Barnacles causing bronze prop electrolysis....?

[VicS]

Calcium is a chemical element with symbol Ca and atomic number 20. An alkaline earth metal. Dissimilar metals will cause corrosion as will stray current. A galvanic isolator will stop stray current but not dissimilar metal corrosion.

And the relevance to these facts about calcium is what exactly?

A galvanic isolator will stop currents originating from very low voltage sources, such as dissimilar metals, conducted by the shorepower earth connection from causing corrosion. It will not stop currents originating from higher voltage sources such as a 12 volt system.

 

[RichardS]

Calcium is a chemical element with symbol Ca and atomic number 20. An alkaline earth metal.

And the relevance to these facts about calcium is what exactly?

The metallic Calcium produced by the barnacles also instantaneously reacts vigorously with seawater to produce copious quantities of hydrogen gas.

Which is why wherever you find barnacles you will inevitably observe humungous spontaneous explosions which nearly always result in severed body parts.

Richard

 

[Hydrozoan]

Thanks Hydrozoan, I am afraid it's just my limited photography skills giving an impression of whitish deposits, in fact it's all now polished bronze, don't think there were any deposits before polishing either. Your point about barnacles cement complexing copper is very interesting, sounds like that's what is happening.

My pleasure, and my sincere apologies for the implied suggestion that your cleaning prior to polishing might have been inadequate - though it does indeed look mostly white-ish, and in places raised above the pink spots, on my screen. At least I said my impression might be incorrect!

Yes, a complexing agent like a protein in solution could in principle bind with copper (itself the most strongly complexing of the first series transition metals) and thus aid its dissolution from bronze, but I was cautious about that in your case because I presume that the ‘cement’ sets and that the barnacles stay stuck down in one place. But as Flica’s experience confirms your own, perhaps the cement both complexes some copper and gradually dissolves away carrying the copper with it, getting replaced by new cement as the barnacle grows. I do recall reading somewhere that the cement composition may be different between first larval settlement and later, and have since also found this abstract of a paper which suggests that the stuff can etch 316L stainless steel.
http://www.sciencedirect.com/science/article/pii/S0927776510002481

Fascinating though barnacles and their cement may be, I hope that your ‘craters’ polish out as easily as Flica’s do.

 

[lpdsn]

Like fig 2 below ?

Yes.

There's only one complication. The calorifier heating element is disconnected at the moment (to be honest has been since I bought the boat) so when I replace that there will be the risk of a connection between the earthed heating element and the engine block via the cooling water so I may well end up putting the earth for the heating element o the 'isolated' side of the GI. There's no connection between anything else connected to the mains circuits that risks leakage to DC ground under normal circumstances.

 

[lpdsn]

Which is why wherever you find barnacles you will inevitably observe humungous spontaneous explosions which nearly always result in severed body parts.

Richard

If only. It could form the basis of a new type of self-eroding antifoul.

I can see the marketing literature now. "Go on Barnacle, make my day!"

 

[KellysEye]

>A galvanic isolator will stop currents originating from very low voltage sources, such as dissimilar metals, conducted by the shorepower earth connection from causing corrosion. It will not stop currents originating from higher voltage sources such as a 12 volt system.

We had a galvanic isolator on both our 12v and 240v earth wires.

When you plug into mains shore power the cable you use has 3 internal cables: A live, a neutral & an earth wire. The earth wire goes to the shore power pedestal where it is physically connected to the ground. This is a safety wire and protects you in the case of an electrical problem.

Your neighbouring boats also use the same earth connection. This effectively connects all the boats together via the earth cables in the shore power leads. In your boat the shore power earth lead goes to your electrical consumer unit & then to all metal components such as the engine block, fuel tanks, shafts/ propellers etc & then finally connects to your anodes. unfortunately as all the boats (and metal pontoons) are now interconnected via the earth cables any voltage leaks or "galvanically" generated voltages have an easy path between the boats. This often results in rapid loss of sacrificial anodes & increased corrosion of all underwater metals. If the boat next to you does not have anodes he won't worry: He is using yours!

 

[lpdsn]

A galvanic isolator will stop currents originating from very low voltage sources, such as dissimilar metals, conducted by the shorepower earth connection from causing corrosion. It will not stop currents originating from higher voltage sources such as a 12 volt system.

Very much so. My GI came with a couple of warning LEDs* which helped me spot it when a nearby large MoBo was using my earth to earth their 24V system via its props. Marina contacted the owner and he'd turned the power off by the time I went back a few days later, but I later saw his props in the yard. They'd lost a large amount of metal so it must've cost him a fortune for two new ones.

 

[lpdsn]

The earth wire goes to the shore power pedestal where it is physically connected to the ground.

Not quite. It is earthed back on land. For a large marina that could be significant distance. I jokingly tell crew when they get to the marina office that there's only another quarter of a mile to go, but it will be something around that distance. That's a long earth wire and the protection provided is much less than you'd get in any properly wired building.

PS Can you draw up the circuit around your GI farm? I'm having difficulty visualising what you've done.

 

[RichardS]

We had a galvanic isolator on both our 12v and 240v earth wires.

I can't understand that. Assuming that there is only one earth connection going from the boat to the shore then any extraneous currents which you are hoping to block, in either direction, must be going along that cable. How would a GI on the 12V system, which can only connect to earth through that same cable, achieve anything?

Richard

 

[PaulRainbow]

I can't understand that. Assuming that there is only one earth connection going from the boat to the shore then any extraneous currents which you are hoping to block, in either direction, must be going along that cable. How would a GI on the 12V system, which can only connect to earth through that same cable, achieve anything?

Richard

I suspect he means both the 12v and 240v circuits were connected to the GI, version 1 of the diagrams Vic posted.

 

[VicS]

I suspect he means both the 12v and 240v circuits were connected to the GI, version 1 of the diagrams Vic posted.

No. He has told us before that he had two GI's. One on the 12 volt system and one on the 240 volt system.

 

[PaulRainbow]

No. He has told us before that he had two GI's. One on the 12 volt system and one on the 240 volt system.

I don't suppose i should be surprised lol

I'm a bit puzzled by the diagrams you posted. Both should give galvanic protection, but the 2nd diagram seems to negate the alleged benefits of bonding the AC and DC circuits, namely the "better" operation of the RCD, in which case i don't see the point of the bonding and fitting of the GI.

 

[lpdsn]

I'm a bit puzzled by the diagrams you posted. Both should give galvanic protection, but the 2nd diagram seems to negate the alleged benefits of bonding the AC and DC circuits, namely the "better" operation of the RCD, in which case i don't see the point of the bonding and fitting of the GI.

Say there is a short between live and earth inboard of the consumer unit (RCD). The earth wire being equal to the live wire the earth will be at approx half the live voltage if it were just relying on the earth wire all the way back to where the shorepower is earthed. The GI will conduct and the DC ground (to the sea through the keel, prop shaft etc.) however will pull the earth voltage much lower. It won't affect the operation of the RCD in the consumer unit as that will just be triggered by the imbalance between the currents in the live and neutral wires, regardless of the path to earth of the short. The RCD won't behave differently in either diagram.

 

[Normalfornorfolk]

Barnacles causing bronze prop electrolysis

Blimey! Pages of erudite discussion on how barnacles might control electrolysis!

Just one thing puzzles me. What connection is there between barnacles and electricity? Is there one? I very much doubt it.

Penny to a pinch of electrons if barnacles are eroding your prop it's simple bio-chemical (ie the plainly obvious reason) and not electrolytic action, just as they don't erode their rocky hidey-holes electrolytically. After all, how could they have learned this trick when electrickery has only been around in boats for a century or so - a nanosecond in evolutionary time.

Electrolytic barnacles! Sounds like a line in an insurance scam or a 1950s space horror movie, it's that unfeasible.

 

[RichardS]

Blimey! Pages of erudite discussion on how barnacles might control electrolysis!

Just one thing puzzles me. What connection is there between barnacles and electricity? Is there one? I very much doubt it.

Penny to a pinch of electrons if barnacles are eroding your prop it's simple bio-chemical (ie the plainly obvious reason) and not electrolytic action, just as they don't erode their rocky hidey-holes electrolytically. After all, how could they have learned this trick when electrickery has only been around in boats for a century or so - a nanosecond in evolutionary time.

Electrolytic barnacles! Sounds like a line in an insurance scam or a 1950s space horror movie, it's that unfeasible.

I don't remember Vic saying anything of the sort .... where did you get that quote from?

But forget all that .... it's the risk of explosion which should remain uppermost in our minds.

Richard

 

[Hydrozoan]

Yes, it is unfair to VicS to take a catchy thread title, omit its question mark and misattribute to him the opinion that barnacles ‘control’ electrolysis in a way you lampoon as akin to an insurance scam or horror movie. AFAICS he and others were discussing GI in relation to another question raised in the thread.

Of course it could well be simply chemical action as you emphasize, but it would also not be unreasonable to think that an organism might affect an electrochemical process at the interface where it lives – e.g.: ‘The biological film contributes to an alteration of surface energy and the electrochemical behaviour of metals is modified in the presence of metabolic products ...’ (https://www.copper.org/applications...es/biofouling/basics_and_experience.html#eff3). Whether or not an interaction of that kind might be operating in the OP’s case I do not know, but I would not dismiss the possibility out of hand.

Moving on, you prompted me to find out how much ‘erosion of their rocky hidey-holes’ sessile barnacles actually do. Some species, globally, are rock borers but AFAICS common UK species do not actively erode rock (though a biologist may correct me on that).

However, one Northern Hemisphere species has recently been found to be in a symbiotic relationship with cyanobacteria, which excrete organic acids that dissolve carbonate rock (https://www.newscientist.com/articl...-down-to-microbe-builders-and-barnacle-chefs/.) It would not surprise me if other species are found to have similar relationships, and by them produce acids or natural complexing agents that may dissolve copper and/or affect its electrochemical corrosion.

 

[Flica]

Yes, it is unfair to VicS to take a catchy thread title, omit its question mark and misattribute to him the opinion that barnacles ‘control’ electrolysis in a way you lampoon as akin to an insurance scam or horror movie. AFAICS he and others were discussing GI in relation to another question raised in the thread.

Of course it could well be simply chemical action as you emphasize, but it would also not be unreasonable to think that an organism might affect an electrochemical process at the interface where it lives – e.g.: ‘The biological film contributes to an alteration of surface energy and the electrochemical behaviour of metals is modified in the presence of metabolic products ...’ (https://www.copper.org/applications...es/biofouling/basics_and_experience.html#eff3). Whether or not an interaction of that kind might be operating in the OP’s case I do not know, but I would not dismiss the possibility out of hand.

Moving on, you prompted me to find out how much ‘erosion of their rocky hidey-holes’ sessile barnacles actually do. Some species, globally, are rock borers but AFAICS common UK species do not actively erode rock (though a biologist may correct me on that).

However, one Northern Hemisphere species has recently been found to be in a symbiotic relationship with cyanobacteria, which excrete organic acids that dissolve carbonate rock (https://www.newscientist.com/articl...-down-to-microbe-builders-and-barnacle-chefs/.) It would not surprise me if other species are found to have similar relationships, and by them produce acids or natural complexing agents that may dissolve copper and/or affect its electrochemical corrosion.

Looks like we're agreeing that a) barnacles do make holes in bronze and b) it's a chemical NOT an electrogalvanic process.

Never mind the trolls who wander this as any other website, even if they are from Norfolk. Pity "Norman" can't be as helpul an informant as VicS - who's consistenly good for a bit of knowledge-based commonsense.