Anodes
Sacraficial anodes offer protection against corrosion caused by electrolysis to engine cooling systems & underwater metals, sterndrives, propellers & outboards for example. This is especially inportant for boats stored in marinas due to stray currents from shore power instalations. These should be replaced regulary to ensure your investment is protected.
Anodes are produced in three metals, magnesuim for fresh water, zinc was traditionally for sea water, but aluminium is fast replaing zinc for both sea and estuary.