Aluminum anodes

When to use aluminum, when to use zinc?

Aluminum anodes are designed for salt and brackish water and are more efficient than traditional zinc anodes: they have a higher electrochemical capacity and lower weight. In freshwater, however, aluminum anodes often become passive – in this case, it's better to use magnesium. If you change cruising areas, it's worth changing the anodes accordingly.

Shape and dimensions: No room for compromise

Shaft anodes, rudder anodes, keel anodes, or hull plates – each installation position has its own geometry. External dimensions, hole spacing, and bore diameter are crucial. An anode that is too small will corrode too quickly, and one that doesn't fit properly will have poor electrical contact and provide little protection. If in doubt, remove the old anode and measure it directly – or note down the manufacturer's specifications for your engine or stern tube.

Installation and electrical contact

The anode must sit metal-to-metal: no paint or antifouling between the anode and the substrate, otherwise you will interrupt the circuit. Tighten screws firmly, clean the contact surface on the hull or drive of paint residues – that's half the battle. Anode paste or conductive greases are generally not necessary and can even be counterproductive.

When is the anode due for replacement?

As a rule of thumb: if the anode has corroded to about half its original volume, it's time for a replacement – check it at least once per season when lifting the boat. An anode that has hardly corroded can indicate poor contact or an incorrect alloy and should still be replaced.