Galvanic Erosion

[Mikexx]

3 hours ago, jddevel said:

Am I right in assuming that galvanic corrosion only really takes place when the boat is moored and not really important when in motion? This may be a stupid question and you may wonder why I ask but I may have a "cunning plan" as one of my heroes would say> 

A shoreline without the require protection can cause galvanic corrosion, which obviously won't happen on the move.

Localised galvanic corrosion can still occur with no shore line; from the prop being a more noble metal and impurities in the steel but the whole point of anodes is to stop the galvanic form of corrosion.

However steel rusts naturally in the presence of water and oxygen, albeit at a slower rate.

Edited April 17, 2017 by Mikexx

[WotEver]

30 minutes ago, Mikexx said:

A shoreline without the require protection can cause galvanic corrosion... 

Point of order. A shoreline can cause Stray Current Corrosion. 

[Mikexx]

3 minutes ago, WotEver said:

Point of order. A shoreline can cause Stray Current Corrosion. 

Given the supply is AC, any DC current will be from either a local groundspike or copper buried in the ground at the local substation. So the current will be galvanic in its source.

By definition 'stray' implies unknown source or destination. I think shoreline currents are well known. I think it is best to use the term "shoreline current" where we use shoreline isolators, or perhaps galvanic isolators, to negate the effect. :-)

[Captain Pegg]

On 4/16/2017 at 10:28, Mikexx said:

 

This article:

 http://www.corrosionclinic.com/types_of_corrosion/pitting_corrosion.htm

suggests that inclusions of Manganese is a major culprit of pitting. I would expect the inclusion of a more noble material would cause pitting.

  https://en.wikipedia.org/wiki/Pitting_corrosion

highlights the anodic effect of an area that has lost its surface rust. I presume any layer of rust is more cathodic in nature than the steel below.

 

All steel has manganese in its composition. It is added specifically to create Manganese Suphide (MnS) which is the substance that the article is about. Manganese is added because it reacts with naturally occurring sulphur more readily than iron and has a far higher melting point than Iron Suphide and therefore is an aid to the manufacturing process.

High manganese steels are commonplace in my line of work and no provision is made for corrosion due to the specific composition. It may be part of the science of corrosion but that doesn't mean it is significant in everyday use.

As the piece you link to states, the primary reason for corrosion of steel is the environment. Naturally it's actually pretty good at corrosion resistance until something attacks the surface layer of oxide. Chlorides are the usual culprit.

JP

[mark99]

2 hours ago, Mikexx said:

Given the supply is AC, any DC current will be from either a local groundspike or copper buried in the ground at the local substation. So the current will be galvanic in its source.

By definition 'stray' implies unknown source or destination. I think shoreline currents are well known. I think it is best to use the term "shoreline current" where we use shoreline isolators, or perhaps galvanic isolators, to negate the effect. :-)

 

Or badly installed solar array like mentioned present at the mooring. (Solar present that is).

Edited April 17, 2017 by mark99

[sjc]

Sorry to hear this, a very sad story, it is your worst nightmare as a boat owner.

Is it possible the corrosion was already underway when you bought the boat but you were not warned about it ?

Failing that something must have changed since you took ownership ?  Any new equipment on the boat, any new electrical work done, and changes in neighbouring boats / equipment, did the previous owners keep it constantly connected to the shoreline, have you kept the same mooring, and shoreline supply.  Although the GI was working, did it have an LED indicating when it was conducting, and if so did you ever check it randomly to see if it was on.

If it spent more time on shoreline than cruising, it is a fair assumption to assume this is where the corrosion took place.  The only other possibility is perhaps a faulty supply, with a DC voltage on your earth perhaps ( possibly as indicated on the solar farm document referenced in an earlier post ). ( hence the GI LED question ).  I believe marina's must comply with strict safety standards for electrical supply, maybe EOG moorings are unregulated ?

Having read this and the other recent thread on corrosion our boat is out of the ware, ha all electrics removed, and is completely encased in fibre glass...

 

 

[I Spartacus]

I have read all of this thread . Could an electric fence have  cause this problem as the OP said it was an end of field mooring on a farm ?

Edited April 18, 2017 by I Spartacus

[Raz]

6 hours ago, I Spartacus said:

I have read all of this thread . Could an electric fence have  cause this problem as the OP said it was an end of field mooring on a farm ?

Just to provide an answer for the last two posts. Yes, ours was an end of garden mooring on a farm on the offside of the canal.

There was no electric fence anywhere near, but around 100 metres away the landowner had an array of solar panels on the roof of a steel barn that provided backup to his own mains supply. He provided shore power to ours and a couple more boats on the moorings.

We bought the boat when she was in the first months of her fifth year in March 2009. There were no signs of hull corrosion at that time, and she had been last blacked by the previous owner 6 months previously, done himself at the Ellesmere dry dock. I paid to have her blacked again at the end of our first season, 6 months after we bought her. I paid a local marina to do the work, specifically asking them to inspect the the condition of the hull and anodes. They reported back that there were no issues, although I didn't see the boat out of the water on that occasion, placing my trust in the marina.

The previous owner did not leave the boat connected to shore power - he didn't even have a battery charging system installed other than the two alternators. He occasionally used a car battery charger while there.

When we took the boat over I installed a C-Tech marine multi stage smart charger to charge two 100ah leasure batteries and one engine battery. We were away from the boat during weekdays, returning on a Friday evening until Sunday evening. We left her connected to shore power permanently with the battery charger on.

Our Galvanic Isolator was a model that did not have the led to show it was activated, but I checked it annually to test if it was in working order using an electronic multi-meter as per its instructions.

After our first blacking 6 months after we acquired her / 12 months after the last owner's, I returned it to the same marina in Spring 2012, with the same inspection instructions, she was again returned to me with "no reported issues".

During the Summer of 2013 I noticed fizzy rust bubbles on the waterline and reported this to the marina. I suggested using perhaps a branded rust killer at the next blacking. After the marina manager had consulted their "technical team" they suggested a grit blast back to bare metal followed by two pack blacking on the next occasion, which was February 2014. I gave the same inspection instructions, and we agreed a job to take a week to allow proper paint curing etc. I also requested that the packing be replaced on the prop shaft gland as a matter of routine while she was out of the water, as I had no idea if it had ever been done. It was not leaking any more than normal during use.

The marina manager rang me just 3 days after work was scheduled to start to tell me it was complete, back in the water and ready to collect. This was 4pm on a Friday afternoon. I arranged to collect on Saturday morning, thinking at the time this was too soon.

When we arrived on Saturday morning we found her on the bottom. I reported it to the marina manager, keeping fairly calm as I believed the marina owner or his insurer would put things right. I was wrong on that one. During discussions it also transpired the shaft gland packing job I asked for hadn't been done either, but this had nothing to do with the sinking. I supervised the start of the pumping operation, and at the end of the day left, telling the manager I would return during the week with my surveyor, and I expected the boat to be ashore by then.

On returning with my surveyor and seeing her ashore, we could both see the very poor blacking job, as well as the severely peppered hull with very deep pitting on the starboard side. My surveyor also suggested the anodes, although in reasonable condition, should also have been replaced, but were not.

I informed my own insurer as you are required to do in such circumstances, and also asked the marina owner, via his manager to provide details of their insurer. I received no reply. (Solicitors received the same no reply on two further occasions).

Apologies for the long post, but as this is about preventative maintenance, I wanted to relate how this could happen even if you try your best with regular maintenance which failed miserably in my case. I firmly believe that had I not left her connected to shore power, where there was obviously some kind of fault, either in our boat, the supply, or another nearby boat, this probably wouldn't have happened. It is just unfortunate that after the event it also appears to me things were compounded perhaps by the marina ignoring what was happening until it was too late.

[WotEver]

I suspect, as I said right at the beginning, that your GI was swamped with a pretty high DC voltage on the earth feed. This, coupled with a piss-poor job from the marina resulted in a sunken boat. 

Lessons to be learned? If you use a GI then be sure to fit one with LED indication and look at it very regularly. Better yet, use an IT. Secondly, when the hull is jet-washed prior to blacking inspect it yourself. If you see ANY shiny pits then be very wary. 

Tony 

Or don't use a shore line. But that's pretty silly. 

[Mikexx]

7 hours ago, I Spartacus said:

I have read all of this thread . Could an electric fence have  cause this problem as the OP said it was an end of field mooring on a farm ?

 

I don't believe anything low power like an electric fence could ever change the local earth potential to compromise a galvanic isolator. Electric fences are all about modest voltage and very low current.

[Mikexx]

9 minutes ago, WotEver said:

I suspect, as I said right at the beginning, that your GI was swamped with a pretty high DC voltage on the earth feed. This, coupled with a piss-poor job from the marina resulted in a sunken boat. 

Lessons to be learned? If you use a GI then be sure to fit one with LED indication and look at it very regularly. Better yet, use an IT. Secondly, when the hull is jet-washed prior to blacking inspect it yourself. If you see ANY shiny pits then be very wary. 

Tony 

Or don't use a shore line. But that's pretty silly. 

 

An AC current will render a GI useless as well.

I have to agree that you must inspect the boat for yourself, or get an surveyor's report if there is any doubt. And to check the work has been done properly.

I also lean towards using an Isolating Transformer so that a shore line is truly isolated from the hull.

This is salutary lesson for all, such a shame it is at Raz's expense.

[WotEver]

10 minutes ago, Mikexx said:

Electric fences are all about modest voltage and very low current.

Ummm... low current for sure, but I wouldn't call 2000-10,000V 'modest'. 

[system 4-50]

"There was no electric fence anywhere near, but around 100 metres away the landowner had an array of solar panels on the roof of a steel barn that provided backup to his own mains supply. He provided shore power to ours and a couple more boats on the mooring".  

Could faults in this supply be the cause of the problem?  

[WotEver]

Just now, system 4-50 said:

"There was no electric fence anywhere near, but around 100 metres away the landowner had an array of solar panels on the roof of a steel barn that provided backup to his own mains supply. He provided shore power to ours and a couple more boats on the mooring".  

Could faults in this supply be the cause of the problem?  

Sure, anything could be the cause. The facts appear to be that he had a high-ish DC voltage on the earth wire which swamped the GI and then deposited his hull onto the pilings. 

7 minutes ago, Mikexx said:

An AC current will render a GI useless as well

Yes, but it won't cause his hull to dissolve. You need a positive potential to ground to achieve that. 

[WotEver]

Of course it could be a small DC offset sitting on a larger AC voltage...

[Mikexx]

2 hours ago, WotEver said:

Sure, anything could be the cause. The facts appear to be that he had a high-ish DC voltage on the earth wire which swamped the GI and then deposited his hull onto the pilings. 

Yes, but it won't cause his hull to dissolve. You need a positive potential to ground to achieve that. 

A copper earthing rod will provide the positive potential. Either locally or at a substation/PME. If there isn't a 'very' local earth then there may well be an AC element with respect to local boat/water.

An AC voltage will also make the GI conduct (in both directions) such there will be a net +ve potential (from the earth rod) applied to the hull.

My father was a BT engineer and I recall him recounting stories of local earths around power stations and major substations where the phone lines were 100V or so with respect to local round. That gives you an idea of the ground currents you can get and the consequence.

The fact that Raz's earth came from a 'barn installation' suggests the earth might have originated a long way from the boat and be of unknown providence. It may have been prudent, in hindsight, to export the earth using a local earth rod, (or use an IT)

[WotEver]

Oh I'm well aware of how high the earth wire can sit. At a place I worked in the 70s we regularly measured 125V between earth & neutral. 

I'm not sure that a local earth spike would have been permitted in Raz's installation; there are all kinds of rules about that with TT, PME etc which are way outside my area of expertise. 

I am convinced that an IT is always a superior approach when compared to a GI under any circumstances but in Raz's case it would appear that it was essential. 

[sjc]

Did anything on the smart charger you installed touch the hull ? ( earth connection, case, mounting screws etc ).

The fact the previous owner never left it connected to the shoreline may be answer, maybe EOG moorers should be wary of this and use an IT.

Whether it was the soar array or just a floating earth, we may never know unless your insurers look into it further.

I hope that isn't the end of your canal boating, the other issue is none of us know how our insurers will respond until it is too late - typical...

[Raz]

8 minutes ago, sjc said:

Did anything on the smart charger you installed touch the hull ? ( earth connection, case, mounting screws etc ).

The fact the previous owner never left it connected to the shoreline may be answer, maybe EOG moorers should be wary of this and use an IT.

Whether it was the soar array or just a floating earth, we may never know unless your insurers look into it further.

I hope that isn't the end of your canal boating, the other issue is none of us know how our insurers will respond until it is too late - typical...

The C-Tech charger was plastic cased and contained guarantees within its literature that there would be nebligable stray currents in use - checked after the event. It was screwed with short brass screws to oak faced ply lining of the internal cabin at waist height within the stern storage area, plugged into one of the normal internal 13A mains sockets.

With hindsight, I would recommend using an isolation transformer. I too think this might have prevented our issues.

My insurer instructed a specialist surveyor, who concluded the hull corrosion was down to "galvanic corrosion" - perhaps a generic term he used to me who might not understand a more complicated explanation. As such, after his report, my insurer declared it to be "wear and tear" and not covered by my insurance. I agreed with this, and repairs to the hull would have to be funded by me.

Unfortunately this event was the end of our boating. My insurer, Craftinsure (although they passed my claim to their underwriters Navigators and General), refused to provide new for old replacements during repairs, according to the Craftinsure schedule. This meant, against the appointed repair contractor's advice, that submerged alternators, starter motor, and everything else was tested. If working it was left, in the case of the alternators. If not then they would only be rebuilt, not replaced as in the case of the starter motor. Water stained internal woodwork would also be left due to it remaining serviceable after drying out. After much argument, they agreed to repairs as a result of sinking at a value of £5k. My surveyor and the contractor who had started engine repairs suggested a cost of around £20k was more in line to do the whole job properly. They both suggested I accept payment in cash and dispose of the boat rather than accept sub-standard repairs in their opinion.

The marina owner was asked several times for their insurer's details but never replied until I had settled with my own. I had a legal team working for me funded by legal expenses cover on my home insurance policy, but still couldn't get anywhere with the marina owner. A self funded action using marine specialist solicitors was advised to cost in the region of £25k when I enquired, possibly double if the case was lost. Too risky for me.

All this took 12 months to try and sort out afterwards, until getting nowhere I sold the boat for salvage at a loss of around £25k on what she might have sold for in good condition. Unbelievably, the marina then went on to refuse to allow my boat's removal from their site until I paid for their "blacking" job in full, along with storage charges! £2,500 in total. Finally, some months later, when Craftinsure had managed to contact the marina's insurer, who then (too late for me) accepted liability and refunded Craftinsure's outlay to me, I had my Craftinsure excess of £300 refunded.

[Traveller]

This is a sad tale. GC is a subject that keeps coming up and the more I study the knowledgeable posts the more confused I become. I rarely use shore power. Not being a live-aboard I find my solar keeps my batteries topped up and if I do need leccie I run the shore line from my generator, usually to run the hoover, electric tools or sometimes the on board battery charger. I do moor against a metal pontoon but have tyres between the boat and the pontoon. The pontoons do have shore-power sockets. From what I have read I am probably very low risk but to be on the safe side should I fit a GI or IT?

[Flyboy]

On 16/04/2017 at 18:21, jddevel said:

I note that not only on my sailaway but all craft ashore have their sacrificial anodes -specifically those on the hull-  fore and aft. However corrosion appears all over the hull so is there any merit in having more attached along the hull sides? At the pace most travel is it going to affect maneuverability.

I have a 58' nb and have 8 anodes. Front,  back and 2 on the sides. The side anodes are low profile so don't project beyond the base plate as the sides angle inwards at the bottom. Sides anodes certainly won't make any noticeable difference to the performance of the boat.

[WotEver]

49 minutes ago, Traveller said:

to be on the safe side should I fit a GI or IT?

A GI would be a good idea but I wouldn't bother with an IT because...

50 minutes ago, Traveller said:

I rarely use shore power

 

[GUMPY]

A sideways thought was the GI fitted correctly I.e. in the input earth conductor?  I have seen them fitted between mains earth and hull bond which whilst it will protect the hull is all to easy to bypass with aerials etc.

[Raz]

31 minutes ago, Loddon said:

A sideways thought was the GI fitted correctly I.e. in the input earth conductor?  I have seen them fitted between mains earth and hull bond which whilst it will protect the hull is all to easy to bypass with aerials etc.

Yes, my GI installation was checked by my own surveyor to form part of his own report and was found to be correctly installed according to its instructions. It was initially looking like a report from him needed to be suitable for court, as my Navigators and General insurance claims handler was initially looking at rejecting my claim on the grounds of preventable damage caused by lack of maintenance. I had kept all my maintenance receipts, some of which showed where and when I had submitted the boat for blacking. I believe it was only when they got wind of my surveyor's ability to prove the negligence on the marina's part, and nothing to do with me that they accepted my claim for the damage as a consequence of sinking, but then went on to argue the costs involved in repairs. In the end they offered me the choice - accept their final offer, or make an official complaint to go to the Insurance Omnudsman. After 12 months of worry, getting nowhere fast and making long written replies to my insurance company and the legal team who were attempting to claim from the marina's insurer, I had had enough and bailed out.

[WotEver]

Many years ago, before the days of all these ombudsmen, we were dealing with an intransigent insurance company over a written-off car. Eventually we said "Okay, we're getting nowhere here, we'll take it to the ABI (Association of British Insurers) and put it in the hands of our solicitors." (that latter was a bluff, we couldn't possibly have afforded it). They replied by return that they would settle in full. 

Edited April 19, 2017 by WotEver