Anodes who needs 'em!

[Tranona]

My last boat was moored on a remote mooring & the keel bolt I drew out went from over an inch diameter down to nothing in less than ten years.I don't know if that was electrolytic action but it sure as hell was alarming.(I had had the keel off 7/8 years previously so was able to check the condition.When I went to nip up the keel bolts last year as a matter of routine.The spanner just revolved at the slightest pressure & I drew out the stub about 4" long)

The problem with your iron bolt was probably not galvanic - just straightforward rust iron/steel in damp conditions. Particularly bad where a bolt passes through a wooden keel.

The anodes on your new boat are probably a complete waste of time. If they ar iron keels they will corrode, either because the surface treatment fails and/or impurities in the casting cause pockets of rust to form. There is no chance of galvanic corrosion as there are no dissimilar metals together.

Crevice corrosion in stainless steel is an entirely different phenomenom and is caused by oxygen exclusion. Most common in threads of bolts or where a bolt passes through damp wood. An anode will do nothing to stop this. Stainless is widely used for keel bolts in GRP boats because if the sealant used in the hull/keel interface is good, they never get wet. The have the advantage of not corroding on the surface in wet bilges unlike mild steel keel bots or nuts.

 

[Nicholas123]

The problem with your iron bolt was probably not galvanic - just straightforward rust iron/steel in damp conditions. Particularly bad where a bolt passes through a wooden keel.

The anodes on your new boat are probably a complete waste of time. If they ar iron keels they will corrode, either because the surface treatment fails and/or impurities in the casting cause pockets of rust to form. There is no chance of galvanic corrosion as there are no dissimilar metals together.

Crevice corrosion in stainless steel is an entirely different phenomenom and is caused by oxygen exclusion. Most common in threads of bolts or where a bolt passes through damp wood. An anode will do nothing to stop this. Stainless is widely used for keel bolts in GRP boats because if the sealant used in the hull/keel interface is good, they never get wet. The have the advantage of not corroding on the surface in wet bilges unlike mild steel keel bots or nuts.

That all sounds pretty accurate to me except if you had crevice corrosion caused by the ingress of sea water would'nt it also incite electrolytic action between the two dissimilar metals of stainless steel & cast iron?Ah the joys of boat ownership!

 

[Robert Wilson]

Dear VicS.
Thank you for that advice/comment. I am due to have my three year survey this winter, hopefully Ian Nicholson will be doing it. I shall seek his opinion on the subject, but yours seems to make very good sense.
I pretty sure Ian will condemn the wiring in any case, as much of it has been put in by previous owners in a random/ad hoc way. Also with very Heath Robinson connections and joins.
"Come the revolution" I'm going to have her totally rewired (The boat, not SWMBO)
My seacocks all seem to be in good condition, a couple with a build up of "green coating" but I'm not sure if that is ok, or bad.
My expertise in wiring, electricity, cathodic-protection is limited to basic one-way switching/positive+negative+earth (almost Red, black & bare!!). So any and all advice is welcome.
Thanks again.

 

[Paul DOUGOUT]

Well the question is do I need them?

My Macwester 27 has anodes fitted to the bottom leading edge of the keels & the trailing edge but one that is Identical (same mark) that I was looking at yesterday has not.So what is the criteria that causes you to need them?

Well a new engine is about £2000 reconditioned. Without anode connected the electrolysis eats the engine inside to out. I know! For the price Id have anodes AND make sure they are connected. I found the end tags corrode , not the cables or the anode if not connected. Its now a yearly inspection for me. Also your anchor chain will corrode if not diverted to a sacrificial anode. The clue is "sacrificial ", the result is £££££ or $$$$$$.

PS another bit of advice I was given was connect anode to keel bolts as well if metal keels. Its a back up. Also you can test earthing , its on here somewhere ?
Thanks to Eric , Steve and Chris for support in my engine change as a result of electrolysis and no anodes connected.

 

[Tranona]

Well a new engine is about £2000 reconditioned. Without anode connected the electrolysis eats the engine inside to out. I know! For the price Id have anodes AND make sure they are connected. I found the end tags corrode , not the cables or the anode if not connected. Its now a yearly inspection for me. Also your anchor chain will corrode if not diverted to a sacrificial anode. The clue is "sacrificial ", the result is £££££ or $$$$$$.

PS another bit of advice I was given was connect anode to keel bolts as well if metal keels. Its a back up. Also you can test earthing , its on here somewhere ?
Thanks to Eric , Steve and Chris for support in my engine change as a result of electrolysis and no anodes connected.

WElcome.

Please, please remove any connection between an anode and the engine UNLESS it is to connect to the propeller. do not connect your chain to anything. Engines may require nodes, but they will be in the cooling system NOT connected to outside the boat.

You have a serious misunderstanding of the process of galvanic action in relation to boats and their engines and the use of anodes to reduce the impact.

 

[VicS]

Well a new engine is about £2000 reconditioned. Without anode connected the electrolysis eats the engine inside to out. I know! For the price Id have anodes AND make sure they are connected. I found the end tags corrode , not the cables or the anode if not connected. Its now a yearly inspection for me. Also your anchor chain will corrode if not diverted to a sacrificial anode. The clue is "sacrificial ", the result is £££££ or $$$$$$.

PS another bit of advice I was given was connect anode to keel bolts as well if metal keels. Its a back up. Also you can test earthing , its on here somewhere ?
Thanks to Eric , Steve and Chris for support in my engine change as a result of electrolysis and no anodes connected.

This is an 11 year old thread.
In any case engine anodes is a different matter to anodes on keels etc

I would not have though that anodes to protect an anchor chain was a practical proposition. What do you do, fit one every metre or so to the chain?

Electrolysis is usually taken to mean corrosion driven by a power source, eg the 12 system, rather than by dissimilar metals. It is much more serious and can destroy things very quickly. It will not be prevented by sacrificial anodes

 

[Paul DOUGOUT]

WElcome.

Please, please remove any connection between an anode and the engine UNLESS it is to connect to the propeller. do not connect your chain to anything. Engines may require nodes, but they will be in the cooling system NOT connected to outside the boat.

You have a serious misunderstanding of the process of galvanic action in relation to boats and their engines and the use of anodes to reduce the impact.

I think you have a serious misunderstanding of what I said. I do not want this to be an issue. However, If there is no anode in my set up the salt water in the engine acts as a route to earth, in my case via ( through) the pump and timing chain cover. A prop is metalically connected to an engine in most boats unless you have a plastic or rubber section in the final drive.

The Volvo Penta D1=20 has no mixed metals in the HX and there is no part as an engine anode. I think like all things you need what you need for what you actually have. One size does not fit all.

IF there is no anode connected, the earthing can go down a wet mooring line to an anchor chain. I did not suggest this is a good idea more a very bad idea. The chain can erode by electrolysis.

That is my understanding from people who are clearly well qualified. I'll leave it there. You may have other understanding and you've expressed it. Thank you, Caveat emptor as the Romans and lawyers say.

 

[vyv_cox]

I think you have a serious misunderstanding of what I said. I do not want this to be an issue. However, If there is no anode in my set up the salt water in the engine acts as a route to earth, in my case via ( through) the pump and timing chain cover. A prop is metalically connected to an engine in most boats unless you have a plastic or rubber section in the final drive.

The Volvo Penta D1=20 has no mixed metals in the HX and there is no part as an engine anode. I think like all things you need what you need for what you actually have. One size does not fit all.

IF there is no anode connected, the earthing can go down a wet mooring line to an anchor chain. I did not suggest this is a good idea more a very bad idea. The chain can erode by electrolysis.

That is my understanding from people who are clearly well qualified. I'll leave it there. You may have other understanding and you've expressed it. Thank you, Caveat emptor as the Romans and lawyers say.

Having studied the topic extensively, based upon my qualification in metallurgy, I can say that I have never heard of anybody adding an anode to an anchor chain. The function of galvanising is to provide anodic protection to the steel.

 

[Tranona]

I think you have a serious misunderstanding of what I said. I do not want this to be an issue. However, If there is no anode in my set up the salt water in the engine acts as a route to earth, in my case via ( through) the pump and timing chain cover. A prop is metalically connected to an engine in most boats unless you have a plastic or rubber section in the final drive.

The Volvo Penta D1=20 has no mixed metals in the HX and there is no part as an engine anode. I think like all things you need what you need for what you actually have. One size does not fit all.

IF there is no anode connected, the earthing can go down a wet mooring line to an anchor chain. I did not suggest this is a good idea more a very bad idea. The chain can erode by electrolysis.

That is my understanding from people who are clearly well qualified. I'll leave it there. You may have other understanding and you've expressed it. Thank you, Caveat emptor as the Romans and lawyers say.

This is entirely new ideas that you have . While the propeller is often connected to the engine through the prop shaft, the engine is not in the same seawater as the propeller. For there to be a galvanic circuit the 2 metals must be in contact and submerged in an electrolyte. in this case seawater. So only the propeller and the shaft it is attached to fulfil this criterion. The anode works because it is both connect to the 2 metals AND in the same seawater plus the propeller must be able to "see" it. That is why it is usually directly connected (such as a shaft anode) or placed close by on the hull. the anode has a lower potential than the propeller so erodes in preference. This is nothing to do with the seawater in the engine.

The engine is not "earthed" to the seawater in the way that you suggest nor can anything "electric" flow through the seawater. That is why I said you have a serious misunderstanding of the principles. As vyv says same with your idea that anything can go down a wet mooring rope to the chain. Galvanising with zinc is there to protect the steel. Eventually it wears off, usually through abrasion and then the steel rusts. Nothing to do with galvanic action or electrolysis.

 

[VicS]

Having studied the topic extensively, based upon my qualification in metallurgy, I can say that I have never heard of anybody adding an anode to an anchor chain. The function of galvanising is to provide anodic protection to the steel.

• I think you mean cathodic protection .

 

[vyv_cox]

• I think you mean cathodic protection .

Well yes, I suppose you are correct. I only meant that the galvanising is the anode.

 

[Paul DOUGOUT]

• I think you mean cathodic protection .

Nobody is suggesting adding to an anchor chain. It can "short" to it without a good path, that's all. I'm not adding to this, its going round in circles.
Clearly I am not putting it in a way that you follow. Sorry, over and out.

 

[fisherman]

Thing is, it can depend. In Newlyn my anodes would disappear overwinter. In Porthleven they lasted for years.
I'm told it's welding work on nearby steel boats without earthing them first.
I would suggest that if your anodes are correctly bonded, (and even McDuff, the makers, used to be cagey about what exactly that entailed) then if they disappear you need them, and if they don't then money saved.
Mine were bonded to everything inc the gunmetal seacocks, and the shaft coupling was bridged. R&D used to put a connector like a pan scrubber between the two steel bars, I fitted a small bolt across. The keel band and steel rudder had their own anodes.
(The Mcduff site says "Do not bond the same anode to ferrous and non-ferrous metals or stainless steel." Then shows a pic of the wiring between engine, gearbox, shaft, prop, rudder, to the same anode. Hmmm)
Big boats with little downtime would change the lot whenever they dried out up the harbour, you could pick loads up part worn. Since I was in a drying harbour I could easily keep an eye.

 

[Tranona]

(The Mcduff site says "Do not bond the same anode to ferrous and non-ferrous metals or stainless steel." Then shows a pic of the wiring between engine, gearbox, shaft, prop, rudder, to the same anode. Hmmm)

They mean in the water. So a steel rudder should have its own anode. The anode connected to the shaft via the gearbox is to protect the prop from the stainless shaft.

 

[fisherman]

Having studied the topic extensively, based upon my qualification in metallurgy, I can say that I have never heard of anybody adding an anode to an anchor chain. The function of galvanising is to provide anodic protection to the steel.

I have, but to a mooring chain at Mylor, and they swore blind that the galv on the chain lasted much longer.

 

[vyv_cox]

I have, but to a mooring chain at Mylor, and they swore blind that the galv on the chain lasted much longer.

Yes, a mooring is different as it is immersed 365 days per year . Ours had zinc cast into the joint just below the swivel. Chain is not a great conductor of electricity so it probably did little more than a couple of metres away but every little helps. Ours only ever used black steel chain though.

 

[rogerthebodger]

They mean in the water. So a steel rudder should have its own anode. The anode connected to the shaft via the gearbox is to protect the prop from the stainless shaft.

Anode is a complex subject and I would not contradict Vyv_cox as I am just a simple Mechanical /Electrical Engineer,

My steel boat has quite extensive anodes and where stainless steel and mild steel are welded under water si in my MS rudder and SS rudder shaft. MS hull and SS skin fittings

For cathodic corrosion you need 4 factors . 2 differently metals and electric and an electrical commotion

My prop shaft and my propelled are both stainless steel so in theory I should not .need a shaft anode but I do .

My hull anodes do show little erosion in the 10 years I have been afloat

 

[ducked]

Having studied the topic extensively, based upon my qualification in metallurgy, I can say that I have never heard of anybody adding an anode to an anchor chain. The function of galvanising is to provide anodic protection to the steel.

I've heard it mentioned for fixed mooring protection, I think on Aberlady Bay yacht club website, but it might have been on another of the Firth of Forth club websites.

 

[Refueler]

When my engine was changed on my Sunrider25 ... the engineer remarked that the bonding wires I had (fitted by previous owners) were not doing anything and asked if I wanted them fitted ... I said forget it ..

That was near 20yrs ago ... any corrosion or signs of mistake ? None at all ... Shaft - prop - seacocks ... everything fine. The anodes that were left on the hull stayed same for years until finally started to fall off due to the fastenings corroded.

As another says - one can create a problem by bonding all together and just one connection error .....

IMHO - if each item is basically electrically isolated - then why should it be a problem. Environmental corrosion cannot be stopped - but electrical based can be.

My 38ft Conqubin has bonding wires across the keel bolt tops ... as to any others ?? I may one day search out and see what else there are .. but so far I cannot recall any anodes .... will have a good look again when I get back home from Dubai ...

 

[Tranona]

My 38ft Conqubin has bonding wires across the keel bolt tops ... as to any others ?? I may one day search out and see what else there are .. but so far I cannot recall any anodes .... will have a good look again when I get back home from Dubai ...

You may well find that the mast is also bonded to the keel as a path to earth for lightning protection.