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sunny

baseplate to black or not to black

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2 minutes ago, sunny said:

What are peoples views on baseplate blacking Should it be done or not

You'll probably get a 50/50 split of folk saying do it/don't bother.  I'm aware of 30+ year old boats boats with unpainted baseplates with virtually zero corrosion, and I've read of much younger boats with painted baseplates with lots of pits.  It's a filthy job, so that's one reason some folk don't bother.

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Depends where you get it done if it is a filthy job or not 🙂 The dry dock at Northwich is the cleanest and driest  dry dock I have ever seen and you can get the boat up high enough  so that you (or someone!) can slide underneath on a sort of laid back chair thing.to do the job. 

 

haggis

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2 minutes ago, haggis said:

>>you can get the boat up high enough  so that you (or someone!) can slide underneath on a sort of laid back chair thing.to do the job. <<

 

And then faff about with the supports to black the bits that you couldn't reach? And then faff about with the supports again to get the second coat on the bits that are now inaccessible? 

 

 

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2 minutes ago, Machpoint005 said:

 

And then faff about with the supports to black the bits that you couldn't reach? And then faff about with the supports again to get the second coat on the bits that are now inaccessible? 

 

 

This is the bit I've wondered about too when considering blacking the baseplate. No point doing any of it if you can't do all of it. In a dry dock this would mean refloating several times which they surely don't do.

  • Greenie 1

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3 minutes ago, Dave123 said:

No point doing any of it if you can't do all of it.

 

My point, succinctly put!

 

 

 

 

Edited by Machpoint005
'cos my 'puter can't spell

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It's not real world practical. It' s one of the reasons baseplate is thick. The coating will get penetrated anyway soon after blacking unless you never ground the boat.

 

Consider electrolytic corrosion. Is it better to have a uniform metal loss across the bottom plate or concentrated in one or two spots where the coating has failed possibly leading to localised pinholes?

 

Edited by mark99
  • Greenie 2

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3 minutes ago, mark99 said:

>>concentrated in one or two spots where the coating has failed possibly leading to localised pinholes<<

 

Excellent point.

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1 hour ago, sunny said:

What are peoples views on baseplate blacking Should it be done or not

No.

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I had it done when I first got the boat in 1992...boat was then 9 years old and baseplate was badly pitted. Done it ever since and no more pits...readings the same on the last survey as when I got it. Now had it grit blasted & molten zinc sprayed...even with a deep draught there’s little removed 

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Why on earth wouldn't you paint it? Lift a floorboard or two, no rust? that's because its dry. Lots of rust? that's because it is or has been wet. Wet steel will corrode - badly and sometimes very quickly. The only reasons not to paint it is if you don't care or you cannot get to it. Do people with sailing boats, round bilge or vee bottomed boats just paint a strip below the waterline and call it job done? 

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5 minutes ago, Bee said:

Wet steel will corrode - badly and sometimes very quickly. 

Rust, or oxidiation, requires air and water. There's not much air 2ft6in below the surface.

If you do want to paint it, then do as much as you can reach this time, and put your supports in a different position next time. This way you cover all of it over time

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11 minutes ago, Bee said:

 Do people with sailing boats, round bilge or vee bottomed boats just paint a strip below the waterline and call it job done? 

 

16-10-19h.jpg

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1 hour ago, Machpoint005 said:

 

My point, succinctly put!

 

 

 

 

Surely better to do most of the base plate than none? The bits resting on supports can be done the next time.

 

Haggis

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1 minute ago, Alan de Enfield said:

 

16-10-19h.jpg

That picture is posed! Look at the bloke, not a mark on him, last time I painted the boat I had to bath in white spirit and burn all my clothes.

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32 minutes ago, Ex Brummie said:

There's not much air 2ft6in below the surface

Do the fish know this?

With severe pitting after 9 years I would be checking my (and my neighbourhood's) electrics.

I don't paint the exterior of my baseplate. I will wear out faster than it will.

Edited by system 4-50

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Definitely!
When I bought Midnight as a shell the builder said no need to black the baseplate there's no oxygen down there to corode it (BTW tell that to the fish) . 8 years later after welding about 150  to 200 3mm & 4mm pits I had the baseplate sand-blasted and two-packed it - never had a problem since. Older boats with high quality steel seem to get by but with the crap foreign steel that's about now I wouldn't think twice about blacking the baseplate. Basically it'll cost about an extra £120. Over-plating costs a lot more than that!

Edited to add - I use a 20 ton jack to move the stanchions so the whole plate gets done

 

Edited by Midnight

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1 minute ago, system 4-50 said:

Do the fish know this?

Yes. That’s why they live underwater and humans don’t. There is no air underwater but there is a small amount of dissolved oxygen. It’s at a ratio of about 1 part in 100 whereas in air it is about 1 part in 5. @Ex Brummie was quite correct. Hence steel rusts far more readily in air than it does in water.

 

However it isn’t really pure environmental corrosion that is the worry with a boat. Rusting happens slowly even in air to a point where it probably wouldn’t be that much of a concern even for the side plates given the thicknesses concerned and the projected lifespan of a narrowboat.

 

However the environment in which any narrowboat exists is something of an unknown in terms of the potential for electrolytical or chemical corrosion and that’s because they sit in water.
 

Painting is a universal method for preventing corrosion of steel so if you can paint your baseplate it’s best to do so.

 

It’s also a fact that the vast, vast majority of narrowboats never have their baseplates painted and that’s the principal reason they are manufactured from thicker steel than the side plates (which in theory are more susceptible to corrosion). There are many steel boats out there in their fifth decade or more now and we see no great evidence of boats sinking due to rusted baseplates. So it’s equally the case that if you cannot access the baseplate to paint it then it should be no matter of great concern.
 

That’s not to say there isn’t an issue of cost effectiveness in terms of potential costs for overplating but overall I think there is no straight answer to the question posed. It’s largely down to the appetite for risk, value of the boat concerned and available funds of the owner.


My boat has had its baseplate painted in the past but I have not had it done on either of the two occasions I have had it blacked.

 

JP

  • Greenie 1

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1 hour ago, Bee said:

>>Wet steel will corrode<<

It corrodes much faster where there is a ready oxygen supply. That's why the hull rusts first at the waterline - not a foot or two below the waterline.

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Taken from last October's survey of our 35 year old boat:

Quote

The bottom plates were originally painted with a protective paint system after grit blasting in 1987, this has held up well but, is now nearing the end of its working life and consideration should be given to having it re-applied.
The thickness readings measured and typical pitting measured are what I would expect to find on a vessel of this age with a painted bottom. In my opinion the bottom plates are fit for purpose.

Suggestion:
It would be beneficial to have the bottom plates pressure washed and the protective paint system reapplied, this would ensure further deterioration is minimised.

 

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