Shop sacrificial anodes at West Marine.

Sacrificial anodes are pieces of relatively pure zinc, aluminum or magnesium that are fastened to underwater boat surfaces. They are designed to wear away and protect other metal parts against damage caused by galvanic corrosion.

What is galvanic corrosion?

When dissimilar, electrically connected metals are immersed in an electrolyte (usually saltwater) an electro-chemical reaction occurs which begins to corrode or “eat away” one of the two metals. The end result of this process is referred to as galvanic corrosion. Many people wrongly refer to this process as “electrolysis”.

Because boats tend to have many underwater metal surfaces (outdrives, thru-hull fittings, propellers, etc.) and because many are “wet stored” in the water, galvanic corrosion ends up being a costly problem if it is not controlled.

How do sacrificial anodes work?

In a galvanic or electro-chemical reaction, how fast a metal corrodes in relation to another depends on where the metals are located on the nobility scale. The nobility scale ranks the relative ease that materials are corroded when in a salt bath. Active metals, like zinc are at one end of the scale and “noble” or inactive metals like gold, silver and platinum are at the other, the passive end. Shifting this discussion to boats, a bronze propeller on a stainless steel shaft is more active in relation to the shaft. Because of this, if left unprotected, the propeller will suffer damage from galvanic corrosion. This is where sacrificial anodes come in. In simple terms, installing a zinc anode on the shaft will protect the propeller from damage by sacrificing itself in place of the propeller.

Anodes come in many shapes and sizes.

West Marine offers anodes in many shapes and sizes, since the places on a boat or engine that need protection are highly varied. Types of anodes include shaft anodes, rudder button anodes, hull anodes, prop nut anodes, engine anodes and anodes that are specifically designed for installation on outdrives.

Outdrive Anode Kits

Outdrive anodes are offered in kits which eliminates the need to purchase outdrive anodes individually. West Marine offers outdrive anode kits for all the major brands, including MerCruiser, Volvo-Penta, OMC and others. Outdrive anode kits are offered in zinc, aluminum and magnesium.

Aluminum, Zinc and Magnesium Anodes

Many boaters still refer to sacrificial anodes as “zincs”. This is understandable since until recently, anodes were nearly all made of zinc. However, in addition to zinc, anodes are now also offered in aluminum and magnesium. Traditional zinc anodes work well in saltwater. Aluminum anodes are recommended for salt- or brackish water and magnesium anodes are recommended for freshwater. Almost all the anodes that West Marine offers are manufactured by CMP Global and sold under their Martyr brand.