Inspecting and replacing the sacrificial anodes on an outboard or sterndrive is an important maintenance task that is often overlooked by boat owners. Get in the habit of inspecting anodes several times during the season. The anodes are designed to protect the outboard or sterndrive from galvanic corrosion, which is most common in a saltwater environment but can also occur in freshwater. An anode corrodes, or “sacrifices” itself, and protects all the metals of the outboard or drive. Because many sacrificial anodes were once made of zinc, they are simply called “zincs” by many boaters. Today’s sacrificial anodes are made from a special aluminum alloy designed for this purpose. They function very well in both saltwater and freshwater applications.

An anode should be replaced when about half of the anode has been depleted to corrosion. On many outboards, one anode doubles as a small trim tab on the underside of the anti-ventilation plate, a good location because it’s near the propeller and is easy to see and inspect. When replacing this anode, it’s important to align the new anode at the same angle as the old anode. To work well, the anode also needs to have good contact with the metal it’s attached to. Make sure that the mounting surface where the mounting bolt attaches to the anode and the anode touches the aluminum drive housing is free of corrosion and other material build-up. It may be helpful to use a fine-grit sandpaper to clean the area before installing the new anode.

Replacing anodes is a relatively easy DIY task, and Quicksilver® replacement anode kits are available for many popular outboards and sterndrives, including popular models from Mercury®, MerCruiser®, Yamaha®, Suzuki®, Evinrude®, Honda® and Volvo Penta®. Quality Quicksilver replacement anodes meet OEM specifications and are manufactured from cadmium-free, environmentally safe aluminum. Your owner’s manual should help you locate the anodes for your engine model.

PRO TIP: To function, the anode needs to be in contact with the water. Never cover an anode with touch-up or anti-fouling paint. Keep anodes clear of barnacles and other marine growth. Anodes may develop a skin coat of corrosion, which can be cleaned off with fine-grit sandpaper.

What is galvanic corrosion?

Galvanic corrosion occurs when two dissimilar metals are immersed in an electrolyte, creating a low-voltage battery. On your boat, the dissimilar metals could be the aluminum gearcase and the stainless steel propeller or other stainless steel hardware, while saltwater acts as an excellent electrolyte. The aluminum component will have a negative charge in relation to the stainless steel and will be consumed in the process of generating an electric current through the electrolyte. This process can cause significant damage rather quickly, especially when the boat is moored in the water. To protect the aluminum parts of the outboard or sterndrive, a sacrificial anode made of a more active metal is placed on the gearcase or transom bracket. The anode sacrifices itself to protect other metals on the engine.

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