New boat steel question

[WotEver]

1 hour ago, Mike the Boilerman said:

people expect boats to last forever so demand ever ticker steelwork. 

To be sure, to be sure...

[jonesthenuke]

3 hours ago, Mike the Boilerman said:

 

That's all a load of old bobbins in my view  ... boat builders don't go as far as calculating stuff like torsional rigidity!

 

The reason for the thicker steel nowadays is 40 years ago the industry was new and young and I reckon they just used the same thicknesses of steel as the riveted iron boats used iron. Boats were built to last 30 years back then but now people expect boats to last forever so demand ever ticker steelwork. 

 

And the rusting quicker thing, I've been hearing that said about steel of 30 years previously, ever since I was a teenager. 

I agree, I rather suspect its a story that has endlessly re-told since the change from using wrought iron to mild steel. That would have made a significant difference.

[Bee]

If you want to see old boats go to Holland, Lots of metal boats there that were built in the late 19th century , can't promise that they are very original underwater and overplating is very common but they are generally thinner steel than we use over here. Thing is though that they tend to be regularly hauled out and painted, we are just starting to realise that. Careful though, there are lots of old rust buckets as well.

[Captain Pegg]

On 4 April 2019 at 09:51, Mad Harold said:

My boat is a 30 footer built 1978,and still going strong.  Original steel thickness,6,5,3mm.

The last survey recorded less than 1mm steel loss all round,but with some pitting noted.

I think more modern larger boats are built with thicker steel because a longer boat will need more torsional stiffness,and also I think (but have no evidence of this) that modern steel is of poorer quality and rusts quicker than the old stuff. It's just my theory,and have mentioned this before on this forum,but people more knowledgeable than me,have said this is not true,and it's environmental factors that cause more rapid corrosion.

I am simply basing my theory on my own observations.  (Great is the mystery of faith)

 

I suspect I am the chief protagonist in disagreeing with you. Can you explain your theory; why would poorer quality steel be more prone to rusting?

 

JP

[Boater Sam]

Old steel boats were riveted Wrought Iron and basically it rusts so slowly so as to be negligible.

Mild Bessemer Steel is nothing like, it rust like crazy even in the open air.

Modern steel is made from recycled crap, is made fast and cheap.

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[Alan de Enfield]

6 minutes ago, Captain Pegg said:

I suspect I am the chief protagonist in disagreeing with you. Can you explain your theory; why would poorer quality steel be more prone to rusting?

 

JP

Whilst not asked for - my theory is that

1) water quality has changed over the last 20/30/50 years (cleaner water with higher oxygen levels).

2) there are many more electrical worms escaping from boats (particularly in marinas) these days than there were 20/30/50 years ago.

3) the make-up and effectiveness of the 'protective paints' (blacking) we use has been weakened due to legislation reducing 'nasties'.

[Captain Pegg]

1 minute ago, Alan de Enfield said:

Whilst not asked for - my theory is that

1) water quality has changed over the last 20/30/50 years (cleaner water with higher oxygen levels).

2) there are many more electrical worms escaping from boats (particularly in marinas) these days than there were 20/30/50 years ago.

3) the make-up and effectiveness of the 'protective paints' (blacking) we use has been weakened due to legislation reducing 'nasties'.

Don't necessarily disagree Alan, although we'll never know unless someone does a proper controlled test. I have said before that the chemicals put into marinas via cleaning products could be a factor as well. However none of that would be influenced by the steel itself and therefore isn't an answer to the question I posed.

 

JP

[Detling]

Being as the base plate is supposed to rust slower than the side (particularly at the waterline) the main reason for having a thicker baseplate is to reduce the amount of internal ballast required for a given headroom. If it had a 10mm baseplate it would float lower in the water maybe too deep, it all depends on the hull shape/design.

[Bee]

59 minutes ago, Alan de Enfield said:

Whilst not asked for - my theory is that

1) water quality has changed over the last 20/30/50 years (cleaner water with higher oxygen levels).

2) there are many more electrical worms escaping from boats (particularly in marinas) these days than there were 20/30/50 years ago.

3) the make-up and effectiveness of the 'protective paints' (blacking) we use has been weakened due to legislation reducing 'nasties'.

There could well be something in that, especially the electrical wriggly things. As for blacking, you could be right, especially on older boats that have always used bitumen. I reckon that modern paints are way better than bitumen but so long as the steel has something on it, it is protected. Modern cars don't rust like old cars so I doubt that the steel these days is any worse, its really all down to the boat being hauled out, pressure washed and painted every 2 or 3 years, I don't think there is any substitute for that even though it is a damned nuisance and can be expensive.

[MtB]

1 hour ago, Detling said:

Being as the base plate is supposed to rust slower than the side (particularly at the waterline) the main reason for having a thicker baseplate is to reduce the amount of internal ballast required for a given headroom. If it had a 10mm baseplate it would float lower in the water maybe too deep, it all depends on the hull shape/design.

 

 

I think thicker base plates are because base plates are so difficult to paint, so we don't paint them, we just let them rust. We have them thicker so the rust takes longer to eat through. 

 

But then the surveyors point out a 25 year old 10mm base plate is down to 6mm and the owners get panicked into welding another 8mm of steel over the top. Ridiculous, but that is wealthy middle class boat owners who know nothing about engineering, for ya. 

 

 

 

Edited April 6, 2019 by Mike the Boilerman
Speeling.

[Keeping Up]

2 hours ago, Detling said:

Being as the base plate is supposed to rust slower than the side (particularly at the waterline) the main reason for having a thicker baseplate is to reduce the amount of internal ballast required for a given headroom. If it had a 10mm baseplate it would float lower in the water maybe too deep, it all depends on the hull shape/design.

When our boat was built in 1991 the standard baseplate from our builder was 8mm but for additional cost you could have 10mm. Then I asked what about 12mm and he did the calculations: there would be no need for any ballast so the floor could be lowered to sit directly on the hull's cross-members, this meant there would be no need for separate floor bearers,  this actually meant it was cheaper overall to use 12mm than 10mm. As a result, despite a low roof-line which easily fits through Froghall, Standedge etc, internally we have more headroom than most other boats.

[Captain Pegg]

3 hours ago, Boater Sam said:

Old steel boats were riveted Wrought Iron and basically it rusts so slowly so as to be negligible.

Mild Bessemer Steel is nothing like, it rust like crazy even in the open air.

Modern steel is made from recycled crap, is made fast and cheap.

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That’s just plain wrong. The Bessemer process for steelmaking is long, long gone. Chemically the product was quite close to wrought iron with a low carbon content and therefore had good corrosion resistance. Modern steel isn’t mostly recycled but no matter the process used, it always starts with an impure product be it pig iron from the blast furnace or the intial melt in the electric arc furnace. It’s what happens after that which matters. In any case blast furnaces have always been charged with scrap. Modern steelmaking processes are actually slower than Bessemer but more controlled.

 

JP

Edited April 6, 2019 by Captain Pegg

[Chris Williams]

Just wondering - are we talking about British steel or Chinese?  Is the quality any different?  I have no idea.

[Boater Sam]

All those piles of rusted scrap that we export must finish up somewhere....................................

[Sea Dog]

46 minutes ago, Boater Sam said:

All those piles of rusted scrap that we export must finish up somewhere....................................

Yes, it must - otherwise there'd still be Vauxhall Vivas all over the place.

[Chris Williams]

1 hour ago, Boater Sam said:

All those piles of rusted scrap that we export must finish up somewhere.

Yes, back yur as Honda Accords.

[cuthound]

3 hours ago, Boater Sam said:

All those piles of rusted scrap that we export must finish up somewhere....................................

 

Not as many as the Italians must have exported though! ?

[Mad Harold]

10 hours ago, Captain Pegg said:

I suspect I am the chief protagonist in disagreeing with you. Can you explain your theory; why would poorer quality steel be more prone to rusting?

 

JP

I will try.    Narrowboat hulls don't corrode evenly all over,they start with pitting of the surface.If there are only a few pits,they can be spot welded,but if deep pits have spread over a large area then overplating or cutting out the corroded area and welding in new steel will be required.

Now,why do these pits start in the first place? why doesn't the steel corrode evenly?

My theory.  When steel is made iron ore,limestone and other ingredients that I don't know about are all melted together,and air is blasted through to get rid of the unwanted stuff (slag) and if this process is not done properly and slag is left in the steel to save a few quid,then that I think is where the rust pits will start.

It is just a theory,and am quite prepared for incoming because I don't have any qualifications in metallurgy,but I have seen steel being cut up with a torch for scrap.(my first wife's father had an industrial scrap business) and some steel cut like butter,and other stuff,there was sparks flying all over the place and was difficult to cut.

 

[Chris Williams]

I suspect the term 'steel' is much the same as 'plastic' - there are different grades and mixes.  I seem to remember something about 'EN' numbers.  The hull of 'Jaguar' allegedly had copper mixed in and never rusted, but other bits did.

[Captain Pegg]

13 hours ago, Mad Harold said:

I will try.    Narrowboat hulls don't corrode evenly all over,they start with pitting of the surface.If there are only a few pits,they can be spot welded,but if deep pits have spread over a large area then overplating or cutting out the corroded area and welding in new steel will be required.

Now,why do these pits start in the first place? why doesn't the steel corrode evenly?

My theory.  When steel is made iron ore,limestone and other ingredients that I don't know about are all melted together,and air is blasted through to get rid of the unwanted stuff (slag) and if this process is not done properly and slag is left in the steel to save a few quid,then that I think is where the rust pits will start.

It is just a theory,and am quite prepared for incoming because I don't have any qualifications in metallurgy,but I have seen steel being cut up with a torch for scrap.(my first wife's father had an industrial scrap business) and some steel cut like butter,and other stuff,there was sparks flying all over the place and was difficult to cut.

 

Fair play, at least it's a logical theory not just an idea.

 

Slag is lighter than iron or steel so when iron is produced in the blast furnace, or steel in the converter, the slag floats on top and the metal is tapped from underneath. To mix slag in with the metal would take a lot of effort. It would also produce a material that would be blatantly unfit for purpose long before it ever got as far as corroding some years down the line. Slag doesn't rust anyway.

 

Steel is possibly the most researched and developed material in history and while other folks are developing the technologies for taller buildings, longer bridges, bigger ships and faster railways the narrowboat world is pondering whether a lump of the stuff is fit to float in a ditch while using less than 1% of it's mechanical strength. One of the reasons the engineering wonders of the modern world can be built is the continual development and improvement of steel technology.

 

Pitting is a symptom of something other than pure ambient corrosion e.g. something chemically or electrically induced.

 

JP

[Captain Pegg]

20 hours ago, Chris Williams said:

Just wondering - are we talking about British steel or Chinese?  Is the quality any different?  I have no idea.

 

13 hours ago, Chris Williams said:

I suspect the term 'steel' is much the same as 'plastic' - there are different grades and mixes.  I seem to remember something about 'EN' numbers.  The hull of 'Jaguar' allegedly had copper mixed in and never rusted, but other bits did.

The number of boats on UK inland waterways made from Chinese steel probably tends toward zero currently. Yes there are many grades of steel but boats are pretty much universally made from ordinary mild steel. Corrosion resistance is a function of the particular alloy and not of the "quality" of production per se.

 

Copper bearing steels are malleable and have good corrosion resistance hence are good for boats with curves and those used in estuarine environments. It is of course expensive.

 

Steel production is generally of an equivalent standard around the world. I tested this theory with a metallurgist colleague of mine who has worked in the assurance field of steel production as a consultant. He suggested some Chinese products are probably better than their UK equivalents. They trade know how for strict procedural control. Nonetheless both will meet the specified range of properties required for the same application.

 

20 years ago the same comments now levelled at Chinese steel were aimed at Italian steel. Ironically steel from Eastern Europe has probably seen the biggest increase in it's share of the UK market in that time. However that has gone unnoticed as we seem to fear China more than Poland.

 

Leaving the free trade area that supplies 40% of our steel seems to be a certain way of ensuring the market share of Russian, Chinese and Indian steel increases so let's hope I am correct about standards.

 

JP

Edited April 7, 2019 by Captain Pegg

[Chris Williams]

3 hours ago, Captain Pegg said:

the narrowboat world is pondering whether a lump of the stuff is fit to float in a ditch while using less than 1% of it's mechanical strength.

The problem is that half the time, it is not floating, it is scraping along the bottom of the ditch.

[Alan de Enfield]

5 minutes ago, Chris Williams said:

The problem is that half the time, it is not floating, it is scraping along the bottom of the ditch.

And, the other half its tied up.

[Chris Williams]

6 hours ago, Alan de Enfield said:

And, the other half its tied up.

At least half.   but we have been there before.

 

[The dog lady]

Have been looking at a boat builder who says they shot-blast new hulls before epoxy blacking to remove 'mill scale' -  a type of iron oxide which is formed during hot rolling process - which would otherwise eventually flake off taking top coatings with it and allowing pitting and corrosion. Is this common practice?