Aluminium anodes

[Odysseus]

I as I posted last year when I fitted an aluminimum anode to my 120 sail drive, well its been on one year now and worked very well.
I have posted photos for you to see, remember I go in and out of brackish,  fresh,  and salt water.

No calcification, still working well. If you get calcification,  well its a good fix for the problem.

Odysseus
Bav 38

[Yngmar]

How does an aluminium anode protect a saildrive made of aluminium? Shouldn't the anode be lower on the galvanic scale than what it protects? Or is it because the saildrive is really some aluminium alloy, putting it higher than the pure aluminium anode.

I always thought the choice for brackish/freshwater was Magnesium (and Zinc for seawater).

And what was your propeller anode made of, which seems to have worked much harder?

[BillGiles]

There is little difference between the electric potential of most aluminium alloys and pure aluminium. However, certain Al alloys have magnesium in them and make them very susceptible to corrosion.

[Odysseus]

I should have said alloy not aluminium,  as it is a mixture of metals,  however, if you look at new outboard motors they tend to have alloy anodes.
My problem was each year at lift out my zinc anode was completely calcified so I spoke to a freind in the marine industry (a metallurgist  ) and he suggested the change. Not only  does if appear to work better it's half the price of Zinc.
As you point out magnesium is the freashwater choice,  but if you are going in a mixture of waters multiple fixed anodes of differing metals are not practical.

Point 2, you noticed the prop anode had worn away, yes but for a Volvo folding prop, 3 years life is very acceptable, ask around!! Is it all down to the alloy anode, or the painting around the fixing holes on the prop anodes to stop them flying off, probably some of each. Do I see any sign of corrosion to prop, or leg, none I can detect after a very intensive inspection.

What I am offering the forum is my fix, sailing in salt, brackish, and freash waters, how many of you keep your boat in an estuary,  brackish water?
New prop anodes painted and ready to go on


Hope this helps.

Odysseus bav 38

[Yngmar]

Thanks for clarifying, now it makes a lot more sense to me. Do you happen to know what mixture these alloy anodes are made of?

[Odysseus]

Sorry no, but you can get them from Solent Anodes,  Southampton.

Google them

Odysseus
Bav 38

[Odysseus]

This is the spec on their site.
Odysseus
Bav 38