Is it possible to have too many anodes??

[tcm]

Changed the anodes and got the man to put on an isolation transformer ££ ugh.

My shaft anodes are not replaceable with scuba dive so i want to extend their life as long as poss...lifting the boat only possible in super-wide lifts.

So a hanging anode in adition to existing anodes becomes attractive when leaving boat for long periods in marinas.......but now as per question, a leetle frenchman in the pub last night told me maybe eet will be to murch anodes and ze reverse will hapen, hein? in other words, he indicated that too much anodery is as bad as too little. Is this bollox? Ithink it is. But dunno?

Any further info appreciated.

 

[ccscott49]

I have heard of "over anoding", but only on wooden boats, but I think it's bollox as well. So anybody with better knowledge, I'd be interested as well.

 

[lookout]

ahh, recently chatted to nice english man at anode-makers in Faversham- who backed up what I'd read before, that only issue was possibly gassing at the surface of the metal being protected- Chemists don't bust me - just reporting was was said/read.

Soo, with a painted steel boat & anodes hanging like bananas- maybe the bubbles push the badly applied paint off? ( some 'evidence' of this on mine, for sure ) but otherwise no probs.

Of course this time I bought bigger anodes thinking the 2kg ones only just manage 2 years afloat, and out the water find the old ones still very useable for another year if needed; but new ones went on anyhow, since expensive anodes actually aren't expensive at all when bought direct from the foundry here , super chaps even mod'd a standard unit with longer mountings & custom slots to fit the boat at no extra cost.

edit - yes, Englander, I'd read of it softening the timber around the anodes on woody boats

 

[Porthandbuoy]

[ QUOTE ]
edit - yes, Englander, I'd read of it softening the timber around the anodes on woody boats

[/ QUOTE ]

Er. I think it's around the noble metals you're trying to protect where the wood suffers.

 

[boatmike]

Absolutely. Really terrible to have too many anodes... It will seriously upset your stability, the area under the z curve will be affected and your boat will sink.

 

[paddywackcocker]

I think you would have to have an orfull lot out before any adverse effect was noticed if any. hanging one over the side may not draw away from the shaft ones, it will aways seek its shortest path, and in line of sight, so Me thinks your shaft ones still take the brunt of it, but ounce they become a bit sad the hanging one should take over bit by bit

 

[lookout]

well yes, quite possibly, or not, I have no idea which way round it was really, just that it went soft, ooer.

D'you know how that happens, in seriousness?

 

[Porthandbuoy]

[ QUOTE ]
well yes, quite possibly, or not, I have no idea which way round it was really, just that it went soft, ooer.

D'you know how that happens, in seriousness?

[/ QUOTE ]

I think it's electrochemical decomposition of the cellulose fibers, or the lignum cell walls, or both, or something entirely different. Er, don't know really.

Any chemists out there??? /forums/images/graemlins/confused.gif

 

[VicS]

[ QUOTE ]
Any chemists out there???

[/ QUOTE ] Well I still remember a little but you can read all about it in one of MGDuff's technical documents Here

I would object to the bit that says "In this process, known as “Hydrolysis”, water is ‘broken down’ into its component parts of hydrogen and oxygen. The liberation of hydrogen at the cathode results in an increased level of alkalinity

It is true that an increase in alkalinity (and pH) occurs but perhaps not quite by that mechanism.

 

[huldah]

Wow. I have two magnesium anodes hanging at the rear of the boat to protect the steel rudder. The lower bearing and frame are bolted into the oak keel.

Do I leave them or remove them?

Philip

 

[Porthandbuoy]

Dunno. Magnesium implies fresh water sailing, so no salt to complicate things (as if it wasn't complicated enough).

 

[huldah]

Re: Is it possible to have too many anodes?? [Re: Mariposa]

Thanks, I feel better already. Yes, you are right, she is moored in fresh water. I knew anodes are often not recommended for wooden boats, but I did not know how the damage occurred.

Philip

 

[Grajan]

Yes! paint films hate it when you over protect and miriads of blisters will form in the coatings going right back to the steel around anode(s)

 

[Grajan]

Re last post mainly in salt water but have seen it on vessels plying in fresh water especially if there is a power leak to the hull

 

[VicS]

[ QUOTE ]
Wow. I have two magnesium anodes hanging at the rear of the boat to protect the steel rudder. The lower bearing and frame are bolted into the oak keel.
Do I leave them or remove them?

[/ QUOTE ] Probably leave them but inspect the timber around the bottom bearing and frame. Remove them if any trouble is suspected.

How are your anodes connected to the rudder? Via the tiller or via the bearings. Is the connection really all that good?

I wonder if it would be better to fit anodes directly to the steel rudder. It would improve the protection of the rudder provided it did not lead to over protection lifting the paint off.

 

[Stoaty]

[ QUOTE ]
I would object to the bit that says "In this process, known as “Hydrolysis”, water is ‘broken down’ into its component parts of hydrogen and oxygen. The liberation of hydrogen at the cathode results in an increased level of alkalinity

[/ QUOTE ]

In practice the breaking down of <u>sea water</u> will also produce Chlorine and Sodium Hydroxide. Perhaps this is where the increased level of alkalinity comes from.

 

[boatmike]

How many anodes are there in an "orfull"?

 

[VicS]

[ QUOTE ]
In practice the breaking down of sea water will also produce Chlorine and Sodium Hydroxide

[/ QUOTE ] Precisely. The cations, sodium, calcium etc migrate towards the cathode (the items being protected) that leads to a rise in pH, (yes sodium hydroxide aka caustic soda is produced), the deposition of calcium carbonate and the release of a little hydrogen. The anions, sulphate, chloride etc migrate towards the anode. That leads to the release of oxygen and chlorine and a fall in pH and the dissolution of the anode. I'd expect very little free chlorine to be actually released and little oxygen either as the main result will be the dissolution of the anode.

 

[Stoaty]

I think you may be surprised about how much chlorine is given off. This reaction when sea water gets into the battery compartment of a submarine can incapacitate a crew very quickly.

PM me if you would like a simple home experiment to create your own chlorine and sodium hydroxide.

 

[VicS]

[ QUOTE ]
I think you may be surprised about how much chlorine is given off. This reaction when sea water gets into the battery compartment of a submarine can incapacitate a crew very quickly.

[/ QUOTE ] Oh I know that you can produce a lot of chlorine from salt water by electrolysis. I've done it often enough on a small scale. In fact a current of 1 amp will potentially produce 0.13 cc of chlorine gas per second (please free free to check my arithmetic though) However in the context of cathodic protection by sacrificial anodes the currents involved are very small and since chlorine is fairly soluble and the water is moving one would not expect free chlorine gas to be evolved, it would be swept away as a hypochlorite solution at the very least

Generally speaking though in electrolysis deposition or evolution of an element at an electrode is the last thing that is likely to happen after reacting with the electrode and reacting with the electrolyte. In the case of zinc electrodes they will be attacked to form zinc chloride and since sea water contains high concentrations of sulphates zinc sulphate will also be formed. These are basically the mechanisms by which metal is lost from sacrificial anodes.