Applied according to instruction, it is very effective in controlling marine fouling. The leading cause of corrosion damage is galvanic corrosion, the electrochemical interaction between different metals. It is most hazardous where lower units, both outboard and stern drive, are immersed in salt water, brackish water, and many inland waters with high conductivity caused by pollution. The corrosion reaction occurs when electrons flow between dissimilar metals connected or grounded through water. In the process, one of the two metals is eaten away.
Sacrificial anodes are available in several forms.
MerCruiser stern drives and most Mercury, Mariner, and Force outboards utilize a trim tab on the antiventilation plate. Stern drives have additional anodes mounted at the outer transom plate. A transom-mounted anode kit is available to provide additional protection, if deemed necessary. The anodes' main purpose is for corrosion protection. By their very nature, they deteriorate rapidly and must, therefore, be constantly inspected and regularly replaced.