The three main metal alloys used as galvanic anodes are Zinc, Aluminum, and Magnesium. 

Each alloy has advantages and disadvantages dependent on many variable situations, including water salinity, water temperature, water speed, current output, passivation, metals to be protected, and the anode’s designed life span. Care should be taken to determine that the best type of anode for given conditions is installed.

Zinc Anodes work well in salt and the upper saline levels of brackish waters. In lower levels of brackish and fresh waters, zinc doesn’t have the current output to fully protect. However, partial protection occurs.

Aluminum Anodes work well in salt and the upper saline levels of brackish waters. In lower levels of brackish and fresh waters, aluminum can film over by not sloughing its consumed metal which causes passivation and the possibility of a total loss of galvanic protection.

Magnesium Anodes work well in salt, brackish and fresh waters. Fresh water use is more prevalent due to the possible “over-protection” that may occur in the less resistant environments of salt and upper saline level of brackish waters.

For vessel protection, typical speed and how often the vessel is used can make a difference in choosing the proper protection. Changing habits in a vessel’s use can also change the type of anode required for protection. Since electrical currents change every time a vessel travels into different environments (waters), there is no absolute value to the corrosion rates of metals. Each vessel or structure must be looked at individually to ensure the proper protection.