Not blacking the bottom...

[lewisericeric]

What's everyone's thoughts on boat builders who build boats and black at build stage, but state that they don't black the very bottom of the hull? Is this standard practice? 

[Guest]

5 minutes ago, lewisericeric said:

What's everyone's thoughts on boat builders who build boats and black at build stage, but state that they don't black the very bottom of the hull? Is this standard practice? 

 

If not 'standard' practice, it seems to be very common to leave the base plate un blacked and subsequently not have it blacked at the same time the rest of the hull is done. 

[lewisericeric]

I've heard arguments about it being so far under the water there's no oxygen etc. etc., but is this wise or not?

[Alan de Enfield]

1 minute ago, lewisericeric said:

I've heard arguments about it being so far under the water there's no oxygen etc. etc., but is this wise or not?

 

I can only say I've never had a NB bottom blacked (40 years and about 12 NBs)

 

The last NB I had that went in for blacking I asked about the bottom and was told it was immaculate and was 13mm thick - it had been built with 12mm (nominal) steel so had lost nothing in 20 years of use and not being blacked

[Tracy D'arth]

Fish still breath on the bottom.

 

The other old wives tale is that boats don't rust in winter because its colder.

 

Having seen too many badly pitted baseplates I am a believer in grit blast and epoxy the same as the hull sides.

 

I have also seen too many open seam butt welds that have never been welded. Welding one side is easy, turning it over to weld the other side is often neglected. Leave that in the water and it matters not how thick the plate is, it can be just a few millimetres thick on that weld. The result of corrosion is just the same, down she goes. 

[Guest]

10 minutes ago, lewisericeric said:

I've heard arguments about it being so far under the water there's no oxygen etc. etc., but is this wise or not?

 

As Alan indicates the base plate is normally a lot thicker than the hull sides so there is a lot of steel to get through before it became an issue (if it did corrode).

 

You would likely soon scrape large bits of your bottom blacking off on most UK canals anyway.

 

 

[Tracy D'arth]

1 minute ago, The Happy Nomad said:

 

 

 

You would likely soon scrape large bits of your bottom blacking off on most UK canals anyway.

 

 

True, but you only scrape the high spots, not the pits, which are what matters.  Epoxy is surprisingly resistant to abrasion.

[Tonka]

13 minutes ago, lewisericeric said:

I've heard arguments about it being so far under the water there's no oxygen etc. etc., but is this wise or not?

Recently had my boat surveyed and the surveyor recommended that next time I should black the bottom plate. Lots of misinformation out there.

1) there is no oxygen down there. WATER is H2O. so there is

2) it will scrape off. It scrapes off the side on lock walls but we still paint it

3) it is not usually done. That is because most boatyards do not have the facilities for it to be done. 

4) it is the largest area of the hull so why not

[rusty69]

In contrast, I always try to black our base plate, but it was only built with a 6mm base plate. If I changed my boat every 3 years, I probably wouldn't bother. But as I have had the same boat for 23 years I feel it is worth doing.

 

If I was having a new boat built today, I would probably specify some kind of epoxy coating or a 12mm base plate.

 

If they state they are not going to black it, I can't see the problem. Either specify that they do it as an extra if you want it done, or do it yourself before it's launched.

 

Not sure what fish breathe, but I'm sure some of them exist lower than a baseplate of a typical inland waterways boat.

[Guest]

10 minutes ago, Tracy D'arth said:

Fish still breath on the bottom.

 

The other old wives tale is that boats don't rust in winter because its colder.

 

Having seen too many badly pitted baseplates I am a believer in grit blast and epoxy the same as the hull sides.

 

I have also seen too many open seam butt welds that have never been welded. Welding one side is easy, turning it over to weld the other side is often neglected. Leave that in the water and it matters not how thick the plate is, it can be just a few millimetres thick on that weld. The result of corrosion is just the same, down she goes. 

 

The challenge though is doing it. Steel NB's are normally built from the baseplate up, often sat flat on the workshop floor or very close to it. And then at subsequent blackings the boat sits on bearers and would have to be moved to expose all of the base plate. I know it can be done but it would add to the cost I suspect.

Edited May 26, 2022 by The Happy Nomad

[Tracy D'arth]

Just now, The Happy Nomad said:

 

The challenge though is doing it. Steel NB's are normally built from the baseplate up, often sat flat on the workshop floor or very clode to it. And then at subsequent blackings the boat sits on bearers and would have to be moved to expose all of the base plate. I know it can be done but it would add to the cost I suspect.

Debdale Wharf do it without drama, and at a sensible price too.

[Guest]

11 minutes ago, Tracy D'arth said:

Debdale Wharf do it without drama, and at a sensible price too.

 

How do they move the boat? Or the bearers?

 

They (only) charge around six quid more per foot to do the base which seems like a reasonable price. £360 more for our old boat. 🤔🤔

Edited May 26, 2022 by The Happy Nomad

[BWM]

23 minutes ago, The Happy Nomad said:

 

As Alan indicates the base plate is normally a lot thicker than the hull sides so there is a lot of steel to get through before it became an issue (if it did corrode).

 

You would likely soon scrape large bits of your bottom blacking off on most UK canals anyway.

 

 

Even though a thicker baseplate is undoubtedly more resistant to corrosion it is still an issue for insurers, as they work on percentage of depth of pitting to original thickness. 

 

[Tracy D'arth]

The boat is jacked up on movable stocks to overhead height. Then thin tubular stands are placed around the edge and moved as the work progresses

They achieve 100% coverage during grit blasting, spot pit welding, zinc spraying and epoxy 2 coats. You get a memory stick with all the stages photographed.

Its impressive for the money.  Recently around £2K for a 50' boat.  10 year guarantee too.

[Mike Tee]

35 minutes ago, The Happy Nomad said:

 

 

 

You would likely soon scrape large bits of your bottom blacking off on most UK canals anyway.

 

 

Not true - my previous boat was about 2’8” draught and the base had been blacked before my ownership, and during it (at Debdale). It was a well used boat on a variety of waterways and each time it came out of the water (for whatever reason) I checked the baseplate - it showed absolutely minimal damage to the blacking.

[Guest]

1 minute ago, Mike Tee said:

Not true - my previous boat was about 2’8” draught and the base had been blacked before my ownership, and during it (at Debdale). It was a well used boat on a variety of waterways and each time it came out of the water (for whatever reason) I checked the baseplate - it showed absolutely minimal damage to the blacking.

 

I rode over enough shopping trolleys and other cr@p to believe it extremly likely our blacking (if it had been done) would have been damaged.

[jonesthenuke]

2 minutes ago, The Happy Nomad said:

 

I rode over enough shopping trolleys and other cr@p to believe it extremly likely our blacking (if it had been done) would have been damaged.

When we last blacked out boat there were plenty of scrape marks on the baseplate, mostly towards the stern where it is deeper. Travelling the BCN may have something to do with this.......

[beerbeerbeerbeerbeer]

26 minutes ago, The Happy Nomad said:

 

I rode over enough shopping trolleys and other cr@p to believe it extremly likely our blacking (if it had been done) would have been damaged.

After inspecting under my boat this year I saw lots of pitting, pretty much all in lines from bow to stern, where I had scraped along over stuff. 
In 10 years it’d never been painted. 
So this year I have epoxied it. 
Fortunately the boat was craned to another part of the yard and I was able to get the bits I’d missed because of the bearers having being in the way. 
 

As others have said, in theory I should only scratch the high parts and hopefully the paint will stay nice and solid in the pits. 
 

I now think it very odd that someone would spend £200,000, or whatever, on a new boat build and not get the bottom painted. 

[Guest]

6 minutes ago, Goliath said:

I now think it very odd that someone would spend £200,000, or whatever, on a new boat build and not get the bottom painted. 

 

Or you you could put it another way and ask why builders selling such expensive boats don't routinely black the base plate?

[beerbeerbeerbeerbeer]

I don’t know why they don’t do it. 
That’d be a question I’d ask if I were having one built. 
 

So at what point do builders lift a boat on to bearers?

As soon as the shell is finished?

 

[lewisericeric]

Thanks for the input guys. As always on Canal World, lots of differing theories there 😂

[blackrose]

I've never painted my baseplate apart from about 6ft back from the upswept bit at the bow. However, that's all changing this year and I plan to blast and epoxy the whole thing.

 

Different people will tell you different things, but to a well respected boat painter at my mooring has told me he's blasted through a few baseplates that started out at 10mm and the steel loss wasn't due to physical wear. Perhaps there was some galvanic corrosion, I'm not sure.

 

Anyway at the end of the day, my view is the more paint you can get on a steel hull the better - with the caveat that if you are painting the baseplate then you also need to paint the parts hidden by the wooden beams that the boat rests on, because if you don't those areas may act like anodes. 

2 minutes ago, lewisericeric said:

Thanks for the input guys. As always on Canal World, lots of differing theories there 😂

 

That's what it's all about. Listen to different views then make your own mind up.

[roland elsdon]

31 minutes ago, Goliath said:

I don’t know why they don’t do it. 
That’d be a question I’d ask if I were having one built. 
 

So at what point do builders lift a boat on to bearers?

As soon as the shell is finished?

 

Often not at all. You are assuming they weld both sides. Not all do.
V the plate and then seam weld. Bit like tacked on rubbing guards. Lovely rust encourager.

[blackrose]

2 hours ago, Tonka said:

Recently had my boat surveyed and the surveyor recommended that next time I should black the bottom plate. Lots of misinformation out there.

1) there is no oxygen down there. WATER is H2O. so there is. I think your surveyor is confusing H20 with dissolved oxygen. The strong covalent bonds within H20 mean that the oxygen molecules are not available for the electrochemical process that causes steel corrosion.  On the other hand dissolved oxygen is what fish breath and does cause corrosion.

2) it will scrape off. It scrapes off the side on lock walls but we still paint it

3) it is not usually done. That is because most boatyards do not have the facilities for it to be done. 

4) it is the largest area of the hull so why not

 

But other than that I completely agree with your surveyor.

 

3) Is also the same reason most canal boatyards still slap on bitumen instead of prepping the hull properly and applying long lasting epoxy. Like many narrowboaters they are still stuck in the dark ages.

Edited May 26, 2022 by blackrose

[MtB]

2 hours ago, Tracy D'arth said:

Epoxy is surprisingly resistant to abrasion

 

That's surprising!