Cautionary Tale

[nebulae]

Regarding the need for steel frame fabricators to be registered,this requirement gives traceability.i.e.the source of the steel can be traced .Presumeably,if a hull builder is still in business(and is known),the source and spec can be traced .I gather that for Lloyds certification for a seagoing vessel,whether commercial or leisure steel used has to meet their spec .I wonder how many owners of new boats know the spec. of the steel used in their new craft? A number of boats on the waterways have steelwork sourced from abroad. What sec was the steel used in their construction? One worrying issue raised by the unfortunate owner was that blacking seemed to come off round the waterline very quickly.I wonder if the steel was dry and how long left between coats.

[valrene9600]

I wonder if he had insurance and if so what they had to say.

[Alf Roberts]

judging by the fuss he's making....no

[Bee]

I think its harsh to attach any blame to the owner, in fact I think its harsh to try to blame anybody, the boatbuilder, the owner, the bloke who did the gritblasting or the boatyard, this sort of procedure is routine, whoever painted it could have been a bit more observant but if, like me you are wearing goggles over glasses whenever using nasty paint or chemicals its hard to spot much at all, the nitty gritty (sorry) of this is why a 10 year old boat with some history of painting, anodes, galvanic thingy etc has a hole in it.

Edited November 27, 2014 by Bee

[valrene9600]

His latest post answers my comment on insurance.

I don' t quite understand why the insurance co. would not repair to satisfaction of surveyor.

Perhaps someone with knowledge can explain.

[jonesthenuke]

Full story not yet out, so I would have reserved judgement until all details known. I think the main point the chap might be making is about the effects of galvanic corrosion as a guide to owners.

It is the galvanic corrosion aspect of the story that worries me. Our boat spends most of its time in marina on a shoreline (with a galvanic isolator). I have been wondering recently what checks can be made that the galvanic conditions are correct, specifically that the isolator works and the anodes are effective.

 

Whilst I realise that anodes are not the whole answer, if the boat is at an inappropriate potential with respect to the marina steelwork or to other boats then corrosion will occur and could be rapid. Such a potential could presumably arise due to a fault on another boat or due to a fault with the marinas electrical supply. In this respect the very limited range of a galvanic isolator strikes me as an issue, they start to conduct at about 1V, so the earth of the electrical supply must be at very nearly the same potential as the marina steelwork in order for the system to be operable. The supply is the responsibility of the marina and I have no control over it, but seem to be rather exposed to the consequences of faults on it.

 

I am thus planning to take some action to check the conditions, followed perhaps by some further action to mitigate the risk. My intentions are broadly as follows:-

 

Short term

1. Test galvanic isolator (or change it as its about 8 years old already).
2. Check shoreline supply to ensure its earth is at same potential as the marina steelwork (walkway supports etc)
3. Check boat wiring to confirm earth integrity and freedom of leakage from ring main etc to earth
4. Check potential between boat hull and marina steelwork (crude but easy)
5. Check potential of hull using a Galvatest reference cell or similar (but need to buy one)

 

 

Longer term I am considering:-

 

• Disconnection of shoreline (but then no battery charging or frost protection heating)
• Fitting isolation transformer instead of galvanic isolator
• Using double insulated or isolated supply solely for battery charging and frost protection (keeping boat ring main isolated and not relying on galvanic isolator

I would welcome any advice on the above.

[David Mack]

Longer term I am considering:-

• Disconnection of shoreline (but then no battery charging or frost protection heating)
• Fitting isolation transformer instead of galvanic isolator
• Using double insulated or isolated supply solely for battery charging and frost protection (keeping boa ring main isolated and not relying on galvanic isolator

The best answer is an isolation transformer, then you are not reliant on a GI not conducting.

 

I can't remember the details now, but some time ago Gibbo (late of this parish) put forward the view that modern switched mode power supplies - the ones that allow you to use your laptop on anything from 100-250V ac - will put GIs into conduction for part of the ac waveform, and so if left connected for any length of time, galvanic corrosion currents can flow. With an IT, there is no path for the currents.

 

Note also that if you disconnect your shoreline to avoid the problem you *MUST* unplug it. If you simply switch off the power but leave it plugged in, the earth wire is still connected and the galvanic current will still flow.

 

 

 

[Neil2]

You would have to make a load of assumptions before taking sides in this sad story, but to me it comes across as a tale of an owner who discovered some boating facts of life the hard way.

 

As regards insurance liability surely even comprehensive insurance does not cover you for the hull rusting through unless you can prove conclusively it was someone else's fault. You are not covered for degradation of the hull any more than you are covered if your engine starts consuming huge amounts of oil, for example.

 

 

[Traveller]

This galvanic corrosion stuff worries the hell out of me, mainly because I really don't understand it all. My solution is not to use shore power or, if I do, only for short periods. In the main I keep my batteries topped up and run 240 volt stuff by connecting to my generator. I will fit solar in the spring.

[Neil2]

This galvanic corrosion stuff worries the hell out of me, mainly because I really don't understand it all. My solution is not to use shore power or, if I do, only for short periods. In the main I keep my batteries topped up and run 240 volt stuff by connecting to my generator. I will fit solar in the spring.

That's all very well, but if other boats in your vicinity are on shore power, and their anodes are worn or not "working" the hull will be happy to use your anodes instead! Even if you don't use shore power there's still a risk, especially if you don't check your anodes regularly.

[Loafer]

I think we should stop talking about this. It's worrying too many people, including myself. I'm not listening, nnaaa naaaah na aaaa

[Traveller]

That's all very well, but if other boats in your vicinity are on shore power, and their anodes are worn or not "working" the hull will be happy to use your anodes instead! Even if you don't use shore power there's still a risk, especially if you don't check your anodes regularly.

I am not disagreeing with you Neil but this is contrary to some advice/info I receive elsewhere, which only goes to emphasise why I am so confused. As it is, my anodes are checked regularly and 3 months ago they were fine. Clearly however the issue is huge and makes one question ownership of steel boats. It certainly makes me question the advisability of using any marina that has shore power.

 

​So the question remains - how does one protect a steel boat from galvanic corrosion even if the boat in question is not plugged in?

[MoominPapa]

The blog posts reek of someone casting around for someone to blame. I have a feeling that the next instalment is where our hero discovers that if your boat sinks because you fail to maintain it, the insurance company has no liability, either to fix the hull, or fix the consequential damage (your own or other peoples.) I discovered this when a boat sank in the marina due to a rusted gas locker and the insurance wouldn't pay for the damage to the boat, or damage to the blacking on other boats from leaked diesel.

 

MP.

[jonesthenuke]

I think we should stop talking about this. It's worrying too many people, including myself. I'm not listening, nnaaa naaaah na aaaa

Exactly, I for one am worried. I would be much happier if I had a some specific checks to confirm that the situation is OK.

[Gordias]

There's some information about galvanic corrosion here:

http://en.wikipedia.org/wiki/Galvanic_corrosion

 

Reading it suggests that the average narrow boat is not well protected for all normal circumstances (including, but not limited to, shore connections).

 

This seems a bit strange, because it's frequently cited as a likely cause of any "mysteriously rapid corrosion".

 

This leads to an exceptionally unsettling situation for a potential buyer:

• A boat can be significantly damaged by an invisible force
• There's no reliable way to check whether the process is occurring
• There's no reliable way to check if it has occurred (I've read that surveyors aren't obliged to find all possible "thin spots" nor liable if they miss one)
• The consequences can be severe, since some major hull repairs can damage the internal fittings

The wikipedia article seems to imply there's a whole branch of engineering dedicated to this. I wonder if any boat manufacturer or fitter has ever asked a specialist how to really protect a narrow boat from corrosion?

Edited November 28, 2014 by Gordias

[Traveller]

There's some information about galvanic corrosion here:

http://en.wikipedia.org/wiki/Galvanic_corrosion

 

Reading it suggests that the average narrow boat is not well protected for all normal circumstances (including, but not limited to, shore connections).

 

This seems a bit strange, because it's frequently cited as a likely cause of any "mysteriously rapid corrosion".

 

I wonder if any boat manufacturer or fitter has ever asked a specialist how to really protect a narrow boat from corrosion?

 

 

Yes I also wonder. Indeed I wonder how many owners have taken foolproof steps to safeguard their boat? It seems the answer is not out there or not in layman terms anyway. I had always thought no shore power and you we're basically safe, provide there were anodes in place to protect from any stray currents from other boats. What I can never get my head round with the shore power bit is how can the boat be at risk from GC if you have a properly insulated cable running from shore to say onboard charger or socket if that charger or item connect to the socket is not in contact with the hull?

Edited November 28, 2014 by Traveller

[RLWP]

You misunderstand what anodes are for. They are to protect the hull from corrosion:

 

http://en.wikipedia.org/wiki/Cathodic_protection

 

Richard

[Traveller]

Thank you, Richard. That is what I thought but became confused by Post35

 

"That's all very well, but if other boats in your vicinity are on shore power, and their anodes are worn or not "working" the hull will be happy to use your anodes instead! Even if you don't use shore power there's still a risk, especially if you don't check your anodes regularly."

[John V]

The wikipedia article seems to imply there's a whole branch of engineering dedicated to this. I wonder if any boat manufacturer or fitter has ever asked a specialist how to really protect a narrow boat from corrosion?

 

 

Flippant but accurate......build it from GRP

 

eta....even that doesn't protect rudder, skeg, propshaft, prop etc

Edited November 28, 2014 by John V

[Tony Brooks]

Thank you, Richard. That is what I thought but became confused by Post35

 

"That's all very well, but if other boats in your vicinity are on shore power, and their anodes are worn or not "working" the hull will be happy to use your anodes instead! Even if you don't use shore power there's still a risk, especially if you don't check your anodes regularly."

 

 

That quote misses out the bit that should say "if your boat has any connection to ground". Typically this would be because it is up against a steel piling or sitting on a relatively low resistance patch of mud. If you have insulating fenders then any danger is very much decreased. However there is still what I would assess as an exceptionally small risk that your boat hull might form part of a circuit from an adjacent boat with a fault on it to ground or another boat on the other side of you with a grounded hull. Steel having a lower resistance than water - even dirty canal water. The further apart the boats the less this is likely to happen or cause damage.

 

If your hull is connected to ground in some way then such a fault would definitely cause problems.

[Gordias]

 

 

Yes I also wonder. Indeed I wonder how many owners have taken foolproof steps to safeguard their boat? It seems the answer is not out there or not in layman terms anyway. I had always thought no shore power and you we're basically safe, provide there were anodes in place to protect from any stray currents from other boats. What I can never get my head round with the shore power bit is how can the boat be at risk from GC if you have a properly insulated cable running from shore to say onboard charger or socket if that charger or item connect to the socket is not in contact with the hull?

 

One issue with shore power is that there is no "perfect earth". Here's the text from wikipedia:

 

Metal boats connected to a shore line electrical power feed will normally have to have the hull connected to earth for safety reasons. However the end of that earth connection is likely to be a copper rod buried within the marina, resulting in a steel-copper "battery" of about 0.5V. For such cases, the use of a galvanic isolator is essential, typically two semiconductor diodes in series. This prevents any current flow while the applied voltage is less than 1.4V (i.e. 0.7V per diode), but allows a full flow of current in case of an electrical fault. There will still be a very minor leakage of current through the diodes, which may result in slightly faster corrosion than normal.

 

Note that it suggests a standard solution which is not, AFAIK, part of the normal narrow boat setup.

 

I'm a software guy, not an EE. but the text above suggests to me that:

• The shore line can be tested, probably with relatively cheap equipment
• Better protection is available
• The situation after installing the best possible protection can be tested

[RLWP]

Non of this protects against microbial corrosion

 

First time we saw Tawny out of the water was at her survey docking. She had deep pits with a shiny bottom full of rusty water. She was a hire boat at the end of the season so she had spent months moving around. She was also regularly blacked. This pitting cannot have been due to any shoreline or stray current erosion

 

Richard

[John V]

My post #44 although flippant actually points to a possible solution (but not one that is popular with narrowboat owners generally)

If the hull is completely coated in an insulating layer for example a thick epoxy layer this would prevent any galvanic corrosion. It would mean that the base plate would have to be coated and that areas subject to constant mechanical abrasion would soon lose there protection but just maybe.......

[bassplayer]

My post #44 although flippant actually points to a possible solution (but not one that is popular with narrowboat owners generally)

If the hull is completely coated in an insulating layer for example a thick epoxy layer this would prevent any galvanic corrosion. It would mean that the base plate would have to be coated and that areas subject to constant mechanical abrasion would soon lose there protection but just maybe.......

Yeah but....if a small area gets scraped off by something on the bottom wouldn't that create an Achilles Heal leading to super corrosion of that spot? I only takes one small hole to sink a boat.

[Traveller]

So we are back to blacking with two-pac?

 

Gourdias, from what you are saying it seems that it is the safety aspect of the 240 vault supply (it must be earthed via the hull) that makes GC a possibility. The sensible approach therefore seems to be to use an extension lead to run the charger or hoover etc on an as and when basis. Obviously the lead should not be left connected and this will not work for those who require a constant hook-up.

Edited November 28, 2014 by Traveller