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What purpose do anodes play in yacht propeller design?

Westerly Fulmar yacht with 16” 3Blade FeatherStream

Anodes play a crucial role in yacht propeller design as they protect the propeller and other metal components that sit below the waterline. They are a relatively cheap way of protecting the key parts of your yacht from corrosion, caused by salt water and electric currents.

The anodes on a yacht are often known as “sacrificial anodes” because they degrade during sailing rather than other metal parts of your yacht. In fact, seeing an anode gradually being eaten away during the season should be viewed as a good thing, as it shows the anode is doing its job properly.

Galvanic Corrosion

Galvanic series noble metals - Wikipedia

When parts made from different metals are joined, or connected to each other while in water, then something called galvanic corrosion can occur. As the two different metals come into contact with the seawater (acting as an electrolyte) an electrochemical reaction takes place. A voltage is produced, effectively creating a battery between the two metals, which causes one of the metals to corrode.

The metal part that corrodes will depend on their relative position in the galvanic series. So, of the two parts; the one that is lower down in the galvanic series will become the cathode, and the higher one up in the series will be the anode. The anode in the part that will corrode.

In the real-life example where a brass propeller is connected to a stainless-steel prop-shaft, the brass propeller is the anode, and the prop-shaft is the cathode. This means the brass propeller would be the component to suffer corrosion.

Why anodes are important?

An anode is used as a target for the corrosion instead of the yacht propeller. When an anode is installed correctly, it creates an electrical current with the propeller and other metal parts. The circuit that is created redirects the electrical current, ensuring that the anode corrodes sacrificially instead of your prized prop.

Anodes are typically made from zinc, aluminium or magnesium alloys – i.e. made from a metal that is more electrically active than the other metal components they are protecting. Because these types of metal have a higher tendency to corrode, the propeller and other valuable components are protected. The anode gradually dissolves or erodes over time as it protects the propeller, shaft, and other submerged metals.

Inspecting & Replacing your Anodes

As well as checking your propeller it is important to regularly inspect your anode to ensure they are functioning effectively. Anodes can wear down at different rates depending on the condition and the usage of your yacht.

How often should I replace an anode

Check on the condition of your anodes and if they are significantly eroded, then they should be replaced. Make sure you inspect them at least once a season, and in our experience, err on the side of caution and replace them if they are 50% of their original size.

Read our blog on servicing a Darglow Feathering propeller that includes a section on replacing an anode.

Contessa 32 FeatherStream Propeller Service

Protecting your prop with an anode

Sacrificial anodes are a key element of yacht propeller design as they can help prevent or minimise galvanic corrosion – the bane of many yacht owners which can cause costly damage and affect performance.

By installing and maintaining your anode correctly you can ensure their effectiveness in protecting the propeller and other underwater metal components.

Buy Yacht Anode online

Our propeller anodes are manufactured with military grade Zinc 18001k, to provide the best corrosion protection. Most prop anodes and accessories are in stock and ready to ship same day.

Visit our shop to purchase a new anode for your FeatherStream propeller.

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