Talpidae: problems,

[alan_fincher]

Amazing deduction!! Rusting IS a chemical process, corrosion may be a chemical and/or an electrical process.

So from the pictures, and the information gathered so far, what is your best guess at the cause of Ade's woes, please, Chris ?

 

It sounds like he is very rarely landline connected. Can a situation be dreamed up where he is the victim of boats he is moored between that are ?

 

If so, is what's happened avoidable, and how ?

 

I'm sure anybody on pontoon moorings, surrounded by permanently connected boats is interested in understanding what can happen, and what can be done to minimise risk.

[chris w]

So from the pictures, and the information gathered so far, what is your best guess at the cause of Ade's woes, please, Chris ?

 

It sounds like he is very rarely landline connected. Can a situation be dreamed up where he is the victim of boats he is moored between that are ?

 

If so, is what's happened avoidable, and how ?

 

I'm sure anybody on pontoon moorings, surrounded by permanently connected boats is interested in understanding what can happen, and what can be done to minimise risk.

I just wonder whether somehow the hull IS being used (inadvertently) as a return wire. Such a situation, inter alia, would cause the type of "random" corrosion seen.

 

Chris

[Gibbo]

I know OP said his electrical system was isolated from the hull.

 

Obviously I can't be certain on this without seeing it up close and taking some measurements but I don't think it is. I think there are some inadvertent connections on the DC system that are using the hull as a return current path.

 

I also think the prop has been electroplated with steel from the hull or a coating of anode material. It's very difficult to tell from the photos.

 

It needs looking at properly, pronto.

 

I was often called in to troubleshoot boats like this and it was always electrically induced. I think I have considerably more knowledge and experience than another poster on here who reckons electricity has got nothing to do with it. In fact I know I have.

 

A "view" is just that. An opinion based on nothing but gut feeling. No known facts, no known experimental data, no studying and no experience. And it's probably wrong.

 

Some people confuse "theory" with "hypothesis". In any event they are not hypotheses. They are known, proven facts.

 

I carried out an experiment many years ago less than 500 yards from a certain poster's mooring. Two pieces of the same steel, same size, same thickness. Both submerged in the canal. One bonded to the pilings direct, one bonded via a galvanic isolator. After 4 years the directly bonded one had lost over 50%. The other one was still there last time I checked about 4 years later at about 80%. Those are facts, not empty opinions.

 

I would recommend OP doesn't listen to someone living in the 19th century and instead takes advice from someone who actually knows about the subject.

 

Take note that mooring against pilings, with bare metal touching the pilings, can have exactly the same effect as having a bonded shorepower earth and no galvanic isolator or isolation transformer.

 

Gibbo

[Guest]

I know OP said his electrical system was isolated from the hull.

 

Obviously I can't be certain on this without seeing it up close and taking some measurements but I don't think it is. I think there are some inadvertent connections on the DC system that are using the hull as a return current path.

 

I also think the prop has been electroplated with steel from the hull or a coating of anode material. It's very difficult to tell from the photos.

 

It needs looking at properly, pronto.

 

I was often called in to troubleshoot boats like this and it was always electrically induced. I think I have considerably more knowledge and experience than another poster on here who reckons electricity has got nothing to do with it. In fact I know I have.

 

A "view" is just that. An opinion based on nothing but gut feeling. No known facts, no known experimental data, no studying and no experience. And it's probably wrong.

 

Some people confuse "theory" with "hypothesis". In any event they are not hypotheses. They are known, proven facts.

 

I carried out an experiment many years ago less than 500 yards from a certain poster's mooring. Two pieces of the same steel, same size, same thickness. Both submerged in the canal. One bonded to the pilings direct, one bonded via a galvanic isolator. After 4 years the directly bonded one had lost over 50%. The other one was still there last time I checked about 4 years later at about 80%. Those are facts, not empty opinions.

 

I would recommend OP doesn't listen to someone living in the 19th century and instead takes advice from someone who actually knows about the subject.

 

Take note that mooring against pilings, with bare metal touching the pilings, can have exactly the same effect as having a bonded shorepower earth and no galvanic isolator or isolation transformer.

Gibbo

I believe that my boat was showing early signs of such corrosion last time we dry docked (we have no shore power). I have deployed a load of tyres along the pilings with a hope to reducing the effect.

[alan_fincher]

Moley's boat is moored in a small cluster of boats, on pontoons sticking out across the cut at (I would estimate) about 45 degrees to the bank.

 

So he is moored against a pontoon on one side, (I'd guess shared with another boat), and (I think) another boat on the other.

 

I would have thought any exterior electrical effects were from other boats, rather than metal piling at the bank.

 

I can't get my brain around this, but if he's not electrically connected to shore, or the other boats, (fenders in between), then it seems to me the only electrical interaction is via impurities in the water.

 

The suggestion would seem to be that he could be moored in the "electrolyte" of a large "battery" formed between boats either side of him, that may be otherwise electrically connected to each other by their shore-power.

 

I'm quite happy to be told that's a load of b****cks, but I'm sure everybody who moors in such a situation (as many of us must) would like to understand what is, and is not possible.

 

I'm far from convinced that that's what's gone on here, though.

[MoominPapa]

I know OP said his electrical system was isolated from the hull.

 

Obviously I can't be certain on this without seeing it up close and taking some measurements but I don't think it is. I think there are some inadvertent connections on the DC system that are using the hull as a return current path.

 

I also think the prop has been electroplated with steel from the hull or a coating of anode material. It's very difficult to tell from the photos.

 

It would be very interesting to see the results of measuring the voltage between the engine block and the hull, and how the voltage changes as loads are switched on and off. It still seems to me that not having the hull bonded to negative makes the boat only one leakage path from battery positive to hull away from exactly to sort of propeller plating and hull erosion thats shown in the photos.

 

MP.

[Gibbo]

It would be very interesting to see the results of measuring the voltage between the engine block and the hull, and how the voltage changes as loads are switched on and off. It still seems to me that not having the hull bonded to negative makes the boat only one leakage path from battery positive to hull away from exactly to sort of propeller plating and hull erosion thats shown in the photos

 

Yes that's exactly what I'm thinking.

 

A positive grounded hull is lethal for stray current corrosion.

 

An isolated hull is so easy to accidentally turn into a positive grounded hull and no one will be any the wiser.

 

Gibbo

[alan_fincher]

It still seems to me that not having the hull bonded to negative makes the boat only one leakage path from battery positive to hull away from exactly to sort of propeller plating and hull erosion thats shown in the photos.

 

MP.

But if we assume the boat has good and effective isolators in place, and that Ade turns these off when the boat is unattended, then I'm guessing only a very small part of it's life since the last blacking will have had the 12v power connected in any way ?

 

It seems to me if the damage is electrically related, and severe, we need something that is connected most of the time, not just for a tiny percentage of the time.

 

Of course if the isolator(s) is/are left on to power some onboard equipment like an automatic bilge pump, then damage being 12 volt related becomes more likely.

[Moley]

Ok, thanks people, I've just got back from a long day re-stuffing stern gland and all manner of other sh!tty jobs and I'm knackered.

 

I've skimmed through today's postings but nead to re-read before I can comment, it looks like there's some good stuff there.

 

However, you asked for anodes, here are my anodes:

http://i20.photobucket.com/albums/b204/Mol...ck/09022201.jpg

http://i20.photobucket.com/albums/b204/Mol...ck/09022205.jpg

http://i20.photobucket.com/albums/b204/Mol...ck/09022203.jpg

http://i20.photobucket.com/albums/b204/Mol...ck/09022204.jpg

 

In an attempt to clarify a couple of things, our boat isn't liveaboard, it's for weekends and holidays.

 

Alan's quite right, we moor in a small cut-out:

 

 

From the top:

1. Where Tetty should be

Pontoon

2. Talpidae

3. Bronwyn

Pontoon

4. That's Stourbridgeguy's boat but he's moved on, position vacant.

5. Now occupied by Just Heaven

Pontoon

6. Too small to be of any use and certainly couldn't get anyhing in there since Just Heaven's arrived.

 

I think Alan could be right and the engine's earthing through the exhaust, there is certainly a connection somewhere, I've checked it with a meter today, but I need to clarify this for myself.

 

My steelwork is not being used as a return wire. I know precisely what every wire does, where it comes from and where it goes to. All negative returns go directly to leisure bank -ve. The only thing that returns to the crankcase stud where the main engine -ve to starter battery attaches is the bilge pump and that's only used for a few minutes very occasionally.

 

Putting things into context though, let's say we use the boat for 5 weeks of the year:

 

For 5 weeks of the year our boat is away from home moorings, all 12v systems are active, no mains is used.

 

For 47 weeks of the year our boat is on home moorings, she's dead in the water, 12v systems are off, battery isolation keys are removed. There is no metal-to-metal contact, fenders are down between steel and wood. Shoreline is hardly ever connected, I would estimate that in the last 12 months, shoreline has been connected for less than 36 hours.

 

Other than by leaving it too long between blackings, I fail to see how I could be responsible for this.

[cheshire~rose]

Been away this weekend and only just had a chance to catch up with this thread and look at the photo's

 

So sorry to hear about the problems but as others have said try and stay positive until you have the hull survey done because it may not appear as bad as it at first seems. You can add my name to the very long list of those who are rooting for you (or should that be routing?)

[Big Steve]

If that lump I thought was an anode, isn't, then were are they? Everyone else seems to be able to see them, but I've had a good look at those pictures and I can't see any. Help!

[chris w]

My steelwork is not being used as a return wire. I know precisely what every wire does, where it comes from and where it goes to. All negative returns go directly to leisure bank -ve. The only thing that returns to the crankcase stud where the main engine -ve to starter battery attaches is the bilge pump and that's only used for a few minutes very occasionally.

Do you have a radio aerial fitted to the roof? If so, the braid of the coax cable at the roof MUST be cut and the gap bridged with a 470nF capacitor. this will allow radio signals to cross the gap but not DC current.

 

If you don't cut the braid then your hull is acting as a return path. You can check this by disconnecting the hull negative connection and measuring the resistance between the disconnected negative and the hull. It should show an open-circuit if the hull is isolated and a short circuit if it is not.

 

Chris

[NB Alnwick]

Ade,

 

Sorry to hear about your unpleasant surprise - I shall be watching this thread closely to see what the reasons and results are. I do sincerely hope that it turns out to be less of a problem than you think . . .

 

Best Wishes,

Graham

[Ange]

Ade

 

Just to let you know we're thinking of you and hoping the problem isn't as bad as you fear.

 

Ange

x

[bag 'o' bones]

Back to the original topic ahem...

 

Sand blast the affected areas and spray weld?

 

Never heard of it being done on a boat but there is always a first time.

 

Google 'spray weld' or 'metal spraying' and take a look.

 

Saw it being performed on the wasted frames (due to localised pitting) of a steam locomotive some years ago and was very impressed with the results.

 

I've no idea how much it costs but I imagine its cheaper than a re-plate.

Edited February 23, 2009 by bag 'o' bones

[Moley]

Anodes brought up for Big Steve:

 

Well they would have been, why can't I see the pics by adding tags?

Can anybody else get those pics?

 

No, I don't have a radio aerial.

 

It's Tetty and Bronwyn which are permanently connected to their shorelines, Tetty's owners have sold their UK home and now spend most of their year in South Africa and a few months back here cruising the system.

 

I need to try to contact their key holder to see if we can find out what equipment is connected.

 

I'm rather hoping that Trev the Rev might read this and advise what is connected on Bronwyn.

 

To prevent boats swinging around from passing traffic, Mick from Tetty does lash our centre lines and bow lines together across the pontoon. Could it be possible to create an electrical circuit that way, through (frequently damp) polypropylene?

[RobinJ]

So from the pictures, and the information gathered so far, what is your best guess at the cause of Ade's woes, please, Chris ?

It sounds like he is very rarely landline connected. Can a situation be dreamed up where he is the victim of boats he is moored between that are ?

If so, is what's happened avoidable, and how ?

I'm sure anybody on pontoon moorings, surrounded by permanently connected boats is interested in understanding what can happen, and what can be done to minimise risk.

Even in situations where the boat hull is completely isolated from anything on board or on land you can still get electrolysis.

To understand this you have to take an extreme example - standing under a tree in a storm.

Electricity always takes the path of least resistance, so you also need need to look at are the pontoons metal, are they earthed? What other sources could there be in the vicinity, it might not be a boat causing the problem!

This would be particularly relevant if the corrosion was only on one side?

Is it my imagination or is it worse at the meeting of the base plate and the side?

Is there a chance you have been sat on something?

(You'll be surprised at the number of underwater cables).

[Bones]

I have nothing constructive to add to the comments thus far, but I thought I would post something...!

 

Sorry to hear about all this Moles, I hope the survey gives you some clear and concise answers about why on earth this has happened, I cant imagine what it must be like for you all!!!!!

 

So... hugs from down south to you, and lots of thoughts and supportive vibes being sent your way.

 

Xx

[Scotty]

If that lump I thought was an anode, isn't, then were are they? Everyone else seems to be able to see them, but I've had a good look at those pictures and I can't see any. Help!

 

[Gibbo]

If the boat is always moored the same way round, and if the corrosion is worse on one side than the other then I can think of one way this could be caused as a result of other boats/pontoons.

 

Other than that, I don't see how it's possible.

 

Gibbo

[Scotty]

It's Tetty and Bronwyn which are permanently connected to their shorelines, Tetty's owners have sold their UK home and now spend most of their year in South Africa and a few months back here cruising the system.

 

I need to try to contact their key holder to see if we can find out what equipment is connected.

 

I'm rather hoping that Trev the Rev might read this and advise what is connected on Bronwyn.

It would be interesting to see the condition of the neighbouring boat's hulls.

Maybe it's 'something in the water' ?

Perhaps those with shorelines connected are even worse?

 

I know if my boat was moored there i'd want it checked pronto.

 

Hopefully the surveyor can provide some answers

[Trev The Rev]

I'm rather hoping that Trev the Rev might read this and advise what is connected on Bronwyn.

 

To prevent boats swinging around from passing traffic, Mick from Tetty does lash our centre lines and bow lines together across the pontoon. Could it be possible to create an electrical circuit that way, through (frequently damp) polypropylene?

 

Hi Ade - Sorry to hear of your worries.

Bronwyn has no shore electrics actually fitted to the boat at all - We remain hooked up but any equipment we use is free standing, self contained and well isolated from the boat.

 

The only connection to the boat itself is for a free standing battery charger, but then only once or twice a year and then only for 24 hours or so to give batteries a boost over winter, it sits in my garage at home the rest of the time. A circuit through a battery charger can occur, but is rare on modern plastic double insulated chargers, some old metal ones have the -ve 12V charge lead connected to the earth of the charger case and so to the mains earth, but even that is rare.

 

I looked at my anodes just before Christmas and they seemed to be surviving extreemly well. Three years old now.

 

No idea at all about the set up on Tetty. I think they might have said they keep a trickle changer on (but please do not quote me as I'm not sure).

 

I used to be an electrical engineer and have always been aware and protective of possible problems.

I have also considered the problems of the Electrical instalation directly opposite our boats. A hugh transformer station which supplies most of the centre of Kidderminster with power. There could well be some serious ground currents nearby, some of which may well flow through our boats. You normally moor the same way around each time, is the problem more pronounced on any particular side or end.

 

It would appear that you have metal deposits on the stern end (prop etc) is the pitting (erosion) worse on the bow end?

 

I would not think that Tetty's ropes would cause the problems you are indicating. Even when wet the current would be very restricted. Although Metal chains used to secure a boat, will effectively short out its Galvanic Isolator (if fitted).

 

Hope your news is better when surveyed.

Our own boat is due out of the water this year, fingers crossed.

 

Trevor

[andywatson]

If the boat is always moored the same way round, and if the corrosion is worse on one side than the other then I can think of one way this could be caused as a result of other boats/pontoons.

 

Other than that, I don't see how it's possible.

 

Gibbo

 

Although my boat is seldom connected to the shoreline and I am insulated by fenders etc, other boats near me have their 240V landlines continuously in use.

 

Should I be concerned?

[Gibbo]

Although my boat is seldom connected to the shoreline and I am insulated by fenders etc, other boats near me have their 240V landlines continuously in use.

 

Should I be concerned?

 

A few people have PM'd me about this so I'll stick a little anecdote up here.

 

Many years ago I was called out to check a boat that had been suffering serious underwater corrosion. Far more than would be expected. The owner had some replating done but had heard electrical problems could cause this so got me to have a look.

 

I went out with my test equipment and had a poke around. The boat was moored bow in to the banking on parallel moorings. The boat had no shorepower facility.

 

I could find nothing at all wrong with the electrical installation. I asked the owner about the replating and apparently it had nearly all been on one side which the welder thought a bit odd and made him suspect electrical problems.

 

I stuck some copper plates on some meter leads and dangled them over the edge of the boat. The further I moved them away from the boat the higher the voltage I read. A bit more investigation showed the boat on one side (the side where the corrosion had arisen) was at zero volts with respect to ground as it should be. The boat on the other side was at 13.5 volts with respect to ground!

 

An internal fault in this boat had connected the charger +VE output to the hull and the charger -VE to the incoming shorepower earth. This put float charge voltage on the hull. The hull of this faulty boat was seriously pitted but the owner seemed blissfully unaware until it was pointed out to him (he later had to have a full replate on a 10 year old boat).

 

The current from this boat was passing (partially) horizontally across to my client's boat, through his hull (which had no shore earth connection) then out the other side into another boat that did have earth connection. The side next to the faulty boat was ok, the other side had serious corrosion.

 

Three points arise from this:-

 

1. If boats either side of yours have different voltages on them, current can pass through yours and erode your hull.

 

2. If the faulty boat had the incoming shore earth bonded to the hull (which it should be) then the fault could not have arisen as a fuse would have blown somewhere.

 

3. If my client's boat had shorepower with a bonded earth this too would have prevented it happening.

 

My client did talk about suing the other boat owner but I have no idea whether he actually did so.

 

Gibbo

[andywatson]

A few people have PM'd me about this so I'll stick a little anecdote up here.

 

Many years ago I was called out to check a boat that had been suffering serious underwater corrosion. Far more than would be expected. The owner had some replating done but had heard electrical problems could cause this so got me to have a look.

 

I went out with my test equipment and had a poke around. The boat was moored bow in to the banking on parallel moorings. The boat had no shorepower facility.

 

I could find nothing at all wrong with the electrical installation. I asked the owner about the replating and apparently it had nearly all been on one side which the welder thought a bit odd and made him suspect electrical problems.

 

I stuck some copper plates on some meter leads and dangled them over the edge of the boat. The further I moved them away from the boat the higher the voltage I read. A bit more investigation showed the boat on one side (the side where the corrosion had arisen) was at zero volts with respect to ground as it should be. The boat on the other side was at 13.5 volts with respect to ground!

 

An internal fault in this boat had connected the charger +VE output to the hull and the charger -VE to the incoming shorepower earth. This put float charge voltage on the hull. The hull of this faulty boat was seriously pitted but the owner seemed blissfully unaware until it was pointed out to him (he later had to have a full replate on a 10 year old boat).

 

The current from this boat was passing (partially) horizontally across to my client's boat, through his hull (which had no shore earth connection) then out the other side into another boat that did have earth connection. The side next to the faulty boat was ok, the other side had serious corrosion.

 

Three points arise from this:-

 

1. If boats either side of yours have different voltages on them, current can pass through yours and erode your hull.

 

2. If the faulty boat had the incoming shore earth bonded to the hull (which it should be) then the fault could not have arisen as a fuse would have blown somewhere.

 

3. If my client's boat had shorepower with a bonded earth this too would have prevented it happening.

 

My client did talk about suing the other boat owner but I have no idea whether he actually did so.

 

Gibbo

 

Thanks for that informative reply which raises a few more questions about testing for this situation and protecting against resultant corrosion.

 

1 If an adjacent boat has an RCD on it's power bollard would this not have tripped if such a fault occurs?

 

2 If a nearbye boat has such a fault will it show as 12V if a meter is put across hull to hull or hull to earth or hull to pilings?

 

3 Would you recommend earthing your boat either by using the shore line or coupling to the piling to protect against corrosion by other boats?

Edited February 23, 2009 by andywatson