Shop shaft anodes at West Marine.
Galvanic corrosion is a type of corrosion that occurs when two different metals are in contact with each other in an electrolyte, such as seawater. The difference in the electrochemical properties of the two metals creates a galvanic cell, which causes the more active metal (the anode) to corrode at a faster rate than the less active metal (the cathode).
Types of Collar Anodes
West Marine offers a variety of anodes to protect boats from galvanic corrosion. Choices include streamlined collar and low-clearance shaft anodes. These anodes are typically fitted around the propeller shaft to protect the shaft, the shaft log and the propeller from corrosion. Where adequate clearance exists (such as with boats that have their shafts suspended from a strut) one or two streamlined collar anodes are typically bolted to the shaft. For limited clearance situations (boats with only a small amount of shaft exposed) low-clearance collar anodes are installed just forward of the propeller.
Zinc, Magnesium and Aluminum Anodes
Sacrificial anodes are made of a more active metal alloy (such as zinc, aluminum or magnesium) that corrodes preferentially to the less active metal (such as stainless steel, bronze and other alloys) used in boats. As the anode corrodes, it releases electrons that neutralize the corrosion-causing ions in the electrolyte, thus protecting the less active metal parts of the boat.
Select the correct anode alloy for the type of water where you use your boat.
For optimum protection, it is important to select the correct anode alloy for the type of water where you use your boat: zinc for saltwater, aluminum for salt or brackish water and magnesium for freshwater.
Anodes should be checked regularly.
It's important to note that anodes will wear out over time, so it's important to check them regularly and replace them as needed. As an anode wears down, it's effectiveness as an anode will also be reduced, and the protected metal parts will be at risk of corrosion.
Conclusion
In summary, collar and shaft anodes are used to protect boats from galvanic corrosion by corroding preferentially to the metal parts they are protecting. They should be regularly checked and replaced as needed to ensure proper protection.