Designed for saltwater.
Anodes are installed on boats for the purpose of sacrificial protection, also known as cathodic protection. Boats are made of various metals, such as steel, aluminum, and bronze, which can undergo galvanic corrosion when immersed in an electrolyte like seawater. Galvanic corrosion occurs when two dissimilar metals are in electrical contact in the presence of an electrolyte, causing one metal (the less noble or more reactive metal) to corrode rapidly while the other metal (the more noble or less reactive metal) remains protected. Anodes, typically made of metals like zinc or aluminum, are deliberately installed on the boat's hull and underwater fittings. So the anode "sacrifices" itself rather than let the sittings corrode.