Cretin of the century award - runaway winner. Or can you beat this?

A number above have referred to the need for anodes to "see" the item they are protecting (I take this to mean that they are electrically connected AND also in line of sight under water. Is this latter point necessarily so? Please explain? (to quote one of our former politicians when she had no idea what a question meant). Thanks Andrew
 
ripvan1 said:
Sorry Vyv, I meant battery terminal. My main question tho' is why are anodes placed on outside the hull?
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To protect metal parts also outside the hull. They need to be connected electrically to the anode and be able to 'see' the items being protected. Now seen as largely unnecessary if the parts are made from corrosion resistant materials.
 
Hi Vyv, I am not being pedantic here - I am genuinely trying to understand the "see" aspect (and don't forget I have an Al boat). Does this mean that, with an anode cone on a prop, the aft face of the blade is OK, and the forward face, which cannot "see" the anode, is not protected? I know it is, but doesn't the "see" need some explanation?
Or in my case, an anode on the centreline P bracket - will it protect the hull out of sight around the bilge? Andrew.
 
Electrons in water travel pretty much in straight lines. There are slight variations, particularly at high powers, but here we are talking very low voltages and currents. So yes, an anode would be very hard pressed to protect for example, a fitting around the curve of the hull. Aluminium boats that I have watched use several anodes all around the hull to overcome this. We once berthed next to 'War Baby', a very famous aluminium yacht, which was festooned with anodes on wires.

I guess that with a propeller the whole thing is in electrical contact so it would all be protected. Anodes on folding and feathering props are mostly there to protect against galvanic corrosion resulting from mixtures of copper based alloys and stainless steel pivot pins, for instance. A fixed prop may dezincify despite the presence of an anode, although having learned from VicS the other day that the aluminium alloy used for aluminium anodes is less noble than zinc it could be that this would be a better choice. Unfortunately I don't know where the zinc phase in brass, or the zinc alloy used for anodes, comes in the galvanic series.
 
Thanks Vyv, that it is sort of detail I was hoping for and I certainly defer to your knowledge and experience. Cheers, Andrew
(I should add that I'm happy to return to the OP's thread)
 
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Andrew G said:
Thanks Vyv, that it is sort of detail I was hoping for and I certainly defer to your knowledge and experience. Cheers, Andrew
(I should add that I'm happy to return to the OP's thread)
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No worries, mate! I'm flicking between anode stuff (again, again!) and cretin comments myself.

I still find the whole anode/bonding/corrosion theory somewhat confusing. I THINK I've established that Ph.Bronze seacocks don't need bonding/protecting but I haven't sussed-out if bonding them is actually harmful !!

I just hope some future owner of Khamsin doesn't rank something I have done to her as cretinous :hopeless:
 
Robert Wilson said:
I still find the whole anode/bonding/corrosion theory somewhat confusing. I THINK I've established that Ph.Bronze seacocks don't need bonding/protecting but I haven't sussed-out if bonding them is actually harmful !!
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Phosphor bronze is used for the bolts on Blakes seacocks, otherwise you are correct, bronze seacocks don't need any bonding or protection. There is a theoretical situation in which bonding could be harmful, if a bronze seacock was connected to a lesser alloy, also underwater. The lesser one would corrode preferentially to protect the bronze one. However, the reality is that most copper alloys occupy a similar position in the galvanic series, so the rate is not likely to be high. If you had an anode in the bonding circuit it would be corroded rapidly, whilst achieving nothing.
 
vyv_cox said:
Phosphor bronze is used for the bolts on Blakes seacocks, otherwise you are correct, bronze seacocks don't need any bonding or protection. There is a theoretical situation in which bonding could be harmful, if a bronze seacock was connected to a lesser alloy, also underwater. The lesser one would corrode preferentially to protect the bronze one. However, the reality is that most copper alloys occupy a similar position in the galvanic series, so the rate is not likely to be high. If you had an anode in the bonding circuit it would be corroded rapidly, whilst achieving nothing.
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Thank you Vyv.
I can now understand the process. I almost remember attending "galvanic series" lessons at skool, but sadly the theory and lessons have escaped over the years to some distant corner of my mind.

So, one bit less wiring to worry about in the nether regions of the boat!

And thanks to all of you who have posted.

Bye, f'now.

Robert W
 
vyv_cox said:
Electrons in water travel pretty much in straight lines.
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I wouldn't have thought that more than a minuscule proportions of the electrons leaving the cathode every got anywhere near the anode, what with slow diffusion speeds and all that. Is the potential distribution between electrodes ina fluid significantly difference from the potential distribution of any other conducting medium of the same shape?
 
JumbleDuck said:
I wouldn't have thought that more than a minuscule proportions of the electrons leaving the cathode every got anywhere near the anode, what with slow diffusion speeds and all that. Is the potential distribution between electrodes ina fluid significantly difference from the potential distribution of any other conducting medium of the same shape?
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Not my subject at all but I assume you are correct. It's all about driving energy I guess, those electrons are just desperate to complete the circuit.
 
vyv_cox said:
Not my subject at all but I assume you are correct. It's all about driving energy I guess, those electrons are just desperate to complete the circuit.
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It's not my field (ha-ha) either, though related to it. I'd have expected the volts per metre to be about the same for the same p.d. and shortest route, even if that had to go round a corner ... any electrochemists in the house?
 
vyv_cox said:
Not my subject at all but I assume you are correct. It's all about driving energy I guess, those electrons are just desperate to complete the circuit.
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JumbleDuck said:
It's not my field (ha-ha) either, though related to it. I'd have expected the volts per metre to be about the same for the same p.d. and shortest route, even if that had to go round a corner ... any electrochemists in the house?
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Not my subject either, but my wife is an doctor in electro-chemical engineering! I think that there is NO line of sight REQUIREMENT, but that as Vyv suggests, line of site paths are energetically favourable. Certainly electrons do not "flow" in the sense of an electric circuit; electrons are donated to the solution at the anode, and removed from the solution at the cathode. All that is required is an electron acceptor at the anode and an electron donor at the cathode; a complex solution like seawater should have no problem with that; plenty of anions and cations present in such a strongly polar solution.

The existence of batteries like the Leclanche and Bunsen cells (where anode and cathode are separated by a porous ceramic membrane) shows that "line of sight" connectivity is not required. The old-fashioned zinc/carbon dry batteries work the same way. Basically, your anode makes a simple primary cell with the metal being protected, and works in exactly the same way as these cells do. Distance from the anode may be an issue, but line of sight shouldn't be.

If I remember I'll check all this with my wife, but I'd be surprised if I was far wrong.
 
AntarcticPilot said:
Certainly electrons do not "flow" in the sense of an electric circuit; electrons are donated to the solution at the anode, and removed from the solution at the cathode.
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An over-enthusiastic pedant writes ...

They don't flow in an electric circuit either: there is just a gentle drift in the sea of valence electrons in the metal, with some being supplied at one end and some being removed at the other, very much as happens in an electrolyte. The energy is actually carried in the surrounding electric and magnetic fields, not in the electrons. Modelling those magnetic fields is my thing.

(Not contradicting, just climbing on a hobby horse)
 
Robert Wilson said:
Three of four Ph.Bronze through-hull retaining bolts for seacock sheared within the hull then the nuts and end bit of bolts glued (sikaflex?) back in place on the internal flange - presumably to make the seacock LOOK normal for survey/inspection.
The seacock is for the port-side cockpit drain, located very awkwardly behind the engine in very cramped space.
Luckily, during total re-wiring, and hence fitting new bonding wire to the seacock we found that one of the nuts plus end of bolt just fell off. We checked the other three and only one was intact.

Who would be so cretinous? I have no idea how long ago the crime was perpetrated or who by, but a very full inspection of all the other through hull fittings is in progress........

P.S. Finding replacement Ph.Bronze coach bolts is a nightmare. Eventually found Classic Marine on the web. A very helpful and pleasant guy can supply (£9+ each.....). If anyone has an alternative supply I'd be pleased to have a note of it for future reference.
Ta
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Most likely a yard botch!!
Cretin - well I don't know, the punter paid his bill I expect.
 
charles_reed said:
Most likely a yard botch!!
Cretin - well I don't know, the punter paid his bill I expect.
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At least someone is still on my OP :encouragement:

The boat was put together in part by two initial owners, then "finished" by a yard somewhere near Chichester. Difficult to trace any possible blame there. Assuming the seacocks have never been serviced, judging from their "less than perfect" condition and given her age I would guess it's been done sometime in her middle years (1980s/90s).

Fascinating as it is to read the above posts regarding electrons, anions, cations, dog-irons!!, Bunsen, Leclanche etc etc etc, I am totally lost-off. But don't let that put you off:encouragement:
 
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