Aluminium anode on galvanized anchor/chain?

[flightlead404]

I don't see too many folks with anodes on their galvanized anchors and chains, I do see lots of people complaining about the galvanizing not lasting.

Galvanizing is essentially zinc plating, right? The same stuff, more or less, that many sacrificial anodes are made from.

Aluminium is ness noble than zinc, would an aluminium anode on galvanized anchor and chain help preserve the galvanizing?

[grantmc]

Originally Posted by flightlead404

...
Aluminium is less noble than zinc, would an aluminium anode on galvanized anchor and chain help preserve the galvanizing?

Yes of course. Aluminium anodes (usually welded) are very common on things like lobster pots, why not anchors and chain too.

Aluminium or zinc? Most people have a preference, but for many that preference is based on the myth that because zinc anodes feel a lot heavier, they are therefore more effective. Not necessarily true - aluminium anodes are lighter, but that is actually one of several advantages they have over zinc. Obviously lighter anodes are easier to transport and handle, but – and here’s where it gets technical – the electro chemical capacity of aluminium is around three times higher than of the same mass of zinc, which means you get longer protection for less bulk. Aluminium anodes also have a relatively high driving voltage, so it has better distribution of the electrical current, compared to zinc. Another advantage of aluminium is that it doesn’t contain cadmium (zinc has a small amount) which is harmful to marine environments. Also, aluminium anodes are significantly cheaper than zinc for the same electro chemical capacity.

[Benz]

Originally Posted by grantmc

Yes of course. Aluminium anodes (usually welded) are very common on things like lobster pots, why not anchors and chain too.

Aluminium or zinc? Most people have a preference, but for many that preference is based on the myth that because zinc anodes feel a lot heavier, they are therefore more effective. Not necessarily true - aluminium anodes are lighter, but that is actually one of several advantages they have over zinc. Obviously lighter anodes are easier to transport and handle, but – and here’s where it gets technical – the electro chemical capacity of aluminium is around three times higher than of the same mass of zinc, which means you get longer protection for less bulk. Aluminium anodes also have a relatively high driving voltage, so it has better distribution of the electrical current, compared to zinc. Another advantage of aluminium is that it doesn’t contain cadmium (zinc has a small amount) which is harmful to marine environments. Also, aluminium anodes are significantly cheaper than zinc for the same electro chemical capacity.

Grant, this is interesting. Does the alloy matter, or could I wrap the bail of my anchor tightly with aluminum MIG wire and have it act as an anode? I have a lifetime supply of MIG wire I could just replace every few weeks.

[rslifkin]

Originally Posted by Benz

Grant, this is interesting. Does the alloy matter, or could I wrap the bail of my anchor tightly with aluminum MIG wire and have it act as an anode? I have a lifetime supply of MIG wire I could just replace every few weeks.

I'm not sure if that would be the most effective alloy. "Aluminum" anodes are typically made of Navalloy, which is a blend of Aluminum, a little bit of zinc and a tiny bit of Indium.

[HeywoodJ]

Aluminum alloys have a pretty wide voltage range. Your zinc anode material (an alloy itself) has a voltage of ~1.05V compared to a silver reference electrode in seawater. An aluminum/gallium (Navalloy) anode has a voltage of ~1.1V.

OTOH, the alloy used in outboards and sterndrives has a voltage of ~0.75V. This is why you would see a zinc anode on aluminum outboards and stern drives, with the higher voltage potential the zinc can protect the aluminum, whereas with Navalloy the aluminum can protect the zinc (in theory - the voltages are so close that in real life it is probably a wash).

[captstu]

Galvanic protection depends on good electrical conductivity. Welding or attaching an anode to an anchor might help significantly, but chain - I doubt it. After a few hours in the water, I suspect the electrical connections within links are poor as coorision develops.

Save your money, regalvanize the chain from time to time.

[jhulmer]

Very interesting using aluminum. May warrant testing. Peeked my curiosity.


Zinc Anodes are heavier but we are talking about an anchor here. It's kinda how they roll, don't you think?
However, it begs the question: How much more protection would the addition of an anode add? I would think the anode and the zinc coating would be at the same potential and thus corrode at the same rate. If true, the then the zinc would still expose raw metal at the same rate as without the anode. After which the anode would protect the exposed metal. Yes/No?
Jim

[svchances]

Zinc is for salt or brackish water. Aluminium is for fresh water. Look it up.
May not make any difference on an anchor.

[rslifkin]

Originally Posted by svchances

Zinc is for salt or brackish water. Aluminium is for fresh water. Look it up.
May not make any difference on an anchor.

Aluminum anodes are also acceptable in salt or brackish water. The only material that's fresh water only is Magnesium (too active to use in anything more conductive than fresh water). And in really clean fresh water, Aluminum may not be active enough (but in many places it's fine).

[flightlead404]

Originally Posted by grantmc

Yes of course. Aluminium anodes (usually welded) are very common on things like lobster pots, why not anchors and chain too.

Aluminium or zinc? Most people have a preference, but for many that preference is based on the myth that because zinc anodes feel a lot heavier, they are therefore more effective. Not necessarily true - aluminium anodes are lighter, but that is actually one of several advantages they have over zinc. Obviously lighter anodes are easier to transport and handle, but – and here’s where it gets technical – the electro chemical capacity of aluminium is around three times higher than of the same mass of zinc, which means you get longer protection for less bulk. Aluminium anodes also have a relatively high driving voltage, so it has better distribution of the electrical current, compared to zinc. Another advantage of aluminium is that it doesn’t contain cadmium (zinc has a small amount) which is harmful to marine environments. Also, aluminium anodes are significantly cheaper than zinc for the same electro chemical capacity.

Yes, I've switched to AL for my shaft anodes for these reasons.