Wiring a Zinc Anode to Aluminium

[haydude]

I have to protect a semi submerged Aluminium shaft using a Zinc anode to dip over the side.

The simplest installation, using materials that I have already, would be to use a copper wire linked to an existing stainless steel through deck fitting to which to attach a stainless steel wire with a s/s clip on one end and a bolted Zinc anode on the other end.

I am wondering, would this work, or using copper and s/s would nullify the zinc anode protection? I thought that ideally I should use an aluminium wire throughout, but this might mean having to drill holes because I do not have any existing through deck aluminium fitting nearby.

I would like to hear from our metallurgist Vyv Cox ...

Thank you in advance.

 

[KellysEye]

I think a mix of stainless, copper and zinc should produce a good current, exactly what you don't want. Zinc coated galvanised wire is available. I don't know what you do about the stainless though. ViV Cox should know.

 

[Dave_Seager]

I do not think that the materials matter unless they are immersed in the electrolyte (seawater).

 

[haydude]

I do not think that the materials matter unless they are immersed in the electrolyte (seawater).

The copper wire will not be immersed. Only the last short end of the s/s wire holding the zinc anode will be.

Vyv, please could you help?

 

[VicS]

the hanging anodes which MG Duff supply are on a 3m stainless steel wire..but the anodes are cast with the wire embedded in them rather than bolted on.

It would be wise to keep the number of joints to a minimum but there should be no problem connecting stainless steel to copper out of the water.
I'd be more concerned about the copper wire connecting to the aluminium shaft but provided the junction is kept dry there should not be a great problem.

How are you intending to make this connection ?

If you have aluminium cable available why not make the shaft to stainless steel section from it and so avoid any complications the copper might introduce.

 

[Quandary]

I think a mix of stainless, copper and zinc should produce a good current, exactly what you don't want. Zinc coated galvanised wire is available. I don't know what you do about the stainless though. ViV Cox should know.

Why would you not want a good current? would you prefer the current to find an easier path through the shaft. Nearly all manufactured (as distinct from home made) are lumps of zinc on the end of stainless steel wire, copper wire would be a better conductor, just not as durable.
Mine is copper to a stainless through bolt, then ss wire to the immersed anode, to protect an alloy saildrive leg. Works fine for me. I made one all copper cable to the lump of zinc., in theory it would have been more effective but the copper wire does not like to be bent frequently so has to be handled more carefully

 

[haydude]

If you have aluminium cable available why not make the shaft to stainless steel section from it and so avoid any complications the copper might introduce.

Thanks Vyv, much appreciated. I would rather prefer to use aluminium wire as you suggest, only I haven't found where to buy it, and I have plenty of copper wire available.

The connection will be either through a bolt and eye or soldered (if I can manage to solder copper on aluminium using an iron). Then I could actually pot the joint using the resin we have all learnt about building the jaycar kit.

 

[Quandary]

Lake sailored or worse?

 

[vyv_cox]

Thanks Vyv, much appreciated. I would rather prefer to use aluminium wire as you suggest, only I haven't found where to buy it, and I have plenty of copper wire available.

The connection will be either through a bolt and eye or soldered (if I can manage to solder copper on aluminium using an iron). Then I could actually pot the joint using the resin we have all learnt about building the jaycar kit.

It was VicS who replied, not me, although I have no problem with his response. Zinc is more electronegative than any of the metals you are considering, so it will protect all of them. For example, consider a typical zinc anode with mild steel fastenings on a stainless steel propshaft with a manganese bronze propeller. As has been suggested, if the aluminium to copper connection is wet there is a risk that the aluminium will be lost.

The 'rules' of Lakesailoring seem to have changed. I understood it to be as Quandary suggests above, but it now seems to mean repeating advice that has already been given further up the thread. That happens so often that it barely merits a mention.

 

[VicS]

I dont know what "lakesailoring" means. I have seen the rules... I did not read them.

BTW I always avoid the use of the terms electronegative and electropositive in the context of the galvanic series

Strictly electronegativity is the tendency to attract electrons, and form negative ions.

Electropositivity is the tendency to donate electrons, and form positive ions.

This is pretty much the opposite to the way you and many others use the terms in relation to the galvanic series and it is the more electropositive metals which are to be found with the more negative electrode potentials in the electrochemical and galvanic series.

Confused ? That's why I avoid the use of the terms.

 

[pvb]

Confused ? That's why I avoid the use of the terms.

Good idea, Vyv.

 

[Thistle]

Am I missing something or won't the aluminium corrode to protect the zinc - exactly the opposite to what you want? Wouldn't a magnesium anode be better?

 

[VicS]

Am I missing something or won't the aluminium corrode to protect the zinc - exactly the opposite to what you want? Wouldn't a magnesium anode be better?

No zinc anodes are used to protect saildrives and outboards

Magnesium is only suitable for use in fresh water. It is too reactive to use in salt water but if the OP is in fresh water he probably should use magnesium because zinc is not effective

 

[Thistle]

No zinc anodes are used to protect saildrives and outboards

Magnesium is only suitable for use in fresh water. It is too reactive to use in salt water but if the OP is in fresh water he probably should use magnesium because zinc is not effective

How does that all work?

 

[VicS]

How does that all work?

But zinc tends to be come passivated, presumably due to a oxide layer, in fresh water

 

[Thistle]

Thanks. Hadn't appreciated that alloying changed things.

 

[KellysEye]

>The copper wire will not be immersed. Only the last short end of the s/s wire holding the zinc anode will be.

Ali boats drop the anode to the depth of what they wish to potect, usually the propellor. Is the SS wire long enough to reach the middle of the shaft?

>Why would you not want a good current?

Sorry thay was not clear. If you mix metals in salt water it will create current as will a mix of salt and fresh water, such as in river mouths. The higher the current the quicker whatever is being potected will corrode.

Also stray current from a 240v supply in a marina will eat anodes very quickly. We saw a yacht in Portugal that had that and when he started the engine found that the prop had been eaten too.

 

[Quandary]

>The copper wire will not be immersed. Only the last short end of the s/s wire holding the zinc anode will be.

Ali boats drop the anode to the depth of what they wish to potect, usually the propellor. Is the SS wire long enough to reach the middle of the shaft?

>Why would you not want a good current?

Sorry thay was not clear. If you mix metals in salt water it will create current as will a mix of salt and fresh water, such as in river mouths. The higher the current the quicker whatever is being potected will corrode.

Also stray current from a 240v supply in a marina will eat anodes very quickly. We saw a yacht in Portugal that had that and when he started the engine found that the prop had been eaten too.

I hope I am the only one that can not grasp what you are telling us, so please be patient with me.
You may not want 'a good current' but you certainly need a good conductor linking the protected metal to the anode, this will be capable of carrying 'a good current'. If the major part is copper with the stainless wire restricted to the immersed point that will conduct OK, it should not corrode where the copper meets the stainless if there is no water present, in theory there is a risk where the stainless wire is buried in the zinc but in practice the zinc does the corroding. If you wanted to restrict the current between the shaft and the anode you would not use a conductor to link them but then the shaft would have no protection. Sea water, most brackish or even 'fresh' water is an effective electrolyte hence the need for anodes, stainless steel aluminium alloys and even bronze alloys can go very quickly if the anode protecting them is lost or depleted. If you can secure an immersed anode directly to a shaft or leg that gives best protection but if you have to use a remote (hanging) anode you want to link them with the most effective conductor you can find, using the most conductive metals in the cable.
So is my recollection of the physics I laboured over all those centuries ago correct, or has the senility become even more advanced.