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Kedian Engineering Overplating [pics]

Mitchellmoxo

By Mitchellmoxo
in Boat Building & Maintenance

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jenevers Rising Star

jenevers

Posted
Posted

That's a good question. You would think that if the gap between the plates is truly airtight, once all the oxygen in the trapped air had been used up the rusting process would stop. This is why there's a common belief that stationary boats in stationary water don't rust as fast as a moving boat where the supply of oxygen is constantly being replenished.

 

But it isn't that simple. As I understand it boats that are constantly on the move are more likely to rust evenly whereas boats that spend most of their life tied up are much more prone to pitting. I don't fully understand the science behind this but I think it is fact. So I'm tempted to think that the same might apply to an overplated boat where the air inside provides a limited supply of oxygen but it might well be enough to work on a small area, form a pit and eventually perforate the plating.

 

As a matter of interest I've just recovered a couple of 3mm mild steel offcuts which have been buried at the back of the garage for several years. Parts of the surface are unblemished but other parts have quite deep sections of localised rust. It's hardly a scientific analysis but this does tend to support the above theory.

Interesting. If only someone would come forward with actual proof of rusting taking place between plates, rather than the (understandable) theory that wet steel must rust.

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Neil2 Veteran

Neil2

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The problem is there's no way to force an experiment to see what actually happens. Those offcuts I retrieved from the garage had been sat there for maybe seven years and though the rust had taken hold in places, it was a long way from causing a perforation and that's only 3mm steel.

 

What we need is someone with an overplated boat that was done 10-15 years ago willing to have some of the plating removed for examination...

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jenevers Rising Star

jenevers

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The problem is there's no way to force an experiment to see what actually happens. Those offcuts I retrieved from the garage had been sat there for maybe seven years and though the rust had taken hold in places, it was a long way from causing a perforation and that's only 3mm steel.

 

What we need is someone with an overplated boat that was done 10-15 years ago willing to have some of the plating removed for examination...

Strange that no overplated boat has ever been shown to have any "in between plates" rusting failure. I'm sure that the towpath telegraph would have swiftly spread the story throughout the canal network. So..... is it a myth?

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cuthound Veteran II

cuthoundDonate to Canal World

Posted
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Strange that no overplated boat has ever been shown to have any "in between plates" rusting failure. I'm sure that the towpath telegraph would have swiftly spread the story throughout the canal network. So..... is it a myth?

I guess we will have to wait until the overplating wears or corrodes enough to need doing again.

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Martin Kedian Proficient

Martin Kedian

Posted
Posted (edited)

There are boats still on the cut after being over player 20 years before the boats built in the 70'soften only had 6mm base and sides I believe in the welding process the best involved uses up the air behind the overplateing steel.i have stretched an over plated boat and have had to remove some of the new steel and found little evidence of further rusting

I believe that over plating is a cost effective way of increasing the life of a boat that is uninsurable due to failing its test

Sorry should read plated and heat

Edited by Martin Kedian
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Neil2 Veteran

Neil2

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There was a strange case on here some time ago where someone had an overplated boat that had "failed" an insurance survey because the plating was too thin, according to the surveyor. I can't remember whether it was actual thinning of the plate or whether the plating was too thin to begin with, in the surveyor's opinion.

 

Just out of interest, could you paint or even zinc spray the back side of the plates prior to being welded up? Obviously the edges being welded have to be clean, but would the heat transfer cause problems?

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John V Veteran

John V

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When we were doing the main hull repairs on Sabina there was one doubling plate that was "popping off" due to the pressure of the rust behind. It was very amateurishly done (I could have done better and my welding is wiggly pigeon shit) The weld was breaking off along one side of the patch (almost no penetration) and the thin plate on the inside was bulging upwards. I suspect that water had been getting in to the space between from the inside over the years she had been a derelict. I didn't pay too much attention to it at the time as the whole of that section of the hull was being replaced.

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MtB Veteran II

MtBDonate to Canal World

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Always encouraging to get good feedback from surveyors

 

 

Not necessarily.

 

I had an A1 survey report on REGINALD three years ago, don't forget.

 

The guy spent AGES tapping the hull with his white stick so I knew it was gonna be good survey.

 

:)

 

MtB

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MtB Veteran II

MtBDonate to Canal World

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Your right I guess but for me it was music to my ears sorry for your experience

 

I can imagine it must have been after such a major amount of work done with such care.

 

My good survey three years ago was actually quite a surprise to me despite my flippancy above and I never really believed it, so the bad verdict this time around came as no surprise.

 

 

MtB

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BD3Bill Community Regular

BD3Bill

Posted
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Ahhh! Crystal!

 

Still on the bright side the little fella was already ashore & you didn't pay another £400 odd for a survey !

 

So much respect for you keeping an old boat going. Nice.

 

P.S. Having mastered the starting of the mighty Kelvin on Aldebaran I do hope I get the chance to spin up the Scania (sic) !

 

Cheers!

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cuthound Veteran II

cuthoundDonate to Canal World

Posted
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Not necessarily.

 

I had an A1 survey report on REGINALD three years ago, don't forget.

 

The guy spent AGES tapping the hull with his white stick so I knew it was gonna be good survey.

 

:)

 

MtB

But did you ask for a lab report from his guide dog? :)

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