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Is overplating really that bad?


Dave_P
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13 minutes ago, roland elsdon said:

the myth of not painting the baseplate. 

WotEver's baseplate wasn't painted, so it's not a myth. 

10mm plate with a minimum thickness of 10mm when she was surveyed.

Mind you they had to pressure wash all the mussels off first. 

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7 hours ago, blackrose said:

That's probably because the epoxy paints available in the 1970s were a far cry from what is available these days. I've seen boats painted with epoxy coatings that were in perfect condition when the boat came out the water 10 years later. I'm not sure how you're defining panacea but personally I think two-pack paints if properly applied are a LOT better than the traditional alternatives. Of course the correct grade of steel should be specified for a new build, but that won't stop it corroding along the waterline so why not apply a properly specified coating too? Two pack epoxy paints are used in industry on commercial projects and I'm afraid the fact you're calling it "snake oil" shows that you don't really understand the subject.

Your comments here may give the wrong impression that coating technology has 'leaped forward considerably' in the last 50 years ie '....far cry......'. Whilst I will not agree or disagree on your view on 1970's epoxy vs today, what I can say is that todays epoxies are not a lot different to 1980's epoxies. The basic 2 pack epoxy systems of the 80's were fine coatings and as good as you will find today. The main advances over the past 30 years has been finding new 'molecules' to add to give a degree of surface tolerance ie hydrophilic components such as siloxanes but these come with negatives as they 'weaken' the epoxy matrix so usually will be more permable to water and oxygen (although that is usually good enough). The big problem however since the 80's is that regulations have changed and now VOC (volatile organic content) is key, as is the type of solvents used. Many of the typical solvents of the 70's and 80's can no longer be used so we have formulations that have big compromises to reduce VOC and replace the 'best' solvents. Give me a 2 pack epoxy from the 80s anyday - 'cause I know it will work. The basic epoxy chemistry (Bisphenol A/Epichlor hydrin) has not changed. Solvents have got worse. Additionally in the 70's you could sand blast. Now you can only grit blast. Big difference.

Life expectancy of coating has not changed between 1985 and now.

Not a lot different to the Red lead story. Best primer on the planet......now banned.

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21 minutes ago, BWM said:

I'm sure that steel quality varies from year to year, possibly due to market fluctuations in the price meaning different source countries/standards? 

No, for a couple of reasons.

First is that the biggest single source for the UK steel market is UK produced steel. After the UK comes the rest of the EU and overall the vast majority of the UK steel market is produced in the EU. Russia, India and China all import a small amount but one that is growing. One day it's conceivable that all UK steel will come from China and India but their share today is still a small minority.

The other reason is that steel is produced to an international standard and traded as an international commodity and does not significantly vary in standard.

Technical standards have changed in name and nomenclature from British to European to International but the basic composition and quality of the steel you can buy is pretty much the same as it has been for the past 40 years.

And if you buy it from a stockholder it's all 'British sourced'.

JP

 

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4 minutes ago, nb Innisfree said:

I thought grit blasting was the same as sand blasting, or did you mean shot blasting?  

Sand blasting uses sand ie silica sand. Bad for the health. You die if you breath in 1mg of dust at 1 mile away.

Grit blasting uses something different although I am not quite sure of the exact composition - viz grit!! Iron ore slag or something similar.  You dont die if you breath in the dust. Problem is that the grit is a bigger particle size and sand was better at getting a good surface and sand was much much cheaper. Getting a boat sandblasted was therefore much cheaper than grit blasting AND it was more likely to be done properly as it was easier to do......maybe that is a bit ott.

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1 hour ago, roland elsdon said:

More important may be the myth of not painting the baseplate. Yes in the old days boats wore out ( hence composite bottoms easier to replace in the 30s, now they rust out. If your boat floats on a puddle there is no reason not to paint the baseplate. Hence my surveyors comments there's some pitting on the baseplate-  best blasted and epoxy into the pits, to slow it down. Sadly pits from bottom turned out to be too near the waisting from the top, caused by.... Water in the hold.

Agree entirely. How on earth can you make a decision not  to paint a big sheet of steel that you then chuck in the water for the rest of its life. We all know what it will look like if we drag it out in a few years time, horrible and rusty.

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46 minutes ago, Captain Pegg said:

No, for a couple of reasons.

First is that the biggest single source for the UK steel market is UK produced steel. After the UK comes the rest of the EU and overall the vast majority of the UK steel market is produced in the EU. Russia, India and China all import a small amount but one that is growing. One day it's conceivable that all UK steel will come from China and India but their share today is still a small minority.

The other reason is that steel is produced to an international standard and traded as an international commodity and does not significantly vary in standard.

Technical standards have changed in name and nomenclature from British to European to International but the basic composition and quality of the steel you can buy is pretty much the same as it has been for the past 40 years.

And if you buy it from a stockholder it's all 'British sourced'.

JP

 

There may be other factors at work but I remember hearing about and seeing boats built in the mid 2000s that has more extensive corrosion than most from the 80s-90s, not scientific but notable. 

Have seen similar on domestic copper pipework, with some developing pin holes for no other reason than quality when installed.

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The 10mm base plate on our 35 year boat had a few minor pits in it, and none any more than 1mm deep, so the "myth" is proved in my opinion. Mind you our boat sat more than 30 inches below the water level, so maybe shallow draught contributes to base plate pittimg.

Edited by David Schweizer
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3 hours ago, David Schweizer said:

The 10mm base plate on our 35 year boat had a few minor pits in it, and none any more than 1mm deep, so the "myth" is proved in my opinion. Mind you our boat sat more than 30 inches below the water level, so maybe shallow draught contributes to base plate pittimg.

WotEver only had an 18" draft or thereabouts. No paint on the base plate, no corrosion either. Built in the 80's. It's no myth. 

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13 hours ago, BWM said:

I'm sure that steel quality varies from year to year, possibly due to market fluctuations in the price meaning different source countries/standards? 

No no no no, we have done this before. Steel or in fact any alloy of any metals is made to an exact recipe and and is tested rigorously to ensure it conforms to the correct standard. This applies to all metals irrespective of where they were produced 

Phil

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I was moored next to an immaculate Hudson ( other examples-are available) in 2005 on the ashby canal. The owner was telling me that his boat was in trouble, the 6 mm footings had failed survey on pitting. He was in a conundrum as to what to do. He was the second owner and while Steve Hudson was sympathetic he wasn't in a position to be in any way liable. Polish steel....

 

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24 minutes ago, roland elsdon said:

I was moored next to an immaculate Hudson ( other examples-are available) in 2005 on the ashby canal. The owner was telling me that his boat was in trouble, the 6 mm footings had failed survey on pitting. He was in a conundrum as to what to do. He was the second owner and while Steve Hudson was sympathetic he wasn't in a position to be in any way liable. Polish steel....

 

And only boats with Polish steel suffer pitting?

Is there a definitive way of knowing the source of steel on a modern new build? I thought in general that was something that wouldn't be known by a boat owner.

For every example where someone cites a particular problem with a particular type, origin or age of steel there are thousands of other examples of boats with the same properties that are fine. Not to mention the knowledge gained from the very much more demanding use of steel in other industries.

To me the key to ensuring the longevity of steel hulls lies in determining the cause of pitting. Steel plates of 6 to 10mm thinkness do not suffer general corrosion by oxidisation in either air or fresh water or a combination of both in any timescale that will bother a boat owner but the actions of chemical, biological and electrical corrosion are not fully understood.

Over the past 40 years consider what has changed;-

- the internal specification of boats to include significantly greater electrical power

- the introduction of AC

- shore supply

- the chemical composition of protective coatings 

- the pH of the water with changes to agricultural practice in relation to pesticides

The answer lies in there somewhere. Also consider that every boat has a pretty much unique set up and environment. It really isn't about the steel; that's the one consistent part of the equation.

JP

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2 hours ago, Phil Ambrose said:

No no no no, we have done this before. Steel or in fact any alloy of any metals is made to an exact recipe and and is tested rigorously to ensure it conforms to the correct standard. This applies to all metals irrespective of where they were produced 

Phil

I struggle with this, even steels in automotive use have different rates of corrosion- admittedly less of an issue today,  I have seen an alpha Romeo literally disappear whilst other marques have remained untouched. All would have started out with similar painted finishes, etc.

With more steels being recycled, surely the rate of potential impurities may increase? British, German and certain Japanese steels have long been held in high regard, there must be a reason for this. 

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18 minutes ago, BWM said:

I struggle with this, even steels in automotive use have different rates of corrosion- admittedly less of an issue today,  I have seen an alpha Romeo literally disappear whilst other marques have remained untouched. All would have started out with similar painted finishes, etc.

With more steels being recycled, surely the rate of potential impurities may increase? British, German and certain Japanese steels have long been held in high regard, there must be a reason for this. 

Remember the Lancia Beta,s from late 70s early 80s, most of them were scrapped at the first MOT at 3 years old. Italian steel at that time was rubbish.

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I recall Rover SD1s going rusty by the hundreds (my brother-in-law had one). It had nothing to do with the steel. It had everything to do with unpainted body shells rusting in a field prior to the car being built. Teams of guys with wire wool and oil never got them completely rust free nor completely clean. 

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6 minutes ago, BWM said:

Yes, I certainly do. I'm sure there was a stratos bought into the paintshop I worked in that even had a door mirror shell that resembled a doily. Don't mention 'datsun'!

I had a Datsun 180B in about 1988, you could lie in bed at night and hear the thing getting eaten by rust.

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6 minutes ago, WotEver said:

I recall Rover SD1s going rusty by the hundreds (my brother-in-law had one). It had nothing to do with the steel. It had everything to do with unpainted body shells rusting in a field prior to the car being built. Teams of guys with wire wool and oil never got them completely rust free nor completely clean. 

Might have been the case in those circumstances but more often the metal would fail on either a bend or seam, where the metal had been worked-potentially bringing impurities out.

A friend used to work in structural engineering and very often all concrete mixtures and steels were tested for conformity, there must have been a reason for that. 

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3 hours ago, BWM said:

I struggle with this, even steels in automotive use have different rates of corrosion- admittedly less of an issue today,  I have seen an alpha Romeo literally disappear whilst other marques have remained untouched. All would have started out with similar painted finishes, etc.

With more steels being recycled, surely the rate of potential impurities may increase? British, German and certain Japanese steels have long been held in high regard, there must be a reason for this. 

when the steel is smelted all the impurities form a skin on the surface known as slag. The steel is poured of leaving the slag behind

Phil

 

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9 minutes ago, Phil Ambrose said:

when the steel is smelted all the impurities form a skin on the surface known as slag. The steel is poured of leaving the slag behind

Phil

 

I understand that, but even when doing forge work you continue to form a skin of impurities as you heat, work and cool the work down. Some of this i'm sure is down to carbon content, but not all. 

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16 hours ago, WotEver said:

WotEver only had an 18" draft or thereabouts. No paint on the base plate, no corrosion either. Built in the 80's. It's no myth. 

 

1 hour ago, BWM said:

I understand that, but even when doing forge work you continue to form a skin of impurities as you heat, work and cool the work down. Some of this i'm sure is down to carbon content, but not all. 

All steel has a carbon content, that's what makes it different iron. The degree in terms of percentage of carbon content makes different grades of steel to be used for different purposes.

 Other materials are added to steel to make any one of hundreds of grades of steel, lead is added for instance to make a very free cutting steel, this steel known as Leadalloy lends itself to producing components very quickly where strength is not an issue.

when steel is hot worked yes a skin forms , we know that as mill scale, this does not detract from the quality of the steel.

I suggest if you are really interested then you do a bit of reading on the matter of materials and their qualities.

One of my favourite's is Beryillum Copper, about 2% of Beryillum is added to copper to make it a similar hardness to steel.

Phil 

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5 hours ago, Mike Hurley said:

Remember the Lancia Beta,s from late 70s early 80s, most of them were scrapped at the first MOT at 3 years old. Italian steel at that time was rubbish.

Or perhaps the steel specification, treatment, fabrication and protection was rubbish. Automotive steels are used in very thin sheets in a very aggressive environment so need to be well specified and built.

I find it hard to see that you could produce a naturally fast rusting steel even deliberately. At the end of the day it's a lump of purified iron. There is a limit to how quickly it can rust naturally. On the other hand if you use the wrong specification, pare down the quantity to the bare minimum, fabricate it badly and protect it badly for the environment it will work in then that's a different matter. So I suggest rather like narrowboats the steel gets the blame because that's where's the symptoms are visible; but it isn't the cause.

JP

 

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