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BD3Bill

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So, why when permanently moored and connected shorepower do we allow our boats and anodes to erode? Surely if I connect an earth wire from the common at the engine bed to a length of earth wire connected to a ground spike a couple of feet in the bank this is an easier path for stray current to take back to the sub station??? Or not.          BE NICE  !   

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31 minutes ago, BD3Bill said:

So, why when permanently moored and connected shorepower do we allow our boats and anodes to erode? Surely if I connect an earth wire from the common at the engine bed to a length of earth wire connected to a ground spike a couple of feet in the bank this is an easier path for stray current to take back to the sub station??? Or not.          BE NICE  !   

 

What about the boat next to you that then uses your hull and 'spike' to get to earth ?

 

 

Galvanic Corrosion.gif

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29 minutes ago, BD3Bill said:

So, why when permanently moored and connected shorepower do we allow our boats and anodes to erode? Surely if I connect an earth wire from the common at the engine bed to a length of earth wire connected to a ground spike a couple of feet in the bank this is an easier path for stray current to take back to the sub station??? Or not.          BE NICE  !   

It'll do something,don't know exactly what,but in a different incarnation,we always used a groundspike when re-fuelling aircraft with a wire crocodile clipped to the fuel tank and the other end on the groundspike.

Rumour had it that it led any static to earth.

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It's not about earthing.

Two boats floating around create a cell with the water as the electrolyte. When both boats are earthed, the result is that both boats are connected and the circuit for this cell is complete. It's a poor cell and the current flowing is tiny but the cumulative effect can be serious erosion.

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36 minutes ago, Alan de Enfield said:

 

What about the boat next to you that then uses your hull and 'spike' to get to earth ?

 

 

Galvanic Corrosion.gif

But I don’t have a boat next to me, I am on an arm, linear fashion. I see you point, but not in this case. So? The stray current from the boat astern travels to my hull, thence by cable to earth, without waisting my anodes and hull? Further more your example shows the problem that occurs for dissimilar metals, not my situation....... thanks though for your comment Alan. 

 

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50 minutes ago, Mad Harold said:

It'll do something,don't know exactly what,but in a different incarnation,we always used a groundspike when re-fuelling aircraft with a wire crocodile clipped to the fuel tank and the other end on the groundspike.

Rumour had it that it led any static to earth.

Thanks Harold but my boat doesn’t move fast enough to create static......

16 minutes ago, Sir Nibble said:

It's not about earthing.

Two boats floating around create a cell with the water as the electrolyte. When both boats are earthed, the result is that both boats are connected and the circuit for this cell is complete. It's a poor cell and the current flowing is tiny but the cumulative effect can be serious erosion.

But if I provide a path of less resistance with a wire instead of the water then the current flows that way instead! No? 

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An interesting experiment!  I guess we’ll not know the answer for sure for a few years, when you will either have a set of sparkly anodes, or will have waisted effort banging in an earth pin every time you hook up.  Personally, I go for the overkill with anodes, but even with 10 costing 60 quid each and lasting at worse four years, 3 quid a week is a worthwhile sacrifice! 

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My anodes are still reasonable after 6 years....... of being 12v only. Now I am hooked up I do want to avoid any bad stuff, and no I don’t want to fit a galvanic isolator or a isolating transformer. I’m not moving anywhere! If I go for a cruise it’s a moot point! 

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I think if all the local boats had a great big thick wire connected to a huge ground spike, and ideally the same ground spike, then all would be well.

 

I suspect the problem starts when due to various leakage currents etc the earth wire is not exactly at earth potential and so there is a small voltage between boats that have a really good earth and those that don't. This is what does the damage. You cannot assume that the mains earth is really at earth potential, and you can't assume that an earth spike is a good earth, especially in a dry summer. 

 

............Dave

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When I helped a mate black his boat this year, his anodes had a steel deposit about half an inch thick on top of them.  Sadly I don't have a photo of it, but I was gobsmacked.

 

We can only think that he wasn't the donor boat, as his hull was in good nick!

 

1 hour ago, BD3Bill said:

Now I am hooked up I do want to avoid any bad stuff, and no I don’t want to fit a galvanic isolator or a isolating transformer.

 

I hope you like buying boats then!  

 

If you are linked into a common earth electrical circuit with other boats, you are part of the circuit.  It all depends on how your boat was wired and how their boats were wired, and you have no control over theirs.  

 

If you are lucky, you gain steel.  If you are not lucky, you lose steel.  Long enough hooked up and you might sink!

 

I don't worry about it, as I have spent less than a week on hookup in the last 5 years, and my hull is in great condition for a 40 year old boat.  If I was on shore power, I would fit an isolating transformer before connecting the cable, as they are better than galvanic isolators, but I would settle for a GI if funds were tighter.

 

If you think that's woo-woo, feel free, but I think it's physical chemistry ... and I have seen 4 year old boats that looked like colanders or sieves!

 

 

 

 

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If your on a shoreline fit a GI or IT.

 

of course if you know better than don’t bother it’s no skin off my nose or more accurately no metal off my boat...

 

ypu might be lucky and the combination of earth potentials, metals, contaminants in the water and your boat wiring might mean your ok....

 

 

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12 hours ago, BD3Bill said:

So, why when permanently moored and connected shorepower do we allow our boats and anodes to erode? Surely if I connect an earth wire from the common at the engine bed to a length of earth wire connected to a ground spike a couple of feet in the bank this is an easier path for stray current to take back to the sub station??? Or not.          BE NICE  !   

 

Your basic premise is incorrect. If you isolate the common earth while on shore power using a good quality galvanic isolator or isolation transformer then you've taken the right steps to prevent galvanic corrosion. If you connect your boat to earth as you suggest you will just be connecting to other boats and metal pilings in the vicinity and will encourage galvanic corrosion.

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10 hours ago, BD3Bill said:

My anodes are still reasonable after 6 years....... of being 12v only. Now I am hooked up I do want to avoid any bad stuff, and no I don’t want to fit a galvanic isolator or a isolating transformer. I’m not moving anywhere! If I go for a cruise it’s a moot point! 

 

I'm sorry, you say you want nice responses on this thread but you really need to ditch what you think you know about the subject because it's all wrong. No question is silly but not listening to the answers is very silly indeed. Listen to what  people are telling you and do some reading around the subject.

Edited by blackrose
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9 hours ago, dmr said:

I think if all the local boats had a great big thick wire connected to a huge ground spike, and ideally the same ground spike, then all would be well.

 

No, because you'd then have dissimilar metals immersed in an electrolyte all connected together which is the basis for galvanic corrosion to occur. Different steel will have slightly different nobilities and some will become anodic and some cathodic.

 

I'm amazed that you don't realise this Dave?

 

* If anyone wants to connect their boat to earth then assuming your boat is hull-earth bonded (many aren't and have fitted GIs without realising), then the simplest way is to remove your GI or IT and plug into shore power. I'm not sure why you'd want to do that but carry on by all means! 

 

 

Edited by blackrose
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9 hours ago, TheBiscuits said:

When I helped a mate black his boat this year, his anodes had a steel deposit about half an inch thick on top of them.  Sadly I don't have a photo of it, but I was gobsmacked.

 

We can only think that he wasn't the donor boat, as his hull was in good nick!

Isn't he therefore the boat with the issue as he's stealing metal from neighbouring vessels?

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12 hours ago, BD3Bill said:

But I don’t have a boat next to me, I am on an arm, linear fashion. I see you point, but not in this case. So? The stray current from the boat astern travels to my hull, thence by cable to earth, without waisting my anodes and hull? Further more your example shows the problem that occurs for dissimilar metals, not my situation....... thanks though for your comment Alan. 

On a linear mooring - so - I guess you have a boat in front of you rather than alongside.

Both (all) boats connected to the mains.

I suppose you have a steel hull, stainless steel shaft, and a bronze prop.

 

So, as you say, nothing like the illustration I posted.

 

If you look at the Galvanic table, you will see that the 1st thing that the escaped electrical worms will do is attack the manganese even before they get to the steel of the hull, they then have to travel thru the hull to get to your 'earth strap'.

 

 

Galvanic Order of Metals A - C 2.jpg

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2 hours ago, blackrose said:

 

No, because you'd then have dissimilar metals immersed in an electrolyte all connected together which is the basis for galvanic corrosion to occur. Different steel will have slightly different nobilities and some will become anodic and some cathodic.

 

I'm amazed that you don't realise this Dave?

 

* If anyone wants to connect their boat to earth then assuming your boat is hull-earth bonded (many aren't and have fitted GIs without realising), then the simplest way is to remove your GI or IT and plug into shore power. I'm not sure why you'd want to do that but carry on by all means! 

 

 

 

Are you sure? I have never heard of this before. I thought it was generally accepted that even dissimilar metals were actually ok as long as they were very close on the potential scale, and any variation in steel potential from boat to boat is going to be very small. I believe it is potentials created by volt drops along the earth lines that is the real danger.

 

If you are correct then surely a boat would dissolve itself its its overplated or repaired with steel from a different batch?????

 

................Dave

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8 hours ago, blackrose said:

 

Your basic premise is incorrect. If you isolate the common earth while on shore power using a good quality galvanic isolator or isolation transformer then you've taken the right steps to prevent galvanic corrosion. If you connect your boat to earth as you suggest you will just be connecting to other boats and metal pilings in the vicinity and will encourage galvanic corrosion.

Smashing, the very answer I was looking for, thank you.

 

 

17 hours ago, TheBiscuits said:

When I helped a mate black his boat this year, his anodes had a steel deposit about half an inch thick on top of them.  Sadly I don't have a photo of it, but I was gobsmacked.

 

We can only think that he wasn't the donor boat, as his hull was in good nick!

 

 

I hope you like buying boats then!  

 

If you are linked into a common earth electrical circuit with other boats, you are part of the circuit.  It all depends on how your boat was wired and how their boats were wired, and you have no control over theirs.  

 

If you are lucky, you gain steel.  If you are not lucky, you lose steel.  Long enough hooked up and you might sink!

 

I don't worry about it, as I have spent less than a week on hookup in the last 5 years, and my hull is in great condition for a 40 year old boat.  If I was on shore power, I would fit an isolating transformer before connecting the cable, as they are better than galvanic isolators, but I would settle for a GI if funds were tighter.

 

If you think that's woo-woo, feel free, but I think it's physical chemistry ... and I have seen 4 year old boats that looked like colanders or sieves!

 

 

 

 

I don’t take your advice as woo-woo at all, and thank you. I will take the advice given and spend the money now. Cheers 

 

 

 

 

 

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7 hours ago, Alan de Enfield said:

On a linear mooring - so - I guess you have a boat in front of you rather than alongside.

Both (all) boats connected to the mains.

I suppose you have a steel hull, stainless steel shaft, and a bronze prop.

 

So, as you say, nothing like the illustration I posted.

 

If you look at the Galvanic table, you will see that the 1st thing that the escaped electrical worms will do is attack the manganese even before they get to the steel of the hull, they then have to travel thru the hull to get to your 'earth strap'.

 

 

Galvanic Order of Metals A - C 2.jpg

Thank Alan, yes that’s right, and those boats aren’t in great shape, one is riveted iron and the other is very rusty along the water line indeed. I was just thinking out loud. Good advice on the forum as always. Cheers 

 

 

 

 

17 hours ago, jonathanA said:

If your on a shoreline fit a GI or IT.

 

of course if you know better than don’t bother it’s no skin off my nose or more accurately no metal off my boat...

 

ypu might be lucky and the combination of earth potentials, metals, contaminants in the water and your boat wiring might mean your ok....

 

 

Got it, advice will be taken, thank you very much. 

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