Kedian Engineering Overplating [pics]

[Martin Kedian]

Hi Mike it wasn't a serious comment just my slightly warped sense of humor I think your contributions are very complementary two ways of dealing with the same problem I think often peoples opinion on overplateing versus replating is based on what they have heard rather than fact from some of the feedback on this thread I think it has helped this subject be less cloudy

Sorry if I have confused things I admire your commitment to the restoration you are doing I guess its horses for courses both overplateing and replating have a part to play

Cheers Martin

[bizzard]

I wouldn't keep it in the bread bin though. It could be mistaken for a piece of Ryvita.

[b0atman]

that looks to be a real boaters bread bin

[Tesla]

I wouldn't keep it in the bread bin though. It could be mistaken for a piece of Ryvita.

Doubt it, it will be much tastier than Ryvita...

[Neil2]

Doubt it, it will be much tastier than Ryvita...

Certainly more food value in it.

[Martin Kedian]

Good if you have a low iron count

[bizzard]

Certainly more food value in it.

Irons good for you, just beware of magnets.

[Neil2]

Apologies for hijacking your thread KEDIAN. I can ask a mod to split this into two separate threads if you wish.

 

But in the meantime I'll just say that much of the baseplate on Reg is still a good 6mm to 8mm thick and hardly seems to need changing. But there are areas where it is scarily thin. See this photo of a small section of baseplate about 3" x 9" that I now carry around with me, cut from near the fore end of the boat. I've included a £1 coin for scale. The whole section is about an average of 3mm thick and you can just see a foil-thin section to the left of the coin.

 

 

 

MtB

P.S. The interesting thing is how both sides of the sample look the same - equally rusty and pitted. Shows that corrosion was attacking the metal from both sides for a very long time.

But, - is my memory correct - we are looking at a piece of steel that is over 100 years old?

[Starcoaster]

Yes, the original bits of Reg's arse are pre-1900. Personally I was shocked at how thick a lot of it still is!

We also learned on Sunday that some of the rivets that were in perfectly good nick in 2011 when Reg was out last were also a hair's breadth away from failing too..

 

Slightly unrelated, but I have to say that the whole process has been soooo interesting to see, and Simon Wain is a really interesting bloke to talk you through stuff/explain stuff to you, neatly managing to explain everything clearly without talking down to you.

Standing upright in the inside is totally surreal, looking at the ceiling and fittings of the bedroom I've slept in hundreds of times, while standing on the open ground! A very odd sensation.

Edited January 27, 2015 by Starcoaster

[madcat]

Very interesting .

[Springer]

 

Apart from the very smallest Springers, it's rather more complex than that.

They generally have a narrow flat section in the centre, then the main part of the bottom is at a shallow angle to the horizontal, then the chine section is nearer vertical then horizontal, & finally the side is (nearly) vertical, so yes, a lot more work.

 

Tim

 

 

Having just completed overplating my 30ft springer from keel (the 150mm wide flat bit at the bottom) to gunwhales, every plate cut by hand and being a V had to turn her on her side to sucessfully weld the bottom, a lot more work but worth it.....

 

deluded not.....!

 

springer

[David Mack]

Apologies for hijacking your thread KEDIAN. I can ask a mod to split this into two separate threads if you wish.

 

But in the meantime I'll just say that much of the baseplate on Reg is still a good 6mm to 8mm thick and hardly seems to need changing. But there are areas where it is scarily thin. See this photo of a small section of baseplate about 3" x 9" that I now carry around with me, cut from near the fore end of the boat. I've included a £1 coin for scale. The whole section is about an average of 3mm thick and you can just see a foil-thin section to the left of the coin.

 

 

 

MtB

 

P.S. The interesting thing is how both sides of the sample look the same - equally rusty and pitted. Shows that corrosion was attacking the metal from both sides for a very long time.

That reminds me of this picture from the Badsey restoration page:

 

Edited January 28, 2015 by David Mack

[jenevers]

Overplating or replating?

 

The problem with overplating as many of us know, is that if any water gets between the plates (either from inside or outside), then it's impossible to get it out. Overplating creates potential water traps and corrosion points.

 

Having had a hull overplated 15 years ago when I was a bit green, these days I'd always want any thin steel cropped out and the area properly replated.

I've heard this argument before but, even if water does get trapped between the plates, oxygen is required as well as water, for rusting to take place. So would oxygen be present? I understand that instinctively, people would expect rusting to take place but has anyone any actual experience or hard evidence of this being the case? Or are we all just assuming this is what happens?

[Martin Kedian]

There are many over plates that have water between the plates the skill is to ensure it doesn't happen I take your previous point black rose about pin holes but a good welder always inspects his weld as he goes along bad welding can sink a new shell so the same diligence is required for both jobs In the case of the boat I am overplateing now it has holes in the boat below the waterline so ingress of water is definitely not recommended As you say both oxygen and water are needed for rust to occur boats on the sea bed remain in good un rusted condition for years There are so many desgns of boat as well which impacts on things the current boat is a wet bilge the water entering the front deck flowes under the floor to the rear of the boat and is bilge pumped overboard we are addressing this by plating in the bottom of the bulkheads

I would doubt that the space between the plates has no air so the answer is to stop any water getting behind the external plates

I hope this helps answer your question thanks for your post Martin

[jenevers]

There are many over plates that have water between the plates the skill is to ensure it doesn't happen I take your previous point black rose about pin holes but a good welder always inspects his weld as he goes along bad welding can sink a new shell so the same diligence is required for both jobs In the case of the boat I am overplateing now it has holes in the boat below the waterline so ingress of water is definitely not recommended As you say both oxygen and water are needed for rust to occur boats on the sea bed remain in good un rusted condition for years There are so many desgns of boat as well which impacts on things the current boat is a wet bilge the water entering the front deck flowes under the floor to the rear of the boat and is bilge pumped overboard we are addressing this by plating in the bottom of the bulkheads

I would doubt that the space between the plates has no air so the answer is to stop any water getting behind the external plates

I hope this helps answer your question thanks for your post Martin

Thanks for the info. If the pinprick was at the top of any welding I would think that all air would be forced out by the ingress of water. Also, I wonder if any "old air" ie. trapped for years, contains any oxygen.

[Neil2]

Thanks for the info. If the pinprick was at the top of any welding I would think that all air would be forced out by the ingress of water. Also, I wonder if any "old air" ie. trapped for years, contains any oxygen.

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.

[David Mack]

Standing upright in the inside is totally surreal, looking at the ceiling and fittings of the bedroom I've slept in hundreds of times, while standing on the open ground! A very odd sensation.

But is it as odd as the sensation that you get knowing you have slept in that bedroom hundreds of times, with only a sheet of ryvita keeping out the water below?

[Kwacker]

What about the elephant in the room? ..... how will you deal with replacing/reproducing the rivets ..... or not?

ps what an interesting thread this has been, thanks for all the photos.

Edited January 28, 2015 by Kwacker

[jenevers]

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.

[Neil2]

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...

[cuthound]

What sort of boat is Reginald?

A submarine.

[Starcoaster]

Har! He's a converted Stewarts and Lloyds day boat.

[tree monkey]

A submarine.

I do wonder about this considering how many times reg has been underwater

Edited January 28, 2015 by tree monkey

[jenevers]

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?

[cuthound]

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.