Old used anodes, re-use???

[bammylovechops]

Hi,

I have seen a few boats with wire/cable dangling from them, when I have looked into the water I have seen old partially worn anodes attached to the cable and submerged in the water. I guess it's something to do with protecting the new anodes.
The queries I have are, where are they connected to at the other end of the cable? To the negative battery terminal perhaps? Or to metal work elsewhere?Secondly, how does this interfere/effect the galvanic isolator that I have?
My boat is a Sealine S28.
Any thoughts??????????

 

[VicS]

Hi,

I have seen a few boats with wire/cable dangling from them, when I have looked into the water I have seen old partially worn anodes attached to the cable and submerged in the water. I guess it's something to do with protecting the new anodes.
The queries I have are, where are they connected to at the other end of the cable? To the negative battery terminal perhaps? Or to metal work elsewhere?Secondly, how does this interfere/effect the galvanic isolator that I have?
My boat is a Sealine S28.
Any thoughts??????????

Depends to some extent how the boat is wired.

Connect them directly to items to protect if possible eg to drive legs. To the prop shaft to protect a shaft driven prop.

Other wise to the same wiring as the fixed anodes.

If the DC system is isolated the battery negative is not appropriate.
In any case not to any wiring that will actually be carrying current.

No problem regarding the GI. That should be in the incoming shorepower earth wire

 

[Cloven]

I have hanging anodes on my boat. The situation I am in is that the boat is moored in freshwater but we sail at sea. In freshwater, a Zinc anode soon becomes ineffective and the best option is a Magnesium anode. However, a Mg anode attached to the boat would disappear in days when at sea.

The compromise is to have Aluminium hull & shaft anodes attached to the boat. When moored in freshwater we use a hanging Mg anode and when moored in salt water a hanging Zinc anode. The anode wire is connected, via a through bolt on the transom, internally to the Al hull anode, engine, P bracket etc.

This set-up seems to work well. The Al anodes last for several seasons. The Mg anode (bought from a narrowboat chandlers) is till going strong after 5 seasons. The hanging Zn anode is hardly eroded at all probably because it only gets an outing when we are at anchor/on a mooring at sea.

Many AWB's also have this arrangement but the main use of hanging anodes is on the Aluminium hulled boats that are also in the marina. These tend to have multiple hanging anodes.

 

[Momac]

I can see the magnesium anode idea working in fesh water. The magnesium being more reactive will protect the alloy anodes.

But the zinc anode is less reactive than the alloy anodes. So I think the idea of suspending a zinc anode in salt water doesnt work. The alloy anodes will corrode and protect the zinc.

I think magnesium anodes would survive up to two years if you have no more than a week in brackish/salt water and the remainder in fresh water. Two weeks in salt water might see the magnesium fizz to nothing so alloy would be the answer.

Alloy anodes in fresh water may need a clean up now and again as they corrode slowly and a coat of corrosion can develop which inhibits the protective affect.


No expert - just stuff I have read and a bit of experience thrown in.

 

[bammylovechops]

Hi,

For info my boat is kept permanently in salt water and the boats I see with anodes dangling are also appear to be a long turn basis.

 

[vyv_cox]

But the zinc anode is less reactive than the alloy anodes. So I think the idea of suspending a zinc anode in salt water doesnt work. The alloy anodes will corrode and protect the zinc.
.

Not according to the galvanic series in seawater, example here. Zinc is more reactive than aluminium.

Why do you (and many others) say 'alloy' when you mean aluminium? An alloy is a mixture of two or more elements, mostly in solid solution. So virtually every metal in common use is an alloy, steel, brass, bronze, even zinc anodes, which are not usually the pure metal.

 

[GrumpyOldGit]

Ok vyv, most say Alloy meaning ALLY. A common misspronunciation like pacific instead of specific.
Bottom line is, bung a large lump of ally/ mag over the side on a bonding wire and attach the end to propshaft or leg or anything else you want to protect and leave well alone !

 

[VicS]

Aluminium anodes are usually made of an alloy which crucially contains a small amount of Indium.

There is very little difference in the potential of the Al/In alloy and zinc

 

[vyv_cox]

Ok vyv, most say Alloy meaning ALLY. A common misspronunciation like pacific instead of specific.

I'm not sure you are right. Cars are almost always described as having 'alloy wheels' when they think they mean aluminium, although there is a lot more in them than pure metal. For example, see here. Not a mention of aluminium or Ally.

 

[Stu Jackson]

I have hanging anodes on my boat. The situation I am in is that the boat is moored in freshwater but we sail at sea. ...

This set-up seems to work well. The Al anodes last for several seasons. The Mg anode (bought from a narrowboat chandlers) is till going strong after 5 seasons. The hanging Zn anode is hardly eroded at all probably because it only gets an outing when we are at anchor/on a mooring at sea.

Have you considered that your anodes don't disappear is because you are on a mooring and thus not susceptible to stray currents that one would find in a marina where so many boats are plugged in all the time?

 

[Momac]

Not according to the galvanic series in seawater, example here. Zinc is more reactive than aluminium.

Why do you (and many others) say 'alloy' when you mean aluminium? An alloy is a mixture of two or more elements, mostly in solid solution. So virtually every metal in common use is an alloy, steel, brass, bronze, even zinc anodes, which are not usually the pure metal.

I wrote 'alloy' as I think such anodes are not necessarily pure aluminium therefore should I should have written 'aluminium alloy'.
'Aluminium Alloy Anodes' is a bit of a mouthful even when writing it !

In fact the chart on your link refers to aluminium alloy - whatever that is.

Surprising the 'aluminium alloy anodes' don't sit somewhere where between magnesium and zinc. If I'm wrong thats fine .

Does the following the following help
http://www.westcoastanodes.co.uk/Boat_Anodes/ANODES_AND_GALVANIC_CORROSION.html

 

[vyv_cox]

In fact the chart on your link refers to aluminium alloy - whatever that is.

It says 'aluminium alloys', not aluminium alloy. There is a subtle difference that explains why the voltage range is relatively large. Pure aluminium is not used for anything that I'm aware of, it is alloyed with many other metals to give the desired properties for the application.

 

[IanP]

I learn something new here every day. When I saw the word ally in a post, I thought the poster had missed an o in the spelling.
I'm sure Vyv must be technically correct. But I and everyone that I know would describe an alluminium alloy fitting as an alloy fitting . In the case of alloy wheels, wikipedia here describe them as mostly an alloy of aluminium and magnesium. Should we then describe them as ally wheels? I'm going to stick with alloy.
P.S. I still call my hoover a hoover, even though its a nilfisk.

 

[vyv_cox]

It's just a particular gripe of mine. Why pick on aluminium alloys as 'alloy' when every metal article we use, from gold jewellery to cantilever bridges, is also an alloy? I even know of some plastics that are described by their manufacturers as 'alloys', although I think that may be stretching things a bit far as they are obviously mixtures.

 

[LadyInBed]

In the case of alloy wheels, wikipedia here describe them as mostly an alloy of aluminium and magnesium. Should we then describe them as ally wheels? I'm going to stick with alloy.

In my youth we used to call the Mag-ally wheels

 

[nigelmercier]

I have looked into the water I have seen old partially worn anodes attached to the cable ... where are they connected to at the other end of the cable? ...

Connect to the same place as your other anodes, battery negative or shunt. I regularly melt down a bunch of old anodes and make a small fender shape for this purpose.

 

[nedmin]

Not good practice to use magnesium anodes on a steel cruiser hull, especially if the waters a bit brackish as they can fetch the paint off.I know narrow boats use them but I wouldnt.Ally is much better.

 

[bammylovechops]

Connect to the same place as your other anodes, battery negative or shunt. I regularly melt down a bunch of old anodes and make a small fender shape for this purpose.

Thanks for putting the thread back on track

 

[maby]

Hi,

For info my boat is kept permanently in salt water and the boats I see with anodes dangling are also appear to be a long turn basis.

There is still a merit in dangling auxilliary anodes even if you are permanently in salt water, specially if you are on shore-power much of the time. It simply helps to extend the life of your fixed anode(s) - which are difficult to change without hauling the boat out. I've found my primary anodes significantly eroded at the end of the season and it can be hard to be sure just how much is left. It costs little to dangle an extra anode over the side and undoubtedly reduces the rate of erosion of the fixed anodes - so why not do it?

Just don't make the mistake of buying a purpose built auxilliary anode - they cost three or four times the price of an equivalent fixed anode - it's very easy to solder a length of medium thickness wire onto a bar anode and save a fortune.

 

[bammylovechops]

There is still a merit in dangling auxilliary anodes even if you are permanently in salt water, specially if you are on shore-power much of the time. It simply helps to extend the life of your fixed anode(s) - which are difficult to change without hauling the boat out. I've found my primary anodes significantly eroded at the end of the season and it can be hard to be sure just how much is left. It costs little to dangle an extra anode over the side and undoubtedly reduces the rate of erosion of the ixed anodes - so why not do it?

Just don't make the mistake of buying a purpose built auxilliary anode - they cost three or four times the price of an equivalent fixed anode - it's very easy to solder a length of medium thickness wire onto a bar anode and save a fortune.

Hi maby,
Where do you connect the other end to?
Mark