Overplate or not

[Tiberian]

Hey guys a bit of advice really a 1988 narrowboat just had a survey and surveyor recommended both sides to be overplated he said there was pitting to the sides 1.5mm deep, this course of action seem exesive and unnecessary to me am I being naive or would shot blast the hull, puddle weld the worse of it and 2 pack epoxy the lot be more appropriate 13mm bace plate 6mm sides thank you

[Alan de Enfield]

8 minutes ago, Tiberian said:

Hey guys a bit of advice really a 1988 narrowboat just had a survey and surveyor recommended both sides to be overplated he said there was pitting to the sides 1.5mm deep, this course of action seem exesive and unnecessary to me am I being naive or would shot blast the hull, puddle weld the worse of it and 2 pack epoxy the lot be more appropriate 13mm bace plate 6mm sides thank you

 

He is probably working on the fact that your minimum thickness is 4.5mm and insurers will not give comprehensive cover once you get down to 4mm.

You need to start thinking about taking some action to rectify it, but can you guarantee to get all the pits if you go for spot-welds, vs do you really need to overplate and think how that affects you draft and clearances for hull openings

 

What size boat is it ?

Overplating on (say) a 35 foot boat has much more affect on stability than overplating on a 60 foot boat.

 

 

[Stroudwater1]

It depends as Alan says, it maybe easier to know what’s needed once the boats been grit blasted. The situation will be unlikely to be completely clear until the boat is assessed with all the crud blased off.
 

you will probably get different views here, some say it’s likely to last for years before getting to zero mm others will say get it overplayed. 
 

Pit / puddle welding is often fine with epoxy (plus the baseplate if possible). That will slow down rusting greatly . You will ideally still need to have the hull inspected every couple of years. 
 

[MtB]

15 minutes ago, Alan de Enfield said:

What size boat is it ?

Overplating on (say) a 35 foot boat has much more affect on stability than overplating on a 60 foot boat.

 

Also, what is it worth? 

 

An old 1988 boat is not necessarily worth insuring comprehensively if £20k of overplating is needed and the insurer says it is worth only £15k in the event of a total loss.

 

Third party insurance costing a pittance might be more appropriate.

 

 

 

 

Edited October 1, 2023 by MtB

[Tiberian]

Narrowboat is 62ft

 

[Slim]

For what it's worth, having experienced significant pitting on a 4 to 5 year old boat around the  year 2000. (approx 1.5 to 2 mm on 6 mm sides) I would go down the blast and pit weld route. That's what I did. A hull survey this time last year found nothing below 5.7 mm. 

[Tracy D'arth]

Overplating will seriously reduce the value of the boat in my view. I would never buy one, you would not know how well it was done.

It would reduce the freeboard necessitating ballast removal. With a 13mm baseplate there may not be a lot of ballast that could be removed.

 

If the baseplate is good and at 13mm it is better than most, I would pit weld extensively and epoxy, or even take it to Debdale Wharf and have it grit blasted, hot zinc sprayed and epoxy coated. You would get a 10 year guarantee then. Expensive but you end up with a good boat hull.

 

If the pitting is mainly on the water line you could consider having an extra rubbing strip welded on to cover the pits, continuously welded top and bottom of course.

[blackrose]

43 minutes ago, Tracy D'arth said:

Overplating will seriously reduce the value of the boat in my view. I would never buy one, you would not know how well it was done.

 

If the pitting is mainly on the water line you could consider having an extra rubbing strip welded on to cover the pits, continuously welded top and bottom of course.

 

Doesn't the second statement contradict the first to some degree? How would you know (as a buyer) how well it was done any more than overplating?

 

1 hour ago, Slim said:

For what it's worth, having experienced significant pitting on a 4 to 5 year old boat around the  year 2000. (approx 1.5 to 2 mm on 6 mm sides) I would go down the blast and pit weld route. That's what I did. A hull survey this time last year found nothing below 5.7 mm. 

 

What had happened to it in its first 4 or 5 years to cause 2mm pitting? Plugged into shore power with no isolation?

Edited October 1, 2023 by blackrose

[rusty69]

It sounds a similar situation to our boat. It will depend how many pits, and the thickness of the original steel and how important fully comp insurance is to you. 

 

Our pits were not too numerous, so we had them individually welded earlier in the year before applying epoxy coating ourselves. 

 

 

Also worth considering the condition of the plate on the inside of the boat of you have access to inspect it. 

[Morris]

10 hours ago, Alan de Enfield said:

 

He is probably working on the fact that your minimum thickness is 4.5mm and insurers will not give comprehensive cover once you get down to 4mm. 

 

 

I've asked this before but got no answer: Are there particular insurers who say this or is it just a scare story on here? 

I spoke to a number of different insurers when insuring our boat and they made no such stipulation (I asked specifically) and were only concerned that any remedial action suggested in the survey was completed.

(I get in ops case that means overplating but our survey identified some deeper pits than that and no welding work was recommended). 

 

To op - overplating 6mm sides because of 1.5mm deep pits seems like madness to me. 

 

[Bee]

A good many steel boats are only built with 4 mm plate from new, smaller cruisers and such like. Steel is pretty tough stuff and narrowboats are massively strong so we are really talking about sinking when the steel rusts through. Pits are not great but a decent coat (or more) of epoxy will stop them being active. I wonder if epoxy filler as a treatment for a few pits is a good idea? I think your surveyor is being a bit hasty regarding a big overplating job, personally i would treat the pits if possible and not worry overmuch.

[Troyboy]

13mm baseplate on a 1988 built boat makes me wonder if the baseplate has already been overplated as there weren't many boat builders using 13mm plate in 1988. In reply to the question I agree with Morris no need to overplate 6mm sides because of 1.5mm pits.

[David Mack]

1.5mm pits on a 13mm bottom. Thats barely more than 10% loss over 35 years. Absolutely no need to overplate that, or to do anything really although, although a proper blast clean and epoxy would put a halt to further corrosion.

[Col_T]

13 hours ago, Tiberian said:

pitting to the sides 1.5mm deep

 

[Tacet]

13 hours ago, Alan de Enfield said:

 

 

What size boat is it ?

Overplating on (say) a 35 foot boat has much more affect on stability than overplating on a 60 foot boat.

 

 

Why is this, please?

[cuthound]

11 minutes ago, Tacet said:

Why is this, please?

 

Because the weight of the overplating is a greater proportion of the boats overall weight when the boat is shorter.

[alan_fincher]

Who was the builder of this1988 62 foot narrow boat please?

I would have thought that a 13mm baseplate was pretty unusual back then.

[noddyboater]

54 minutes ago, alan_fincher said:

Who was the builder of this1988 62 foot narrow boat please?

I would have thought that a 13mm baseplate was pretty unusual back then.

Our 1988 was built with a 13mm baseplate, but it's a Five Towns (R. Fuller) so not exactly a volume builder.

Don't forget that not long after when steel was comparatively cheap up to 25mm baseplates were used. 

[Tacet]

1 hour ago, cuthound said:

 

Because the weight of the overplating is a greater proportion of the boats overall weight when the boat is shorter.

Would that not impact more on the draft rather than stability?

[ditchcrawler]

4 minutes ago, Tacet said:

Would that not impact more on the draft rather than stability?

The weight wont be at the bottom unless its a base plate thats overplated 

[cuthound]

3 minutes ago, Tacet said:

Would that not impact more on the draft rather than stability?

 

Yes, and by lowering the freeboard the hull openings get closer to the water, making water ingress more likely. You then have to remove ballast to compensate, which isn't always possible in a small boat.

 

A small narrowboat sank in the Thames because the engine air inlet vent went under water after being replated and had two people and a dog on the stern.

[Tacet]

OK - overplating has a greater effect on draft on a shorter boat than a longer one, all other things being equal.

But typically not stability, in any conventional sense that is.

[Mike Tee]

For a 1988 boat it might well be 1/2” plate originally.

[Slim]

16 hours ago, blackrose said:

 

Doesn't the second statement contradict the first to some degree? How would you know (as a buyer) how well it was done any more than overplating?

 

 

What had happened to it in its first 4 or 5 years to cause 2mm pitting? Plugged into shore power with no isolation?

Never really got to the bottom of it. At the time i was fitting it out and wasn't permanently plugged in (only when I was using 230v tools etc on extension leads). I suspect it was a nearby, fairly new, Colecraft with liveaboards. The strangest thing was that on one side about 6" above the baseplate there was a perfect 'pit' in the form of a cross exactly as one would imagine a fabricator marking a spot with a sharp instrument  such a file or screwdriver. The hull had been blacked from new by the builder. I sat on a low stool with a welder, a grinder with a wire wheel and another grinder with a grinding wheel for two days. Quite enjoyed myself.😇

[Alan de Enfield]

3 minutes ago, Slim said:

Never really got to the bottom of it.

 

Had you considered Microbial Corrosion, it has been shown to develop pits that can actually penetrate a thick-hulled commercial vessel in 18 months

 

It is now becoming quite widely found on the canals and more and more cases of attack on steel NBs are being reported.