Hull Corrosion Surveys

[DandGNWales]

We recently rented a Canal Barge on the Llangollen canal and got chatting to a friendly guy in one of the many canal side pubs. turns out he was a Corrosion Engineer for a large Oil Company, and he was asking us if we thought canal boaters would pay a nominal amout (from memory I think it was £4 a foot) for an annual dip cell survey to tell if the anodes are working well enough and providing good protection of the hull. As I am a man of my word and promissed this guy I would ask the question to more experienced hands so I have carried out my promise, so over to you guys for your opinion, he really sold the idea to us and for the nominal costs it sounded like good value and would help us sleep at night knowing our expensive pride and joy was not falling apart as we slept

[PhilR]

We recently rented a Canal Barge on the Llangollen canal and got chatting to a friendly guy in one of the many canal side pubs. turns out he was a Corrosion Engineer for a large Oil Company, and he was asking us if we thought canal boaters would pay a nominal amout (from memory I think it was £4 a foot) for an annual dip cell survey to tell if the anodes are working well enough and providing good protection of the hull. As I am a man of my word and promissed this guy I would ask the question to more experienced hands so I have carried out my promise, so over to you guys for your opinion, he really sold the idea to us and for the nominal costs it sounded like good value and would help us sleep at night knowing our expensive pride and joy was not falling apart as we slept

 

That doesn't sound a nominal amount to me and no I wouldn't think it worthwhile.

[Athy]

That would be £180 per year for our boat, and well over £200 for some members' boats. It sounds a bit on the dear side to me.

[Mac of Cygnet]

I might be interested if I knew what a Dip Cell survey was

[Grace and Favour]

I might be interested if I knew what a Dip Cell survey was

 

clicky

[DandGNWales]

I might be interested if I knew what a Dip Cell survey was

 

I have just spoken with the guy again as he has a boat for sale that we are interested in, and I have got it wrong it's £2 a foot and he tells me you would get a report with all the readings etc, I also asked him what a dip cell survey was, and if i get this bit right, it's the same idea how they test the corrosion prevention measures on the Oil Rig legs, the cell is what they put in the water to measure the output of the anodes, and you test it or dipit at deferent levels hence dip cell survey, I think I got that bit correct. So sorry for the confusion but if we end up buying his boat ( a 56 foot cruiser stern) or another, I think we will take the plunge just for my piece of mind, as I should imagine over plating is very expensive?

 

Thanks for the response I will pass them on to him ( if he sells me his boat for the right price )

[Guest User]

I reckon I'd still be quite happy with ultrasound testing, it's pretty much an accepted part of a pre-purchase survey .... it gives an idea of the metal thickness, and the surveyor can report if there are any localised suspect areas of pitting etc ... if the ultrasound shows that most of the metal is still all there then I'd figure the anodes have probably been doing their job.

Edited September 19, 2009 by Graham!

[DandGNWales]

I reckon I'd still be quite happy with ultrasound testing, it's pretty much an accepted part of a pre-purchase survey .... it gives an idea of the metal thickness, and the surveyor can report if there are any localised suspect areas of pitting etc ... if the ultrasound shows that most of the metal is still all there then I'd figure the anodes have probably been doing their job.

 

I agree, but thats an out of the water survey, this one can be done with the boat in the water, but as we have said, we are new to the canals and narrow boats, so I'm not sure how often you get them out of the water to black them, does every 2 or 3 years sound right?

[Ike]

It's my understanding that a dip cell survey wouldn't actually tell you anything about the condition of the hull, only that of anodes. It's perfectly possible to have brilliant anodes on a hull that was well knackered. If a boat was blacked well, even after three years without anodes I wouldn't expect there to be too much rusting at which point it would be out of the water again anyway.

 

IMHO while very valuable for offshore installations at a greater cost than a days dry docking it really isn't worth it for small inland craft.

[Gibbo]

Am I being cynical again or is this thread............. oh never mind.

 

Gibbo

[NB Willawaw]

Fishing ?

[Gibbo]

Fishing ?

 

Perhaps.............

 

I'm thinking of setting up a business doing (whatever), do you think there would be any call for it at x pounds per foot?

 

Would have been more honest. But what do I know?

 

Gibbo

Edited September 19, 2009 by Gibbo

[DandGNWales]

Perhaps.............

 

I'm thinking of setting up a business doing (whatever), do you think there would be any call for it at x pounds per foot?

 

Would have been more honest. But what do I know?

 

Gibbo

 

No Fishing guys, just telling the truth, if I make a promise to anyone I will always try 110% to fulfill it.

[Graham Bowers]

It's my understanding that a dip cell survey wouldn't actually tell you anything about the condition of the hull, only that of anodes. It's perfectly possible to have brilliant anodes on a hull that was well knackered. If a boat was blacked well, even after three years without anodes I wouldn't expect there to be too much rusting at which point it would be out of the water again anyway.

 

IMHO while very valuable for offshore installations at a greater cost than a days dry docking it really isn't worth it for small inland craft.

I used to do these surveys on ships donkeys years ago, but some of those brain cells survive.

The survey tells you whether your cathodic protection system is effective at the time of the survey by measuring the potential between the hull and a silver / silver chloride half cell that you dangle over the side. Its not snake oil, it is science.

Cheers

Graham

[Ike]

Its not snake oil...

Wasn't trying to suggest it was. Simply trying to make the point that knowing how well the cathodic protection is working is probably far less useful on a fresh water boat that's out of the water every three years than an oil rig in the middle of the North Sea.

[NB Willawaw]

In that case, you can tell your friend that IMHO, narrowboaters will never pay for it because in my experience, they will be reluctant to spend

money on a technique that they don't understand and therefore have no faith in.

 

On a 60ft boat, thats £120. Many of the boaters I know spend less than that on an inverter.

 

My understanding of the technique tells me that it shows if there is enough anode protection on an offshore structure, but the test

is only valid if the structure is in one position. This is not a problem with an offshore structure as they are usually out at sea.

 

Assuming you can get decent readings in fresh canal soup, it will be problematic on a narrowboat because the electrical conditions can change around the boat in a busy marina.

 

The test will only tell you about your anodes and how well they are working at a moment in time. It won't tell you if the damage has already been

done, so is not an in-water alternative to an ultrasonic hull thickness "out of water" survey or visual inspection looking for bright spots or pitting.

 

Incidentally, these tests are already done on salt water yachts with an inexpensive sensitive analogue voltmeter and some reference electrodes.

 

 

 

 

 

No Fishing guys, just telling the truth, if I make a promise to anyone I will always try 110% to fulfill it.

Edited September 19, 2009 by NB Willawaw

[RLWP]

I used to do these surveys on ships donkeys years ago, but some of those brain cells survive.

The survey tells you whether your cathodic protection system is effective at the time of the survey by measuring the potential between the hull and a silver / silver chloride half cell that you dangle over the side. Its not snake oil, it is science.

Cheers

Graham

 

Are you a vet?

 

Richard

[Tony Brooks]

It's my understanding that a dip cell survey wouldn't actually tell you anything about the condition of the hull, only that of anodes. It's perfectly possible to have brilliant anodes on a hull that was well knackered. If a boat was blacked well, even after three years without anodes I wouldn't expect there to be too much rusting at which point it would be out of the water again anyway.

 

IMHO while very valuable for offshore installations at a greater cost than a days dry docking it really isn't worth it for small inland craft.

 

 

Especially as it will confirm is the middle sections of probable the majority of narrowboats have far from optimum and possibly no protection from the anodes at either end (I know some builders fit centre anodes).

[Guest User]

Especially as it will confirm is the middle sections of probable the majority of narrowboats have far from optimum and possibly no protection from the anodes at either end (I know some builders fit centre anodes).

 

... but, if its merely confirming something that would be (easily ?) evidenced by visual inspection of the hull, say when a boat comes out the water for blacking, why the need for a dip test ?

[Graham Bowers]

Are you a vet?

 

Richard

Very good :-)

[dor]

Hang on - have I got this right? you are interested in buying a boat from someone, who is going to do you a "hull survey"? Now some people think I'm a bit on the cynical side, but I think I know what that survey would show.

 

Rule one: Always get a survey done by someone totally independent of the seller.

[mayalld]

Hang on - have I got this right? you are interested in buying a boat from someone, who is going to do you a "hull survey"? Now some people think I'm a bit on the cynical side, but I think I know what that survey would show.

 

Rule one: Always get a survey done by someone totally independent of the seller.

 

No, rule number one is;

 

When a new poster comes on telling you about this service he has heard about, something isn't right.

 

When the same poster comes back the next day with a different price, something is positively not right.