Anode protection

[Bavaria 390]

Good day!
The body of the seldrive is made of aluminium alloy.
The anodes are zinc anodes.
How can a zinc anode protect the case as it is on the right in the electrochemical series.

[Salty]

Probably for much the same reason that "IF" you coat your saildrive with copper based antifouling (Dont ever do that, not even by mistake !!), the aluminium would corrode very rapidly in favour of the copper in your antifouling paint. The only time you would need a different (non zinc) anode, would be if your boat was sailing in fresh water. Take care to get your anode from a responsible supplier, as there are some cheap knock offs on the market which might let you down, and that would be a very expensive situation to have to rectify.

[Yngmar]

Here's a galvanic series chart for saltwater:


https://cathwell.com/app/uploads/2019/09/galvanic_series_diagram_calomel.png

As you can see, zinc anodes are more anodic than the aluminium alloy range, therefore the zinc anode will erode and protect the saildrive (as long as it is present and in electrical contact with it).

The left/right axis is arbitrary and charts can be drawn in either direction.

[Bavaria 390]

Thank you friends!