most recreational aluminum fuel tanks, short of temporary stop gap measures. Fuel tank inspection and service is one of the most critical areas on board your vessel, particularly gasoline fuel systems!!