Zinc Alloy Weld-On/Bolt-On Hull Anodes (Z-Guard®): Corrosion may be defined as the deterioration of a metal due to a reaction with its environment. For corrosion to occur areas with different electrical potentials must exist on the metal surface. An electrical current will flow between water and fittings made of different metals, causing some of them to corrode away. On Wooden and GRP boats the propeller, shaft, p-bracket and skin fitting are at risk, while on a steel hulled vessel the whole underwater area is vulnerable to costly and potentially dangerous damage. Hull Anodes are used and designed to prevent corrosion of the entire immersed steel hull area including exposed shafts, brackets, rudders and propellers.