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RedsfanUk

Just had survey on potential boat.

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33 minutes ago, Bee said:

I think anodes are only useful near the bronze propeller and associated different metals. The rudder on my boat is pitted and needs more or bigger anodes. Having said that I have had them on my boat from new but I will not replace most of them. Its all about the paint, in my experience paint stops pits deepening and should therefore stop them developing. Steel is steel whether it is made into a skip or a boat and steel + water and oxygen will corrode. The bottom will do exactly the same but is also more likely to corrode from inside as well as water will collect there. Remember the pics of Titanic when it was discovered? Covered in 'rusticles', Total darkness, precious little oxygen and quietly rusting away. Bitumen paint is OK for a year or so but there is better stuff around now and it is the best, if not only, defence against corrosion and docking and painting every two or three years is best. Its not rocket science.

There was a thread a year or so ago that might have yielded some useful information had it not been for the manner in which the new poster with seemingly relevant experience and knowledge set about addressing the forum.

 

What I took from that is that anodes are not just for protection of dis-similar metals. For metals in water or the ground there is a benefit from controlling the potential of the metal. You have to remember that all chemical reactions are essentially an electrical phenomenon.

 

This accords with what @matty40s says above and from my own experience with unprotected structural steels I support what he says. Even in normal open air conditions steel rusts at a very slow rate. Underwater where there is limited oxygen there will still be surface rusting but a far slower rate of corrosion. Go look at the photos of the Titanic again and remind yourself that 73 years had passed between the sinking and the exploration of the wreck. Ask yourself why is it that what is effectively a large steel structure still retains it’s structural integrity. I don’t think the photos bear out your point at all.

 

Pitting is a phenomenon caused by adverse electrical potential, chemical attack or repeated mechanical attack on the same spot. All of which can indeed be prevented by a sound coating system but ironically in some circumstances it’s probably better to have no cover at all than one that has localised damage. In the event of the latter an anode in close proximity will be of benefit. That’s the logic of galvanising.

 

JP

 

 

Edited by Captain Pegg

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40 minutes ago, alan_fincher said:

How old is it?

18 years old, same boat builder as Chalice. ....from JoethePlumbers favourite boatermarket.

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Then of course there is Microbial corrosion which is shown as orange tubercles.

 

https://www.researchgate.net/publication/279529090_Microbiologically_Induced_Corrosion

 

 

http://www.keelblack.co.uk/wp-content/uploads/2017/08/MICROBIOLOGICAL-CORROSION.pdf

Edited by Alan de Enfield

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This is one of my favourite rust links

https://www.sea.museum/2019/01/08/rusticles-and-wrecks

 

As you can see you can get some pretty rust with just steel (no mixed metals) and no coating. They've sped the process up a lot with applying the current intentionally. But is certainly shows why you'd want to be doing something about galvanic isolation for stray current. (And, to my mind, given the facilities and funds to do so, probably coat the bottom of the boat too - there was no aeration of that tank). You can always get them to put a few extra coats at the water line (which I think is where the boat in this thread but obvs in general many) suffer most.

 

Edited to add: there are few posters on here who can tell you abt the most suitable coatings and how to get them applied.

Edited by TheMenagerieAfloat

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1 hour ago, Parahandy said:

Those are incredible figures you are quoting Allan , did the fact that you designed your Boat have part to play in this staggering outlay ? I imagine Gold Leaf Motif can be pretty expensive😀

£34k in 3 years is for me an astounding figure .

No, our design related solely to the interior layout.

 

The main items of expense were that first it needed a total repaint, then the next year a new engine, gearbox and stern gear, and then suddenly over the next year the sides went from almost perfect to almost nothing below the waterline and had to be replated.

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2 minutes ago, Keeping Up said:

then suddenly over the next year the sides went from almost perfect to almost nothing below the waterline and had to be replated.

Did you come up with any reason for the acceleration in deterioration? I know surveyors sonetimes do a rough estimate of the rate of corrosion based on original and current thicknesses with a view to how it is likely to continue to rust but that assumes a more or less constant rate of deterioration... 

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5 minutes ago, Keeping Up said:

No, our design related solely to the interior layout.

 

The main items of expense were that first it needed a total repaint, then the next year a new engine, gearbox and stern gear, and then suddenly over the next year the sides went from almost perfect to almost nothing below the waterline and had to be replated.

Incredible Allan especially such a decline in the sides , I think I recall you moored up somewhere local , Stoke Hammond I think ? Possibly someone else .

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2 hours ago, TheMenagerieAfloat said:

Did you come up with any reason for the acceleration in deterioration? I know surveyors sonetimes do a rough estimate of the rate of corrosion based on original and current thicknesses with a view to how it is likely to continue to rust but that assumes a more or less constant rate of deterioration... 

Have you seen a surveyor try to claim they can calculate such? I wouldn’t take much notice. The stating of plate thicknesses to 0.1mm is nonsense. It’s just the meter gives it to that level and folks love to believe something that looks definitive. I think it’s pretty meaningless to work to anything less than the nearest millimetre. There’s no significant loss of plate thickness in the above example. The surveyor above does at least seem to have some recognition of what they are actually measuring. Although I’m sure the meter they used was trying to establish the position of the true effective back of the plate concerned there is indeed a degree of trickery involved in the meter converting that into a supposedly precise measurement.

 

Ultrasonic testing works by sending a pulse into the test piece and measuring the time taken for the pulse to return to the test meter. The signal returns because it is reflected by any discontinuities it encounters in the test piece. In the case of a new steel plate the reflected signal should return as a short sharp peak of similar overall magnitude to what was transmitted having been reflected off the well defined rear face of the plate. When testing a used plate that has a rusted back surface - and potentially a meter that’s reading through coatings on the front face - the signal received back by the test piece will be wider and flatter and will have lost some of the signal that has been reflected off at an angle. What the meter does is converts the signature of the multiple signals it receives into a distance using an algorithm in its programming. What modern meters have isn’t better testing capabilities but better algorithms to calculate the thickness which enables them to process more ambiguous data into something usable (but not necessarily more accurate) than was previously possible.

Plate thickness is nominal and has tolerances that are significantly more than +/-0.1mm. A nominal 10mm plate will not necessarily measure 10.0mm when new. The thickness also varies so putting a test meter on a new plate you will find variation of 0.1s of millimetres as the test meter is moved around the plate.

 

So unless you have a series of test results from new taken at the same points on the hull, using the same type of meter, and have evidence the meters are calibrated then it’s probably not worth the piece of paper its written on. Testing a narrowboat is probably not so complex that I’d also add in to the above list a standardised operator training regime.

 

All you need to know is that if your plate isn’t losing thickness measured in whole millimetres in timescales measured in years rather than decades then all is well. You don’t need need a fancy meter and a calculator to know that.
 

Technology - like the internet - gives people apparent knowledge without the necessary understanding. Thankfully I can ask a number of industry experienced metallurgists and material scientists about these things rather than relying on the internet to tell me what a 25 year old suffering from chronic academia has said in words that in all probably I don’t understand in response to a loaded question posed by a client with a vested interest and brandishing the funding necessary to get said academic their PhD (for this is how those research papers come into being folks).


JP


ETA gender neutrality because I don’t know the surveyor was a man 😂

Edited by Captain Pegg
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Nobody managed to come up with a satisfactory explanation for the sudden deterioration in the . We had the boat surveyed before buying a new engine, and all was fine (6mm sides, no pitting greater than 0.5mm) then 18 months later the whole of each side had thousands of pits that were between 4 and 5 mm deep. The two main candidates were either a fault on the mains supply to our mooring (yes that is Stoke Hammond, but we've sub-let it for the time being) which the electricity supplier admits did exist for 3 months but they say it couldn't have been responsible, or else a DC issue when the new engine was fitted that caused some of the charging current to ignore the nice fact short negative lead that I gave it and instead to travel via the exhaust pipe to the hull.

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@Captain Pegg's boat is most likely to sink under the weight of the chip on his shoulder... No, no one has claimed to calculate such a thing... Just the rough idea that  nothing has happened at an alarming rate over the last few decades and so it should be good for a few more. Exactly the kind if useful translation for the lay person you'd hope for. Light conversation to explain to a novice, not something you right in a report! 

 

What is interesting about @Keeping Up's situation is that it was fine for decades and then suddenly the rate changed very dramatically.

18 minutes ago, Keeping Up said:

Nobody managed to come up with a satisfactory explanation for the sudden deterioration in the . We had the boat surveyed before buying a new engine, and all was fine (6mm sides, no pitting greater than 0.5mm) then 18 months later the whole of each side had thousands of pits that were between 4 and 5 mm deep. The two main candidates were either a fault on the mains supply to our mooring (yes that is Stoke Hammond, but we've sub-let it for the time being) which the electricity supplier admits did exist for 3 months but they say it couldn't have been responsible, or else a DC issue when the new engine was fitted that caused some of the charging current to ignore the nice fact short negative lead that I gave it and instead to travel via the exhaust pipe to the hull.

Do you mind me asking (appreciate this might not be favourite topic in the circs!) what kind of galvanic protection (isolator? annodes? ) you had at the time. 

Edited by TheMenagerieAfloat

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2 hours ago, Alan de Enfield said:

Whilst on the subject - I'll post this (again)

 

It shows what happens, why and how in simple words;

 

http://roscoemoss.com/wp-content/uploads/publications/fmcf.pdf

Er, Simple words? It appears that I was wrong. It is rocket science.  There is more going on than I thought but what to do about it? For those of us with steel boats we know that above the waterline steel is brilliant so long as it is painted and looked after. What is happening underwater is interesting and very dfferent.  Bacteria, calcium stuff and nasty black anaerobic goings on in pits as well as good old 'rust'. Hopefully two or three coats of epoxy paint will foil the chemistry. Still not sure about anodes, I wonder if they would be more effective at protecting bigger areas if they were made in metre long strips instead of big lumps?

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14 minutes ago, TheMenagerieAfloat said:

No, no one has claimed to calculate such a thing... Just the rough idea that  nothing has happened at an alarming rate over the last few decades and so it should be good for a few more.

That is a possible assumption if the circumstances remain identical.

 

However move the boat to different waters, plug into a different bollard, do some work on your electrics, power supply authority do some work on their bollards etc etc and the speculation (suggestion) becomes redundant.

 

As most of us move our boats then I cannot see how any suggestion that it will do what it did for the last X year is not flawed.

Edited by Alan de Enfield

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35 minutes ago, Keeping Up said:

Nobody managed to come up with a satisfactory explanation for the sudden deterioration in the . We had the boat surveyed before buying a new engine, and all was fine (6mm sides, no pitting greater than 0.5mm) then 18 months later the whole of each side had thousands of pits that were between 4 and 5 mm deep. The two main candidates were either a fault on the mains supply to our mooring (yes that is Stoke Hammond, but we've sub-let it for the time being) which the electricity supplier admits did exist for 3 months but they say it couldn't have been responsible, or else a DC issue when the new engine was fitted that caused some of the charging current to ignore the nice fact short negative lead that I gave it and instead to travel via the exhaust pipe to the hull.

Lovely mooring down there Allan which I have been after buying for Years , I did wonder where you had gone .

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4 minutes ago, Alan de Enfield said:

That is a possible assumption if the circumstances remain identical.

 

However move the boat to different waters, plug into a different bollard, do some work on your electrics, power supply authority do some work on their bollards etc etc and the speculation (suggestion) becomes redundant.

 

As most of us move our boats then I cannot see how any suggestion that it will do what it did for the last X year is not flawed.

Obviously things change. But they dont usually change dramatically enough for surprise changes - @Keeping Up's experience is not that common.

 

Moving ones boat around a lot would tend to help with a smoother rate... If, e.g. it had been off grid for 20years touring the cannals and one intends to do likewise no given local conditions are going to have time to do much to change the average over the next 20yrs.

 

Obviously if it goes from being off grid to on shore power/being more or less permanently in one marina to another or something that isn't goi g to hold, no, I agree

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21 minutes ago, TheMenagerieAfloat said:

Moving ones boat around a lot would tend to help with a smoother rate... If, e.g. it had been off grid for 20years touring the cannals and one intends to do likewise no given local conditions are going to have time to do much to change the average over the next 20yrs.

There is a huge difference in the water quality / contamination between (say) the Llangollen and the BCN

 

Which is why C&RT have to pay so much to dispose of the "controlled waste" (contaminated dredgings)

 

Extract from the C&RT website

 

Dredging is basically scooping up the sediment from the bottom of the waterways and removing it. As the equipment is cumbersome to move, a significant portion of the cost of the work is to get the tools to site. However, the majority of the cost of dredging comes when we have to dispose of the waste in an environmentally friendly way.

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1 hour ago, TheMenagerieAfloat said:

 

What is interesting about @Keeping Up's situation is that it was fine for decades and then suddenly the rate changed very dramatically.

Do you mind me asking (appreciate this might not be favourite topic in the circs!) what kind of galvanic protection (isolator? annodes? ) you had at the time. 

There was a galvanic isolator, fully tested regularly - unlike one of the boats on the same supply which had no isolator but suffered no such damage - and there were 3 anode each side (bow stern and midpoint) which appeared to have had no influence at all as there was the same pitting very close to them.

 

I think my experience was unusual, but not unique (my surveyor had personally seen one other such case the previous year). The only useful lessons I think are (1) boats are always expensive but sometimes unexpectedly so and (2) if a survey says all was ok a couple of years ago, in the intervening time the boat could have turned into a colander so if you are buying one you must get a fresh one.

 

I was lucky that my insurer insisted on a survey when the boat was 25, otherwise we wouldn't have known and soon afterwards we would suddenly have become the proud owners of a submarine.

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1 hour ago, TheMenagerieAfloat said:

@Captain Pegg's boat is most likely to sink under the weight of the chip on his shoulder... No, no one has claimed to calculate such a thing... Just the rough idea that  nothing has happened at an alarming rate over the last few decades and so it should be good for a few more. Exactly the kind if useful translation for the lay person you'd hope for. Light conversation to explain to a novice, not something you right in a report! 

If you stick about you’ll see this same topic crops up two or three times every year and the same misconceptions and articles - probably understood by nobody including the poster - get trotted out. We never seem to move forward in the collective understanding and to me it’s a subject which generates a degree of unnecessary worry within the narrow boating community.

 

My post was triggered by your comments rather than in direct response. Folks have done that sort of calculation on the forum hence I asked if you had seen the same from a surveyor.

 

I’m still of the view a rough calculation has the potential to be misleading for the reasons AdE gives and Keeping Up’s experience demonstrates. It’s mostly just something you have to deal with at the moment in time it presents itself.


If my boat sinks it will actually be because it’s 52 years old, the hull was fabricated from 1/4” and 1/6” steel and was overplated 33 years ago. I also understand that I’ll get some warning of impending doom and will probably be able to do something it, and if not it’ll sink in two feet of water and nobody will die. Until it happens I’ll just do the obvious and enjoy my boating in spite of the list the chip induces.

 

JP
 

 

 

 

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21 hours ago, TheMenagerieAfloat said:

Have you seen the boat/ad for it?

I wondered that but, given that  it was Alan, (de Enfield), I was reasonably sure that he would have seen the ad or a quote of the asking price, and that I had missed it :) 

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2 minutes ago, Captain Pegg said:

 


If my boat sinks it will actually be because it’s 52 years old, the hull was fabricated from 1/4” and 1/6” steel and was overplated 33 years ago. I also understand that I’ll get some warning of impending doom and will probably be able to do something it, and if not it’ll sink in two feet of water and nobody will die. Until it happens I’ll just do the obvious and enjoy my boating in spite of the list the chip induces.

 

JP
 

 

 

 

1/4" & 3/16" maybe? That used to be pretty common back then. The other perennial subject on here is overplating and the fact that you had that done 30+ years ago should give people something to think about.  Overplating is sometimes condemned as being the devils work and a potential disaster but most of us are not crossing the North Atlantic in a winter storm and I reckon that a repair that lasts 33 years is pretty good.

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2 minutes ago, Bee said:

1/4" & 3/16" maybe? That used to be pretty common back then. The other perennial subject on here is overplating and the fact that you had that done 30+ years ago should give people something to think about.  Overplating is sometimes condemned as being the devils work and a potential disaster but most of us are not crossing the North Atlantic in a winter storm and I reckon that a repair that lasts 33 years is pretty good.

Dunno. I’d have to check the steelwork schedule. The fact I’ve got that tells something about the provenance and past ownership of the boat. Although I don’t know the absolute reason it was overplated I know that it was done by the person who fabricated the original steelwork and I suspect it was not a repair to any defect.


It does though colour my view of some of the comments regarding overplating.

 

JP

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2 hours ago, Keeping Up said:

There was a galvanic isolator, fully tested regularly - unlike one of the boats on the same supply which had no isolator but suffered no such damage - and there were 3 anode each side (bow stern and midpoint) which appeared to have had no influence at all as there was the same pitting very close to them.

 

I think my experience was unusual, but not unique (my surveyor had personally seen one other such case the previous year). The only useful lessons I think are (1) boats are always expensive but sometimes unexpectedly so and (2) if a survey says all was ok a couple of years ago, in the intervening time the boat could have turned into a colander so if you are buying one you must get a fresh one.

 

I was lucky that my insurer insisted on a survey when the boat was 25, otherwise we wouldn't have known and soon afterwards we would suddenly have become the proud owners of a submarine.

What rotten luck* - glad you have a sense of humour about it though! 

 

*where luck is an unidentifed cause, a known unknown, for the pedants

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7 hours ago, Bee said:

1/4" & 3/16" maybe?

Yep. You were right. A shade under 5mm. I suspect the original plate thicknesses were why it was overplated as from what I can gather it was seen as a positive thing at the time it was done.

 

JP

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On 15/02/2020 at 12:58, Keeping Up said:

There was a galvanic isolator, fully tested regularly - unlike one of the boats on the same supply which had no isolator but suffered no such damage - and there were 3 anode each side (bow stern and midpoint) which appeared to have had no influence at all as there was the same pitting very close to them.

 

I think my experience was unusual, but not unique (my surveyor had personally seen one other such case the previous year). The only useful lessons I think are (1) boats are always expensive but sometimes unexpectedly so and (2) if a survey says all was ok a couple of years ago, in the intervening time the boat could have turned into a colander so if you are buying one you must get a fresh one.

 

I was lucky that my insurer insisted on a survey when the boat was 25, otherwise we wouldn't have known and soon afterwards we would suddenly have become the proud owners of a submarine.

Sounds awfully like your boat corroded preferentially to protect them. How close were you to the other boat? Was it on the end of a string of boats, or next to you?

Your boat acted, possibly due to positioning (relative distance from connection, proximity to earth, something like that), as an anode for that boat.

 

Out of curiosity, I tested the hull of our barge (since sold) vs the river water. 20V difference.
A galvanic isolator was purchased, fitted - insignificant difference.

 

 

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59 minutes ago, Alastair said:

Out of curiosity, I tested the hull of our barge (since sold) vs the river water. 20V difference.

A galvanic isolator was purchased, fitted - insignificant difference.

 

 

May I ask how you measured this?  thanks!

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