Anodes sacrifice themselves to electrochemical corrosion instead of your engine and other metal parts - which is why it's worth checking their condition regularly.
Why anodes matter
When a boat's metal parts are in contact with water, galvanic corrosion occurs. An anode is deliberately made of a less noble metal that corrodes first, protecting the more expensive metals in the engine, drive unit and other parts.
Zinc, aluminium or magnesium?
Zinc anodes suit salt and brackish water, aluminium anodes work more broadly in both salt and fresh water, and magnesium anodes are typically used in pure fresh water. The wrong anode material offers poor protection or can even accelerate corrosion.
Anodes are always engine- and model-specific
Anodes are designed precisely for a specific engine model, so find the right anode by your engine brand: Mercury anodes, Mercruiser anodes, Yanmar anodes or Yamaha anodes.
When to replace an anode
As a rule of thumb, replace an anode once about 50% of it has corroded away. A fully corroded anode no longer protects other parts, and corrosion then moves straight to the engine's metal components. Check anode condition at least once a season, for example during spring maintenance.
Summary
· An anode corrodes on purpose to protect the engine's other metal parts.
· Choose the anode material based on water salinity: zinc, aluminium or magnesium.
· Replace an anode once about half of it has corroded away - don't wait until it's completely gone.
