Fighting Corrosion in Boating

Corrosion is a process that is greatly affected by the water that boats reside in. Over time, the metals that make up a boat's hull will develop galvanic corrosion due to constant contact with the water. That is why boat manufacturers will use materials other than fiberglass or wood to create the boats. Aluminum is also used, but not without proper measures to slow the corrosion process. Although the slow decline of an aluminum-hulled vessel seems inevitable, magnesium alloys can be used to prolong the process, thereby extending the life of the boat.

Hull Material
Aluminum magnesium alloys are being used in freshwater boat hulls, but the majority of hull material is made up of wood or aluminum. The reason is the vulnerability of magnesium outside of freshwater. Magnesium is known for its protective ability. It creates a protective film around itself that serves to hinder the corrosion process. In freshwater, this is what occurs. The magnesium mixed inside the aluminum creates a protective shield around the boat. In salt water, however, the magnesium reacts unstably with accelerations in the corrosion's instead of the protection found in fresh water. The reason is the metal's interaction with the salt in the water.

Researchers are working with magnesium alloy combinations in order to come up with a combination that would counteract the saltwater to allow the magnesium to build its protective shielding. So far, it is known that iron, nickel, copper, and cobalt kick-start the corrosion process more than any other elements.

Magnesium Anodes
To deflect some of the corrosive energy on the hull, boat builders will place an anode on the hull made of a metal that is more corrosive than the material that the hull is made of. This is where magnesium is commonly found on boats. Called a sacrificial anode, the anode is placed on the hull as an ideal place for the electric current that causes the galvanic corrosion to flow through. The corrosion is an electrochemical reaction that is attracted to the anode. By placing a sacrificial anode on the hull, the boater creates a protective zone on the rest of the boat in the form of a cathode or area of reduced current flow. Aside from the anode, there is very little metal found on the hull of a boat.

In boating, magnesium's protective and corrosive properties are beneficial depending on the type of water that the boater is traveling in. The metal forms a protective force field in freshwater to deflect the corrosive energy, but in saltwater it is a like a magnet for the current. It would be amazing if researchers found a way to harness these opposing powers to create a corrosion-proof hull.