Jump to content

NB lifespan?


Jason G

Featured Posts

3 hours ago, john.k said:

I wondered about corten ....its been stated on this forum by experts that the metallic impurities in steel cause pitting corrosion......if so ,then 10% or so of copper may /maynot be a good idea................

Several of the Joshers were built of "coppered steel", but I don't know what the actual composition was.

Edited by David Mack
Link to comment
Share on other sites

Compared to some our boat is still fairly young ( built 1999) but the engine, a Lister HRW2 had a previous life as the engine in a RN workboat. Thankfully they converted it to electric start, but kept the hand crank available, just in case. As with all working engines if you look after them they will carry on for years.

Link to comment
Share on other sites

18 hours ago, Dav and Pen said:

It was never the practice to black the underside of the working boats and we never even thought about it. We did try and keep the inside of the bottom red oxided as thought the rainwater would cause corrosion from the inside. The original bottom plates of the Town class were of 3/8th inch shipbuilding steel and in the case of Tadworth lasted nearly 40 years since then she has had 3 new bottoms so something has changed.

Our Dutch barge was built in 1917 and it was claimed that steel produced before 1920 was of higher quality before all the scrap steel from the First World War was available. The hull was 5.5mm steel and a lot of it was still above 4mm in 2001 but it had some overplating on the bilges and pitting on the waterline having been unused for some years in the brackish waters of Amsterdam harbour.  It is certainly the general practice to black the bottom of all the barges on the continent and they were always high enough when in dock for someone to get underneath. This was one job I was pleased to pay somebody to do.

 

To put that into context there was no iron industry in the Netherlands until the 1920s and steel was first produced at Hoogovens, IJmiuiden, in the 1930s. Everything before that would have been imported.

 

Since the issue of scrap in steel production was the starting point for the resurrection of this thread let's put it into proper perspective.

 

At a simplistic level the manufacture of steel is a two stage process. The first stage is ironmaking to create a pool of molten iron, and the second phase is steelmaking in which the molten iron is refined into an iron alloy with a specific chemical composition.

 

There are two ways of producing the pool of molten iron. One being to smelt rocks (iron ore, coke and limestone) in a blast furnace, and the other being to melt ferrous scrap in an electric arc furnace.

 

A blast furnace produces pig iron which is a particularly crude and dirty product containing more than 10 times the amount of carbon than common steel alloys require. It also contains significant amounts of silicon and sulphur, the latter being a particular nuisance in steel production. By contrast the base material for melted scrap will consist mostly of mild steel and the starting point for the steelmaking phase of the operation will be a lot closer to the finished product than if using pig iron.

 

Irrespective of the method of creating the pool of molten iron the steelmaking process in both cases involves analysis of the molten material and manipulating it by removal of unwanted elements by oxidisation and retaining specified amounts of those elements alongside, and in combination with, added alloying elements.

 

In summary then the bit that matters isn't how you source the iron but in how you process it.

 

 

Link to comment
Share on other sites

I know from when the refinery tanks were resheeted ,some plates were good enough to reuse,while every here and there was a plate completely pitted thru (and the cause of the resheet.)...refinery tanks have a floating lid on the  product to limit vapour space ,and a roof proper ,the dome you see in pictures.....there is always rainwater leakage in the space,and probably 100% humidity a lot of the time.

Link to comment
Share on other sites

47 minutes ago, Captain Pegg said:

 

To put that into context there was no iron industry in the Netherlands until the 1920s and steel was first produced at Hoogovens, IJmiuiden, in the 1930s. Everything before that would have been imported.

 

Since the issue of scrap in steel production was the starting point for the resurrection of this thread let's put it into proper perspective.

 

At a simplistic level the manufacture of steel is a two stage process. The first stage is ironmaking to create a pool of molten iron, and the second phase is steelmaking in which the molten iron is refined into an iron alloy with a specific chemical composition.

 

There are two ways of producing the pool of molten iron. One being to smelt rocks (iron ore, coke and limestone) in a blast furnace, and the other being to melt ferrous scrap in an electric arc furnace.

 

A blast furnace produces pig iron which is a particularly crude and dirty product containing more than 10 times the amount of carbon than common steel alloys require. It also contains significant amounts of silicon and sulphur, the latter being a particular nuisance in steel production. By contrast the base material for melted scrap will consist mostly of mild steel and the starting point for the steelmaking phase of the operation will be a lot closer to the finished product than if using pig iron.

 

Irrespective of the method of creating the pool of molten iron the steelmaking process in both cases involves analysis of the molten material and manipulating it by removal of unwanted elements by oxidisation and retaining specified amounts of those elements alongside, and in combination with, added alloying elements.

 

In summary then the bit that matters isn't how you source the iron but in how you process it.

 

 

They were do that last night on "How do they do that" making stainless steel, mixing scrap with pig iron, removing the carbon and then pouring and rolling  

Link to comment
Share on other sites

12 minutes ago, ditchcrawler said:

They were do that last night on "How do they do that" making stainless steel, mixing scrap with pig iron, removing the carbon and then pouring and rolling  

 

I wasn't watching so I didn't base my post on that!

 

Stainless has a very high percentage of added chromium and nickel (which constitute about a quarter of the finished alloy) and would be considered as a 'high quality' product by metallurgists and engineers. That is because of it's superior properties compared to the much more common carbon steel group. In engineering the use of the term 'quality' is used in reference to the specification against which the steel in question is produced and has nothing to do with whether any specific piece had been correctly manufactured in accordance with that specification and is otherwise free of manufacturing defects. I tend to put the word in inverted commas in my posts because I don't think the boating community use the term in the same way as engineers and metallurgists.

  • Greenie 1
Link to comment
Share on other sites

On 13/12/2021 at 10:36, ditchcrawler said:

Isnt that where the Concoform name came from at Weedon

 

No, I hired from them in the 80's and remember their brochure saying that Norman Clarke (the proprietor) had previously owned a concrete pumping business called Concoform, where he pumped concrete into shuttering or moulds.

 

It also had some photos of the family digging out the basin oin the grounds of the former Weeden Bec station, which had been closed by Beeching.

Link to comment
Share on other sites

On 12/12/2021 at 22:34, dmr said:

 

I think most boat yards would agree with you, most boats rust slowly but there are a few that pit quite quickly which is likely to be due to poor steel.

 

The timbers that boats sit on in the drydock are called bostocks, but its currently normal not the black or epoxy the baseplate. "Officially" this is because there is less oxygen down there and rusting is slower. More likely its because it is just too difficult/unpleasant to do in most dry docks.  The boat builders are well on top of this, whist boat sides are in 6mm steel the baseplate is 10mm (or even 12) so it still gets a reasonable life even unprotected.

The supports in a dry dock are stocks, Bostocks are a graduated line of stocks, for boats that are not flat or even keeled.

Link to comment
Share on other sites

36 minutes ago, Tracy D'arth said:

The supports in a dry dock are stocks, Bostocks are a graduated line of stocks, for boats that are not flat or even keeled.

 

That's interesting, most drydock operators call their supports bostocks. There appears to be a few words on the cut, like gunnels, where the meaning or name has possibly changed over time.

 

 

Link to comment
Share on other sites

1 hour ago, cuthound said:

 

No, I hired from them in the 80's and remember their brochure saying that Norman Clarke (the proprietor) had previously owned a concrete pumping business called Concoform, where he pumped concrete into shuttering or moulds.

 

It also had some photos of the family digging out the basin oin the grounds of the former Weeden Bec station, which had been closed by Beeching.

Ta, our first two years hire was from them as well, probably late 80s

Link to comment
Share on other sites

I am beginning to think the great advantage of steel as a boatbuilding material is that it is endlessly repairable but the great disadvantage is that it needs endless repairing. I think boats should be built of a wood/GRP/steel /rubber/ferrocement  sandwich painted with an epoxy/tar/creosote goo and that surely must cover every type of corrosion and rot known to boat owners.

Link to comment
Share on other sites

Create an account or sign in to comment

You need to be a member in order to leave a comment

Create an account

Sign up for a new account in our community. It's easy!

Register a new account

Sign in

Already have an account? Sign in here.

Sign In Now
  • Recently Browsing   0 members

    • No registered users viewing this page.
×
×
  • Create New...

Important Information

We have placed cookies on your device to help make this website better. You can adjust your cookie settings, otherwise we'll assume you're okay to continue.