Despite their relatively simple appearance, boats are tricky machines—especially their engines. The entire concept of a boat engine seems counterintuitive, given that it spends most of its life underwater and water has a tendency to corrode and rust almost everything. The breakdown happens when two metals are in contact with an electric current running between them. The current is carried by metal ions that “sacrifice” themselves and then leech into the water. This process is called galvanic corrosion, and it’s especially common on an aluminum propeller attached to a stainless steel shaft. Boat engine anodes, however, prevent this. Due to a chemical process that introduces a third metal, these sacrificial anodes for boats corrode instead of the other metal boat engine parts they’re attached to. Each type of water requires an anode made of a different metal. Zinc anodes are ideal for saltwater. Aluminum anodes work best in brackish water, which is a mix of fresh and saltwater. Then in freshwater, use magnesium anodes to prevent corrosion. Because every boat engine is different, boat engine anodes tend to be design-specific. They’ll work for certain makes and models, but not others, making it important to find an anode that matches your specific engine. Anode installation and replacement is usually pretty simple, though professional installation is recommended if you don’t feel comfortable tackling it yourself. Use our Marine Engine Parts Selector Tool to find the right engine parts for your boat.