Caring for anodes

Tips from the experts at boatcare for checking and replacing anodes

- Katy Stickland

When it comes to keeping your boat shipshape, an often-overlooked yet critical maintenance task is checking and replacing sacrificial anodes. These small and relatively inexpensive items act as a protective barrier against galvanic corrosion, saving your engine, propeller, and other underwater metallic parts from costly damage. We use the term 'relatively' because in some cases they're actually quite expensive, but not when compared with the kit they are protecting. Here we'll explain why anodes matter, how to check them, and the step-by-step process for replacing them.

What are anodes and why are they important?

Anodes are made from metals such as zinc, aluminium, or magnesium, and are designed to sacrificially corrode instead of your boat's more valuable metal components. This could include anything from bronze fittings such as propellers and stern gear, through-hull valves, rudders, and trim tabs -all of which are either high-value items or integral to the watertightness of your hull. The process by which these anodes work is called cathodic protection, and it works because when two dissimilar metals that are electrically bonded to each other are immersed in an electrolytic fluid, such as seawater, the more reactive of these metals will corrode first.

This is especially important when you consider an item such as a saildrive, which could be made of an aluminium casing, steel shafts, bearings, and gear sets, all of which are made from different grades of different metals.

A new saildrive is certainly not a cheap bit of kit, so it's definitely a good idea to keep it well protected!

Different anode types and materials