Jump to content

Galvanic Erosion


Featured Posts

2 hours ago, Raz said:

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.

Its a sad story with a sad ending I think all insurance companies try to spin things out to end the way that they want it! I had a claim against BW years ago, it only ended with them paying up because one of my customers was a QC. I did him a favour and he did me the same and BW backed down 

Link to comment
Share on other sites

Just to add my own experiences into this, as many people here already know we suffered a severe corrosion problem last year. The boat had suffered no corrosion in its first 23 years of life, had always been connected to a shoreline using a GI, and had been on the same mooring for 10 years. Then suddenly during the next 2 years the whole hull pitted to the point of almost complete penetration and needed a complete overplating. We are still not certain what caused it. The only thing that changed was the fitting of a new engine, maybe that caused it; there seems to be possibility that the vastly increased power of its alternator may have driven enough stray currents through the hull to cause the problem.

The piling at our mooring is plastic. Four boats share the same supply; the other 3 were unaffected; two of those did not have GIs. Later this summer I will have the boat docked and rechecked, it is disconcerting not to know why the problem occurred or whether it has now been fixed.

Link to comment
Share on other sites

16 minutes ago, Keeping Up said:

it is disconcerting not to know why the problem occurred or whether it has now been fixed.

Agreed. Yours is certainly a puzzler. We went through everything we could think of. 

Oh, one thing that I don't believe was discussed... was the steel-eating microbe dismissed?

Link to comment
Share on other sites

1 hour ago, Keeping Up said:

Four boats share the same supply; the other 3 were unaffected; two of those did not have GIs.

Sadly, a problem with another boat can often be the issue and it's someone else's hull or fittings that pay the price.

Link to comment
Share on other sites

24 minutes ago, jddevel said:

 Just read quite an intriguing article on Wikipedia about this subject. Anyone know where I can get a gold plated hull cheap?

Blacked is probably better than gold plated - it's cheap to touch up. 

Link to comment
Share on other sites

And, if the gold plating gets scratched, it won't protect the hull, which will corrode more rapidly. Gold has a potential of +1.5V, as against iron at -0.44V , with reference to a hydrogen electrode. That's nearly 2V galvanic potential.

 

edited to add: in the Wikipedia article, compare the galvanised corrugated iron and the tin can

Edited by Iain_S
Link to comment
Share on other sites

Just now, Iain_S said:

And, if the gold plating gets scratched, it won't protect the hull, which will corrode more rapidly. Gold has a potential of +1.5V, as against iron at -0.44V , with reference to a hydrogen electrode. That's nearly 2V galvanic potential.

So the logical conclusion is to plate the hull with... more steel!

Link to comment
Share on other sites

57 foot narrow boat estimated around 65 sq metres indicates a estimated cost over £800 Using Zingas` online calculater although they indicate allowing for a 20 percent wastage which seems a lot. Is that about right Peterboat what was your spec?

Link to comment
Share on other sites

  • 2 weeks later...

I'm a bit late to this thread but maybe I can throw in some more info to be considered. I've no direct experience of steel built narrowboats corroding away but do have 10 years+ experience of galvanic isolators on plastic boats! That gives me some evidence to try and 'guess' what is going on. I'm a scientist – a chemist by training – but my PhD was in 'hindsight and the bleeding obvious'. Apologies in advance for the long post.

We bought our first expensive boat in 2002, a 40ft GRP sailing yacht (bought new). It was a cruiser/racer which we raced round the cans up in Scotland plus a few races across the North Sea to Norway. These boats use Saildrives – an aluminium casting that comes out the bottom of the boat that holds the prop. Most racers use expensive folding props which have their own anodes built in plus anodes on the sail drive itself. Ours was moored in the marina when not out and about and connected to shore power. Ours was out of the water for antifouling every 12 months and every 3 months in the racing season we dived on it to clean the bottom so could check the anodes. The first set on the prop lasted 9 months and were replaced at the next lift out. Same again, 9 months later they were shot. The saildrive anodes were fine. The prop was also looking a bit worse for wear – possibly the de-zincification of the bronze prop.

At the time, a number but not all of the boats around us were suffering the same rapid ware on their prop anodes but there were parts of the marina where all the other racers did not suffer. We therefore put a Galvanic isolator on and for the next 4 years the problem went away. Another boat did the same and he cured his problem. Others without GI's had the same issues as before. I was convinced that our GI had made a big difference in the area we were in in the marina and suspected there was something wrong with our end of the marina although despite many tests by a lot of people, nothing was found or done.

In 2008, we gave up racing and sailed the boat down to the Algarve and onto Greece over 2 years. On our way we heard lots of similar stories and perhaps found that only 1 in 5 boats were using GI's. We did come across though one 'dramatic' case – perhaps similar to the one in this thread – where the owners (who became close friends) told us of their corrosion problems on their 'new' German Built 40ft yacht where they were on their 3rd saildrive – the 2 previous ones having disintegrated through corrosion despite anodes in less than 12 months each. They didnt have a GI but like us, before they went off cruising had moored their boat in a marina on shore power. This particular make of boat uses an interesting design for shore power. The 240v circuit always used the 3KV inverter that was installed – ie when on shore power, the supply was only to the battery charger which then charged the batteries – which then in turn supplied the inverter and power to the 240V sockets. The boat manufactures had fitted the 3rd saildrive and done a lot of other 'stuff' and the problem seemed to have gone away – after a year cruising, the saildrive was still fine. No one in their home marina had had any significant issues.

All of the above leads me to believe you can split these electrolysis problem into 3 digestible chunks

  1. you are moored in an area where earth circuits do not occur easily and/or your boat is not susceptible to being part of a galvanic cell and you do not see noticeable issues.

  2. You do end up in an area /or your boat is more susceptible to problems where there is a possibility of being part of a galvanic cell and if no precautions are taken then part of your boat will start to disappear -but seems treatable by use of a galvanic isolator. This seems to fit the case I described above with our position in the marina having caused the problem in surrounding boats – but not all. I firmly believe the severity of the problem will be a function of both the boat and the surroundings but is easily solved.

  3. The final one is the catastrophic failure as noted in this thread and our friends German boat. Here something went very wrong with both and is difficult just to put down to the 'typical' galvanic issues. My guess would be on the German GRP boat, there was some sort of issue with the electrical set up on the boat far worse than most other GRP boats. Similarly for this thread boat, something went badly wrong and no one has isolated the real cause.

What I am not hearing both now on this forum or from my experiences that there are not a lot of instances between 2) and 3). As a scientist I would expect a 'normal distribution' of galvanic problems but they seem to be either fairly minor (as per my problem) or catastrophic (as in this case). That says to me that they are caused by two different 'Root' causes – although highly likely they are both electrically initiated. Perhaps a GI is all that is needed to resolve (2). Our plastic boat was very happy living on shore power with a GI for 4 years but very unhappy for 2 years without one. I guess the effect is more difficult to tell on a steel NB.

  • Greenie 1
Link to comment
Share on other sites

4 hours ago, Dr Bob said:

I'm a bit late to this thread but...

Better late than never Dr Bob! Good to hear about your experiences, which follow along similar lines to what I learned in the yachting environment, though not through personal experience but rather through that of others.  I learned there that certainty was a rather elusive beast, but it does seem that there's yet more uncertainty on the cut!  Your observations and your professional perspective are very welcome additions to the information pool.

In my view, a GI is an essential precaution for anyone contemplating a shore connection, but the more I live with mine (which at least does have a visible meter indication) and read about the experiences of others, the more I wonder if it's enough. I'm beginning to hear an Isolation Transformer calling!

Link to comment
Share on other sites

13 minutes ago, Sea Dog said:

Better late than never Dr Bob! Good to hear about your experiences, which follow along similar lines to what I learned in the yachting environment, though not through personal experience but rather through that of others.  I learned there that certainty was a rather elusive beast, but it does seem that there's yet more uncertainty on the cut!  Your observations and your professional perspective are very welcome additions to the information pool.

In my view, a GI is an essential precaution for anyone contemplating a shore connection, but the more I live with mine (which at least does have a visible meter indication) and read about the experiences of others, the more I wonder if it's enough. I'm beginning to hear an Isolation Transformer calling!

We're just about to buy a NB without either so its either £80-150 or £340. The yacht experience tells me that a GI should be ok for the intermediate case. I am not sure anything other than fixing what ever is causing the 'catastrophic' problem will solve the worst case and may be independent of a shore to boat earth path. Good discussion though!

Link to comment
Share on other sites

1 hour ago, Dr Bob said:

We're just about to buy a NB without either so its either £80-150 or £340. The yacht experience tells me that a GI should be ok for the intermediate case. I am not sure anything other than fixing what ever is causing the 'catastrophic' problem will solve the worst case and may be independent of a shore to boat earth path. Good discussion though!

As  I understand it, a GI will indeed do the job under most circumstances, but an IT physically completely isolates your boat from the shore earth so ought to always protect against stray current corrosion.

The difficulty in fixing what's causing the 'catastrophic' problem itself is that it's quite likely to be something unknown to the owner of the boat which actually has the stray current fault... and the pitting it's causing is in someone else's bloomin' steelwork!

Good luck with the new boat - I hope she's all you hope she'll be. :)

Link to comment
Share on other sites

10 hours ago, ditchcrawler said:

Saw these this week,  what does the team think

DSCF4806small.jpg

DSCF7333small.jpg

If the first one is used to connect the hull to the piling and thus the soil and water I think that it will be setting up a cell so corrosion is inevitable. At least the piling is galvanised so with a bit of luck that will be eaten first but then what?

No idea about the second photo without knowing what's on the other end of the cable. maybe its a centre anode which is probably OK or maybe its another ground connection completing a cell circuit and that is not. Anyway I can not see much signs of heat damage to the paint at the boat end so maybe its just glued on, in which case its insulated and a waste of time, effort and money - whatever the owner thinks it is supposed to do.

  • Greenie 2
Link to comment
Share on other sites

Create an account or sign in to comment

You need to be a member in order to leave a comment

Create an account

Sign up for a new account in our community. It's easy!

Register a new account

Sign in

Already have an account? Sign in here.

Sign In Now
  • Recently Browsing   0 members

    • No registered users viewing this page.
×
×
  • Create New...

Important Information

We have placed cookies on your device to help make this website better. You can adjust your cookie settings, otherwise we'll assume you're okay to continue.