Silt rotting hull base plate

[Blue Angel]

I have just found that my base plate has deteriorated by 2.5mm over 12 months. I have the right number of anodes, but the Marina where I'm based is stilted up to the max. Does anyone know if silt would help erode the base plate please, and can I do anything about it legally?

Edited April 30, 2020 by Blue Angel
Spelling mistake

[mrsmelly]

3 minutes ago, Blue Angel said:

I have just found that my base plate has deteriorated by 2.5mm over 12 months. I have the right number of anodes, but the Marina where I'm based is stilted up to the max. Does anyone know if silt would help erode the base plate please, and can I do anything about it legally?

What makes you think 2.5 mm has disappeared in such a short time? Did someone measure the exact parts of the base plate or is this two different people and their findings? Sounds like a big mistake somewhere to me?

[Matt&Jo]

That's a lot to eat through in such a short time...galvanic isolater fitted/working? Are you hooked up to marina electrics?

[Blue Angel]

I had her out last year for blacking and she was checked over then. 

She's out again now for another weld by the same person, so it is accurate

6 minutes ago, Matt&Jo said:

That's a lot to eat through in such a short time...galvanic isolater fitted/working? Are you hooked up to marina electrics?

All working, but yes have been in the Marina since Feb last year

[frangar]

I’d be asking how the measurements were done...and if the baseplate was blacked...unless you are moored in an acid bath that’s a lot to lose from “natural” causes in a year....is it over the whole width of the baseplate or is it just the chines if you have been sitting on the bottom...to give you some idea I’ve just had my chines plated on a  38 year old boat with a 6mm baseplate...and we are pretty deep draughted. 

[Tam & Di]

You'd have to be in a fairly strong acid to lose that much steel in just 12 months, and I can't believe it would be anything to do with the mud - even galvanic corrosion would not work that actively.

 

To look at it in practical terms, the Dutch say 4mm is acceptable plate thickness for a pleasure barge, but a hull that thick would have complete disappeared in under 2 years at the rate you mention. What does the surveyor who took the measurements say about it?

 

Tam

[Tam & Di]

Another point is you mention the guy doing the welding as being the person who did the sonic survey. Is he actually an accredited surveyor? It is quite easy to get false readings unless you are really experienced, and even then most surveyors would back them up with a hammer test.

 

Tam

[Alan de Enfield]

Didn't @WotEver or @Keeping Uplose more than that in a year - just on one side of the boat ?

 

Or was it someone else ?

Edited April 30, 2020 by Alan de Enfield

[Blue Angel]

22 minutes ago, Matt&Jo said:

That's a lot to eat through in such a short time...galvanic isolater fitted/working? Are you hooked up to marina electrics?

All working, but yes have been in the Marina since Feb last year

 

40 minutes ago, mrsmelly said:

What makes you think 2.5 mm has disappeared in such a short time? Did someone measure the exact parts of the base plate or is this two different people and their findings? Sounds like a big mistake somewhere to me?

 

4 minutes ago, Tam & Di said:

You'd have to be in a fairly strong acid to lose that much steel in just 12 months, and I can't believe it would be anything to do with the mud - even galvanic corrosion would not work that actively.

 

To look at it in practical terms, the Dutch say 4mm is acceptable plate thickness for a pleasure barge, but a hull that thick would have complete disappeared in under 2 years at the rate you mention. What does the surveyor who took the measurements say about it?

 

Tam

Thanks guys... it's been "pinged" with an electronic doofer (sorry, technical term evades me). My engineer said he thought it was due to the silt, but like you say, I was stunned at how much she has lost! I daren't go back to my old mooring now because at that rate I'm going to wake up one morning with no boat round me.

The main loss is down the centre if that helps?

4 minutes ago, Tam & Di said:

Another point is you mention the guy doing the welding as being the person who did the sonic survey. Is he actually an accredited surveyor? It is quite easy to get false readings unless you are really experienced, and even then most surveyors would back them up with a hammer test.

 

Tam

Yes Tam... he does welding, engineering and surveys. I do trust him as he has an excellent reputation in Cheshire

[Murflynn]

50 minutes ago, Blue Angel said:

I have just found that my base plate has deteriorated by 2.5mm over 12 months. I have the right number of anodes, but the Marina where I'm based is stilted up to the max. Does anyone know if silt would help erode the base plate please, and can I do anything about it legally?

you make it sound as if the whole of the base plate has lost 2.5mm. .................  very very unlikely.   if that really is the case it suggests that the meter being used needs re-calibrating.

 

the whole of the baseplate cannot be checked - only a number of points.

did your welder notice some corrosion and just measure at those points?

was the corrosion present at the same locations last time, and did he check the same locations?

 

as others have said, any meaningful survey procedure should be done in a very controlled and well documented manner.    my guess is that a welder doing thickness checks would not follow such procedures.

[Alan de Enfield]

4 minutes ago, Blue Angel said:

All working, but yes have been in the Marina since Feb last year

 

As I noted above, someone else on the forum had a very similar experience and was fully fitted out with GI and anodes - If I remember correctly it was traced to a neighbouring boat leaking 'electrical worms'.

 

Hope fully whoever it was will see the thread and comment.

[Blue Angel]

Just now, Murflynn said:

you make it sound as if the whole of the base plate has lost 2.5mm. .................  very very unlikely.   if that really is the case it suggests that the meter being used needs re-calibrating.

 

the whole of the baseplate cannot be checked - only a number of points.

did your welder notice some corrosion and just measure at those points?

was the corrosion present at the same locations last time, and did he check the same locations?

 

as others have said, any meaningful survey procedure should be done in a very controlled and well documented manner.    my guess is that a welder doing thickness checks would not follow such procedures.

No, just the centre line. 

When she was out last year he checked along the centre as there were signs of pitting then... I blacked her myself after treating with vactan, so Im pretty sure I did a good job.

2 minutes ago, Alan de Enfield said:

 

As I noted above, someone else on the forum had a very similar experience and was fully fitted out with GI and anodes - If I remember correctly it was traced to a neighbouring boat leaking 'electrical worms'.

 

Hope fully whoever it was will see the thread and comment.

Ok thanks for that... fingers crossed as I'm getting a bit stressed at the moment :o/

[Keeping Up]

25 minutes ago, Alan de Enfield said:

Didn't @WotEver or @Keeping Uplose more than that in a year - just on one side of the boat ?

 

Or was it someone else ?

Yes we lost more than that but in 18 months; we lost nearly 5mm from each side of the boat uniformly from bow to stern, waterline to base. The base plate was relatively unaffected, but as it was 12mm to start with it wouldn't have mattered a great deal if we had lost some metal there. We never found the cause of the problem.

[Mike Tee]

It was 'Keeping Up', although I'm not sure he ever identified where his hull problem came from.

One of my old boats was moored long term (before I got it) in a marina that was originally dug out for peat. That apparently created heavy pitting on the base plate, but removing it from the marina and frequent and liberal coats of blacking stopped any further damage.

 

eta - Allan is far quicker at typing than wot I am!! 

and it may have been puddling clay rather than peat, as dredging my memory suggests it was at Whixall marina but not 100% sure

Edited April 30, 2020 by Mike Tee

[Cheese]

Peat is more likely to be acidic than clay.

 

 

[WotEver]

1 hour ago, Alan de Enfield said:

Didn't @WotEver or @Keeping Uplose more than that in a year - just on one side of the boat ?

 

Or was it someone else ?

'Twas Mr UpKeeper iirc.

[Alan de Enfield]

1 hour ago, Mike Tee said:

It was 'Keeping Up', although I'm not sure he ever identified where his hull problem came from.

One of my old boats was moored long term (before I got it) in a marina that was originally dug out for peat. That apparently created heavy pitting on the base plate, but removing it from the marina and frequent and liberal coats of blacking stopped any further damage.

 

eta - Allan is far quicker at typing than wot I am!! 

and it may have been puddling clay rather than peat, as dredging my memory suggests it was at Whixall marina but not 100% sure

We moored for years in Whixhall, and was in fact going to buy the marina but BW (BWML) outbid us.

 

I was never aware of any particular corrosion problems, we were there late 1990's / early 2000's. We had a 45 foot 'Millenium ' 1999 boat.

[Bee]

When you say most of the loss is down the centre line of the boat is it 'V' bottomed? Springer maybe? Perhaps water has collected in the bottom of the boat and corroded it from the inside? Can't see how silt would have made much difference to the outside, coarse sand might have removed a couple of thou' over a long time but doesn't seem very likely.

[ditchcrawler]

44 minutes ago, Bee said:

When you say most of the loss is down the centre line of the boat is it 'V' bottomed? Springer maybe? Perhaps water has collected in the bottom of the boat and corroded it from the inside? Can't see how silt would have made much difference to the outside, coarse sand might have removed a couple of thou' over a long time but doesn't seem very likely.

I was wondering if water inside is giving a false reading

[Ianws]

3 hours ago, Mike Tee said:

It was 'Keeping Up', although I'm not sure he ever identified where his hull problem came from.

One of my old boats was moored long term (before I got it) in a marina that was originally dug out for peat. That apparently created heavy pitting on the base plate, but removing it from the marina and frequent and liberal coats of blacking stopped any further damage.

 

eta - Allan is far quicker at typing than wot I am!! 

and it may have been puddling clay rather than peat, as dredging my memory suggests it was at Whixall marina but not 100% sure

If it was puddling clay that caused it, shouldn’t we all get our boats off the cut sharpish!

[WotEver]

23 minutes ago, ditchcrawler said:

I was wondering if water inside is giving a false reading

Good thought.

[Mike Tee]

1 hour ago, Ianws said:

If it was puddling clay that caused it, shouldn’t we all get our boats off the cut sharpish!

Only going on what I was told by the people there at the time (1990's) - there was a suggestion that the base plate was virtually in contact with the canal bottom for quite a while - I'm not a metallurgist or boat surveyor so it's anybody's guess what caused quite severe pitting over just a few years (up to 4mm pits in a 12mm base) actually its probably the same steel supplier as Keeping Up's boat as they were built at the same yard at the same time!!

[David Mack]

If you have a localised loss of 2.5mm you should be able to see it, without needing ultrasonic measurements. So is the loss of metal from the outside or inside of the hull? If its on the inside then bilge conditions will be responsible, not the silt outside.

[Blue Angel]

Thank you everyone for your thoughts... 

My boat has had to have a full 8mm overplate on the base plate and the stern had to be completely rebuilt! Nothing to do with the silt it seems, just crap steel initially, and then many years of neglect before my time.

I now have a non-sinking, happy boat!! And a happy boater too!

Thanks again ?

[cuthound]

1 hour ago, Blue Angel said:

Thank you everyone for your thoughts... 

My boat has had to have a full 8mm overplate on the base plate and the stern had to be completely rebuilt! Nothing to do with the silt it seems, just crap steel initially, and then many years of neglect before my time.

I now have a non-sinking, happy boat!! And a happy boater too!

Thanks again ?

 

Thanks for getting back to us with an update, not everyone does.

 

Glad you got it sorted, it should last many years now.