Which anode material is used for what application?
Sacrificial Anodes are placed on hulls, propeller shafts, rudders, trim tabs, outboard engines, stern drives, and in the cooling system of most inboard engines to protect metal parts from galvanic corrosion.
Galvanic corrosion occurs when dissimilar metals, such as an aluminum stern drive and a bronze through-hull, are placed in an electrolyte solution such as seawater. Dissimilar metals are those metals which have different corrosion potential (measured in volts) as determined by the Galvanic Series, and the most common scenario in boating is current passing from the more noble bronze to the less noble aluminum. This transfer of current results in deterioration of the less noble metal. The addition of a zinc actually increases current activity between the metals, but because zinc is the least noble of the three metals in this example, corrosion damage is primarily confined to the zinc itself when properly installed.
Marine anodes are available in zinc, aluminum and magnesium metals to protect different hardware items and other metal boat components. Plate, tear drop, rudder, shaft, tapered, mercury outdrive (specifically designed for use with Mercury engines), zinc pencils, donut collar, Johnson-Evinrude (for use with Johnson-Evinrude engines), weld-on, and other shapes and styles. The corrosion resistance results provided by proper application of boat zinc is incredible and will save time and money in the long run.