rusting bottom

[Roger & Margaret]

I have a Springer style narrowboat built around 1990, bought 2006 after an ultrasound and 5mm. survey said the hull was between 4.1 and 5mm. Three years later, the bottom plate rusted through near an edge weld, and a piece popped into the boat about 10cm long and up to 3cm wide. Luckily i was looking for a small leak at the time (as there was occasional puddles of water in the bilges) and managed to put some Waterweld into the hole. The boat is now on dry land awaiting a bottom job. Query for the experts, why did it happen?

[denboy]

no expert but i`ll have a stab at it

no anodes fitted or not doing there job

bad 240volt shore line connection

hull being used as a negative return

a boat moored next to yours with bad electrics

all possible

oh and also the survey may not have been as thorough as well

Edited July 26, 2009 by denboy

[alan_fincher]

oh and also the survey may not have been as thorough as well

 

I'm afraid that has got to be favourite, hasn't it ?

 

If an approximately 16 year old boat had really only lost a maximum of less than one millimetre, no way, I would say, is it suddenly going to lose 4 times that amount in the next 3 years.

 

That would mean it had suddenly started losing steel (roughly) over 15 times faster than it was before.

 

I can't believe that the bit that has gone though now was genuinely at least 4.1mm at survey time, I'm afraid.

[Roger & Margaret]

The anodes were still in place, but well used. No shore connections on the boat. The boat was moored on the main line, but in a different location to its usual spot, due to the Mon & Brec breach. On the survey, the report guarantees nothing as they only check at specific points along the hull, 8 "stations" with 8 points down the sides and bottom. makes you wonder if an ultrasound survey is worth it!

[OldGoldy]

and a piece popped into the boat about 10cm long and up to 3cm wide. ............................................. Query for the experts, why did it happen?

Not expert, not even one who works in steel, but maybe imperfection rolled into the plate? What is the thickness of the remaining bottom plate(s) at this time?

[Roger & Margaret]

Looks as if the rest of the hull is OK with minor pitting on the bottom maybe one more place where it is bad but not yet confirmed as the bottom has not been fully cleaned off yet

[Arnot]

I have a Springer style narrowboat built around 1990, bought 2006 after an ultrasound and 5mm. survey said the hull was between 4.1 and 5mm. Three years later, the bottom plate rusted through near an edge weld, and a piece popped into the boat about 10cm long and up to 3cm wide. Luckily i was looking for a small leak at the time (as there was occasional puddles of water in the bilges) and managed to put some Waterweld into the hole. The boat is now on dry land awaiting a bottom job. Query for the experts, why did it happen?

I am at the moment restoring the hull of my ancient narrow boat and for the last few weeks I have been carefully removing all the rust and scale and treating or repairing it as necessary. As well as this I occasionally get called out to pump out sunk or sinking boats and have to find out the cause of the problem.

 

I have to say that from what I have found I really dont think that it would be feasible to be 100% accurate with any form of hull survey in a fitted out boat short of perforating the bottom like a colander. The variables that result in areas of accelerated corrosion are so manifold that I suspect all you can ever get from a surveyor on an older boat is a good indication and it would be unfair to expect more.

 

On my boat that probably started at about 8mm in 1973 (5/16ths?) there are pits of about 2mm in places from both sides. Not a problem except where they co-incide... What was interesting was the pattern of corrosion near to the welds on the inside; very close to the weld the corrosion was at it's worst but about an inch away, the corrosion was at it's least. This left a raised ring round each weld, I can't think why but I'm no mettallurgist (or speeeler) Anyone care to expand?

 

The original ironwork is generally still at it's 1/4" original thickness but behind the knees (no surprise here) is is paper thin in places and for some reason just one side of the plate ajoining the bottom of the stem post had a lace effect when the scale was knocked off.

 

Regards

 

Arnot

[Malarky]

I am at the moment restoring the hull of my ancient narrow boat and for the last few weeks I have been carefully removing all the rust and scale and treating or repairing it as necessary. As well as this I occasionally get called out to pump out sunk or sinking boats and have to find out the cause of the problem.

 

I have to say that from what I have found I really dont think that it would be feasible to be 100% accurate with any form of hull survey in a fitted out boat short of perforating the bottom like a colander. The variables that result in areas of accelerated corrosion are so manifold that I suspect all you can ever get from a surveyor on an older boat is a good indication and it would be unfair to expect more.

 

On my boat that probably started at about 8mm in 1973 (5/16ths?) there are pits of about 2mm in places from both sides. Not a problem except where they co-incide... What was interesting was the pattern of corrosion near to the welds on the inside; very close to the weld the corrosion was at it's worst but about an inch away, the corrosion was at it's least. This left a raised ring round each weld, I can't think why but I'm no mettallurgist (or speeeler) Anyone care to expand?

 

The original ironwork is generally still at it's 1/4" original thickness but behind the knees (no surprise here) is is paper thin in places and for some reason just one side of the plate ajoining the bottom of the stem post had a lace effect when the scale was knocked off.

 

Regards

 

Arnot

Weld could be acting as an annode, (especialy so with iron which is kind of self annoding)!

[Hairy-Neil]

..... makes you wonder if an ultrasound survey is worth it!

 

A good survey is a combination of high tech ultrasound machine and low tech lump hammer.

[PaddingtonBear]

Slightly of topic but somewhat the same tale. Some friends of ours moved from a very normal s/d house in Brighton to a share of an Arts and Crafts manor. They are academics and I am afraid fullfill the popular image to a tee. They decided to have a full survey done by a partner of the biggest and most expensive local surveyors. It cost them nearly £1800 eight years ago and was so surrounded with exclusions that it was worse than useless - no carpets up (there weren't any!!), no visit to loft space as light didnot work (torch?). I got involved when they wanted to fit child locks on the first floor windows. I opened the casement and was luckily holding the stay as it fell out! - all the windows were the same yet there was not mentioned in the survey. No come back what so ever or at least it would have cost them a great deal of money to go to court. They decided to spend it on new windows . The only boat that I have ever had surveyed was our first, a plastic cruiser which we have just sold. We have subsequently spent over £90,000 inc. having just bought big Woolwich 'Chertsey' without recourse to 'surveyors' who in my experience are the as management consultants 'they borrow your watch and tell you the time and then sell it back to you' Trevor Whitling et al totally excused of course.

[Phil Ambrose]

I am at the moment restoring the hull of my ancient narrow boat and for the last few weeks I have been carefully removing all the rust and scale and treating or repairing it as necessary. As well as this I occasionally get called out to pump out sunk or sinking boats and have to find out the cause of the problem.

 

I have to say that from what I have found I really dont think that it would be feasible to be 100% accurate with any form of hull survey in a fitted out boat short of perforating the bottom like a colander. The variables that result in areas of accelerated corrosion are so manifold that I suspect all you can ever get from a surveyor on an older boat is a good indication and it would be unfair to expect more.

 

On my boat that probably started at about 8mm in 1973 (5/16ths?) there are pits of about 2mm in places from both sides. Not a problem except where they co-incide... What was interesting was the pattern of corrosion near to the welds on the inside; very close to the weld the corrosion was at it's worst but about an inch away, the corrosion was at it's least. This left a raised ring round each weld, I can't think why but I'm no mettallurgist (or speeeler) Anyone care to expand?

 

The original ironwork is generally still at it's 1/4" original thickness but behind the knees (no surprise here) is is paper thin in places and for some reason just one side of the plate ajoining the bottom of the stem post had a lace effect when the scale was knocked off.

 

Regards

 

Arnot

 

It may be that the heat generated by welding has effected the chemical make up of the plate. Many years ago there was a fire at Rolls Royce, they decided that all the aero engine parts should be ok as they run at white hot temps.

However when they X-rayed and ultrasound tested the components strange fractures were shown up. It transpired that they were caused by engineers such as myself writing on the nimonic steel with lead pencils, the graphite was absorbed by the metal!! Rolls then had to contact every component supplier to put a stop to this practise. I should add the writing would be calculations and not shopping lists.

 

Phil