I don't have Anode; Do I need one?

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retsina

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I don\'t have Anode; Do I need one?

My boat does not have an anode and it appears that never had one fitted. No sign of corrosion on engine or propeller; however, the original prop shaft was made of bronge which i replaced this season with a stainless steel shaft.

Am I going to have any problems with corrosion now that i have change the shaft?. Do I need to fit an anode; where and how?
 
Re: I don\'t have Anode; Do I need one?

[ QUOTE ]
Am I going to have any problems with corrosion now that i have change the shaft

[/ QUOTE ] Possibly, possibly not.

Two options: suck it and see or fit a shaft anode as a precaution. It'll need replacing regularly though even if it is doing nothing useful.

If not possible to fit a shaft anode then a hull anode close as possible to the prop and shaft but it will need a good electrical connection to the shaft and prop. Usually done by bonding to the engine/gearbox and bridging the flexible coupling. An "Electro eliminator" is the most effective
 
Re: I don\'t have Anode; Do I need one?

Against most peoples advice I would say do not bridge any coupling etc.

My boat has anodes - but they are still the same as 10 yrs ago when I bought the boat. Nothing has eroded away ... one of my bonding leads is actually disconnected after new shaft / coupling etc. fitted. Fitter reckoned it was doing nothing - originally was connected to shaft seal bronze body.

IMHO too many people bond things and then create a circuit that is unnecessary.

Like my boat - if it has survived over 30 yrs like it ... why fuss with it now ?
 
Re: I don\'t have Anode; Do I need one?

[ QUOTE ]
IMHO too many people bond things and then create a circuit that is unnecessary.
Like my boat - if it has survived over 30 yrs like it ... why fuss with it now ?

[/ QUOTE ] If a hull anode is to be fitted to protect the stern gear then any flexible coupling must be bridged to complete the circuit. A circuit IS necessary. No circuit = no protection = no point in fitting the anode.
Now whether the protection is required may be another matter. Hence my opening comment.

It may have survived for 30 years without an anode, but that was with a bronze propshaft. Now it has a stainless steel prop shaft! Things are different. It may survive another 30 years without an anode or it may not.

Personally I think it will probably be OK. Hence my first option to "suck it and see"
but like countless others a shaft anode could be fitted, if space allows, as a precautionary measure. Nothing lost except of course for the regular cost a new anode.
 
Re: I don\'t have Anode; Do I need one?

VicS ... the 30 yrs survival is MY stainless shaft !! not his ....

My prop is original, shaft OK was replaced about 7-8 yrs ago - but original that came out was replaced because it had to be cut to remove - coupling was so seized it couldn't be separated. There has been no cathodic erosion in all those years on my boat basically because the 'circuit' was never made.

As to OP's boat - I have no idea how old it is - but if it's had a bronze shaft ? Then it may be an 'old'un' like mine ... (no disrespect intended)
 
Re: I don\'t have Anode; Do I need one?

[ QUOTE ]
There has been no cathodic erosion in all those years on my boat basically because the 'circuit' was never made

[/ QUOTE ] You are saying then that if the flexible coupling on your shaft had been bridged you would have suffered galvanic corrosion of the stern gear.

I look forward to a detailed scientific explanation of that.
 
Re: I don\'t have Anode; Do I need one?

But doesn't there have to be some kind of circuit for galvanic corrosion to be a risk in the first place? Either the two dissimilar metals are pysically joined, or very close together so that the electrolyte itself provides the circuit. If you over-correct a weak or non-existent circuit between dissimilar metals with another one, aren't you in danger of causing rather than preventing corrosion?.
 
Re: I don\'t have Anode; Do I need one?

Yes there has to be a circuit. One half of that circuit is through the electrolyte ( the water) the other is via the physical connection between the two metals (be that direct or via another path such as a deliberate wire connection)

If you have two dissimilar metals connected together electrically and immersed in the same electrolyte then corrosion will almost certainly occur of the more anodic or least "noble". Connect a piece of copper and a piece of iron together with a wire and immerse them both in seawater then the iron will corrode as a small electric current flows around the circuit.

Cathodic protection by means of a sacrificial anode is achieved by introducing a third metal which is less noble than either of the other two but connected to them It corrodes in preference to either of them as a result of reversing the current flow at the surface of the previously more anodic.

A bit more detail on the MGDuff website

and HERE on the National Physical Laboratory website
 
Re: I don\'t have Anode; Do I need one?

[ QUOTE ]
[ QUOTE ]
There has been no cathodic erosion in all those years on my boat basically because the 'circuit' was never made

[/ QUOTE ] You are saying then that if the flexible coupling on your shaft had been bridged you would have suffered galvanic corrosion of the stern gear.

I look forward to a detailed scientific explanation of that.

[/ QUOTE ]

Anodes are passive protection rather than impressed current active as used on ships. Boats usually are GRP or wood (we'll leave out metal based hulls as they will have to be bonded by default) - so we need to create a circuit to need anodes in effect.
If I grounded my VHF, GPS, mains and other items as some advise - then maybe I would see action on my anodes. But they are not for good reason. I do not wish to create a problem to be solved.
The boat has been like that since 75 when she was commissioned, and I don't see any reason to change.

Lets look at my shaft coupling ... probably the resistance across that without a bridging wire is enough to break serious circuit from prop to engine to cooling water back to sea. My prop shows no signs of erosion, no fittings show signs of erosion ... so why should I complain ?? I'm a happy boat-owner as I don't have to play with anodes !

Apply a few bridging cables, grounded items and I suspect I will then have to play anode game !

Now I'm gonna be bombed for not grounding out items on board ... I can't win !! /forums/images/graemlins/grin.gif /forums/images/graemlins/grin.gif /forums/images/graemlins/grin.gif /forums/images/graemlins/grin.gif
 
Re: I don\'t have Anode; Do I need one?

Not discussing VHF GPS or anything else except the prop and shaft.

You said, referring to bridging the coupling, "There has been no cathodic erosion in all those years on my boat basically because the 'circuit' was never made "

That implies that if the coupling had been bridged galvanic corrosion (corrosion not erosion, that's a mechanical process) would have been the inevitable result.

A detailed scientific explanation of that is still awaited. Description of the complete circuit, driving potentials and the electrochemical reactions occurring at the surfaces of the metal components involved.
 
Re: I don\'t have Anode; Do I need one?

Hey VicS are you on something ?? I take your posts as one of the real gents and good - but what is this waiting for scientific evidence stance now ?

If there's no evidence of need for anode on my boat - why should I worry about it ? If the prop is not eating away then why cure a non-existent problem ...

Corrosion / erosion - I don't really mind what it's called ... I have not a problem.

My stand continues ... most peoples woes come about because they bond gear and bridge items on board. Viola - Anode called for ...

So no science needed, no lab data required, simply my boat does not need to have anodes. They are there - but have been in similar condition for all the years I've had the boat - ~10.
 
Re: I don\'t have Anode; Do I need one?

I don't claim to understand the details of the physics of how this works but suffice it to say that we lost a prop to electolytic action 10 years ago when we had a perfect non-eroding anode. Now we have the same prop and anodes that erode since they were coupled.
 
Re: I don\'t have Anode; Do I need one?

I am not disputing that you have no problems of the galvanic variety or suggesting that after 30years you need to take steps to avoid any.

I am simply taking you to task for the statement which implied that if you had bridged the flexible coupling galvanic corrosion would have been the inevitable result. In isolation it would not have been! Any theories about what might happen have to be supportable by a reasoned scientific explanation.

Many people do I am quite sure fit anodes unnecessarily and many also probably start bonding things together that should not be bonded thereby creating problems that did not previously exist.
You say, "most peoples woes come about because they bond gear and bridge items on board." While I agree that may happen I suggest that "most" is an exaggeration.
In some cases people fit anodes, maybe to solve a corrosion problem, but fail to bond them properly to the items to be protected. Resulting in existing problem not being solved, not a problem created.

Many builders fit anodes as a precautionary measure. That's fine but of course means the owner then feels obliged to replace them regularly. Many are happy to stump up the cost of a small shaft anode periodically rather than risk prop or shaft failure.

Chris_E's post is interesting. He lost a prop despite having an anode fitted because, if I read his post correctly, the anode was not properly bonded to the stern gear. Now there may be reasons why his prop corroded that we do not now about, or it may have not have been of a good corrosion resistant material. Whatever the reason his subsequent experiences indicate that a correctly bonded anode prevents the trouble. Had he have stopped and wondered why his anode was not corroding then he might have identified the problem and saved the original prop. He wont make that mistake again!
 
Re: I don\'t have Anode; Do I need one?

Too bloody right! We now have an Autoprop that cost over four figures as opposed the £200 for initial replacement...

The Autoprop comes with its own anode at the shaft, this erodes as do the two others on the hull.
 
Re: I don\'t have Anode; Do I need one?

[ QUOTE ]
I am simply taking you to task for the statement which implied that if you had bridged the flexible coupling galvanic corrosion would have been the inevitable result. In isolation it would not have been! Any theories about what might happen have to be supportable by a reasoned scientific explanation.

[/ QUOTE ]

I wouldn't quite say categorically bridging WILL cause corrsion or depletion, I assume it will because I am now creating a circuit ... seawater inlet ... shaft ... prop to sea again. I then assume that anode would be connected to reduce possibility that my lovely prop doesn't dissolve away ...

Assume is a terrible word - but for want of a better one - it will suffice.

I don't argue with you VicS ... each boat has it's own quirks and needs.
 
Re: I don\'t have Anode; Do I need one?

A flexible coupling on its own may or may not provide electrical conductivity. If you need to fit a connecting wire in order to make the sacrificial anode work, that surely suggests that the coupling was not providing an electrical link in the first place? And if there was no link, then where was the necessary circuit for corrosion?
 
Re: I don\'t have Anode; Do I need one?

[ QUOTE ]
I am now creating a circuit ... seawater inlet ... shaft ... prop to sea again

[/ QUOTE ] But why do you have your seawater inlet bonded to the shaft?

Even if you do and the inlet seacock is close enough to the stern gear it is presumably also bronze and as a result there is still no threat yo your lovely prop.

Best advice with bronze seacocks is not to bond them to anything else.
 
Re: I don\'t have Anode; Do I need one?

Hi ,
Slightly different question but still anode related – I have recently fitted a galvanic isolator to protect my boats anodes whilst on shore power but even with that it seems my shaft and transom anodes are disappearing very very quickly ( I will be lucky if they last 3 months at this rate ) . The anodes fitted are McDuff zinc so quality shouldn’t be an issue.
Of course I would be really worried if my anodes weren’t wasting at all but the rate compared to another similar size boat sitting beside me at the Marina is startling.
Any ideas why ? is there anything I can do about it ?
 
Re: I don\'t have Anode; Do I need one?

[ QUOTE ]
A flexible coupling on its own may or may not provide electrical conductivity. If you need to fit a connecting wire in order to make the sacrificial anode work, that surely suggests that the coupling was not providing an electrical link in the first place? And if there was no link, then where was the necessary circuit for corrosion?

[/ QUOTE ]

Isn't that what I have been saying - in a diferent way ?
 
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