Hull and Transom Anodes

Sacrificial anodes such as the hull and transom anodes you see on this page are pieces of relatively pure zinc, aluminum or magnesium that are fastened to the hull or transom of boats. They are designed to wear away and protect other metal parts against damage caused by galvanic corrosion.

What is galvanic corrosion?

When different metals that are electrically connected are submerged in an electrolyte such as saltwater, an electrochemical reaction can occur. This reaction often results in the corrosion and gradual deterioration of one of the metals. The process is referred to as galvanic corrosion. It's a common misconception for individuals to label this phenomenon as "electrolysis." Given that boats that are stored in the water often have numerous submerged metal components, such as outdrives, thru-hull fittings, and propellers, sacrificial anodes are installed to protect against the expensive damage that galvanic corrosion can cause.

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.

Types of Sacrificial Anodes

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, transom anodes, prop nut anodes, engine anodes and anodes that are specifically designed for installation on outdrives.

Types of Hull and Transom Anodes

Hull anodes vary greatly in terms of their shape, size, material and attachment method. Examples of hull anodes include rectangular "plate" anodes, "teardrop"-shaped anodes and a variety of other anodes whose shape defies description.

Attachment Methods

While most hull and transom anodes are designed for bolt-on installation, some are designed to be welded on. Examples of bolt-on anodes include Martyr's "Diver's Dream" plate anodes which feature slotted bolt holes which enables the anode to easily install on to the existing bolt studs (whose spacing varies) on the transom of boats.

Weld-on anodes are cast around a steel or aluminum strap which is left exposed at either end of the anode. The exposed part of the strap is what gets welded to the hull or transom of a steel or aluminum boat.

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.