Pitting

[Manxcat54]

Hi

This is my first post, so go easy on me. I know you are sick of all the I'm looking for a cheap boat stories, however,  I have purchased a 55ft with a survey which says base plate 9.3mm at lowest, but side plates pitted at wind and water line, advise over plating, but lowest readings were all over 4mm. Could I sail this if I clean it and black it.

Thanks

Malc

[Jen-in-Wellies]

Welcome to the forum. 4mm is the minimum hull thickness that most insurance companies are happy to give comprehensive insurance to. At some point the pitting needs dealing with. Once it starts, corrosion gets concentrated within the pit, so they tend to go deeper over time. 

[Manxcat54]

I believe you can fill the big pits in with a pool weld

[Jen-in-Wellies]

I've seen it done yes. Time consuming and requires skill and care, so still expensive if you are paying some one else to do it and needs good welding experience if it is you. 

[Manxcat54]

There's a welding shop next door to me

[Tony Brooks]

Just now, Manxcat54 said:

There's a welding shop next door to me

 

Maybe, but will it be next to the boat when it is out of the water? If not, do they do mobile site work and will whoever gets the boat out allow them on site? All things that need considering.

[Manxcat54]

The boat is on hard standing in front of the welding shop, so that's a plus

[David Mack]

If the hull is grit blasted and epoxied that should stop any further corrosion of the pits.

[Manxcat54]

Thanks David,  I feel a bit better now 

[Tony Brooks]

6 minutes ago, Manxcat54 said:

Thanks David,  I feel a bit better now 

 

It might be in your best interest to consider the possibility that some pits MIGHT be microbial corrosion and if so grit blasting might not get rid of it, it might need further processes. If it is microbial corrosion, then it may stay active under the said epoxy, deepening the pit and making the coating fall off. It seems many yards do not yet understand microbial corrosion.

[Alan de Enfield]

9 minutes ago, Manxcat54 said:

Thanks David,  I feel a bit better now 

 

Before you get too relaxed - check out the price of blasting and epoxy. It is not cheap (£000's, not £00's) It is many times the cost of 'blacking', but, yes it does a much better job if applied properly.

The next issue is finding a yard that does it - blasting it is a messy job and not many places will do it.

[Stroudwater1]

Many refer to it as pit welding. So long as it’s treated pit welded epoxied and ideally the boat lifted and checked every couple of years it should be OK. 

The sides have corroded more haven’t they? possibly from electrical currents in the water. A galvanic isolator should help, hopefully there is one and it works? 
 

Many people recommend Debdale wharf. They do seem to have a good set up. Ideally best to have the baseplate epoxied too though you’ve not lost much so far there. It’s pricy but keeping your hull in good shape is a good investment I where possible with cost. 
 

Overplating is probably unnecessary if the above is done, it’s got downsides and sometimes is not done too well. 

[Bee]

In my opinion, your 1st problem is what paint to use, if this boat has had bituminous paint slapped  on then its not particularly good stuff, its banned in many countries because its toxic but its protection doesn't last very long, it dissolves when faced with diesel on the water and lots of other solvents it really is only OK above the water line, unfortunately the modern epoxy paints don't work too well if applied over bituminous paint either so there is a good case for removing as much as you can along the water line by hand, twisted wire cup brushes on grinders are apparently successful but I haven't tried, when the surface is as good as you can get it then a 'Surface Tolerant' epoxy like Jotun 90 (?) is the way to go. It is laborious, dirty, time consuming and just plain horrible but cheaper than blasting. As for the underneath it may never have been painted so perhaps just pressure wash and do the best you can. Jotun might even do a primer that covers bituminous paints these days but I don't know.

[doratheexplorer]

It's worth trying to find out what specifically caused the pitting in the first place.  For example, if the boat is fairly new or has been looked after well by regular blacking, use of a galvanic isolator etc. and it's still badly pitted then I'd be pretty concerned that either the steel is poor quality or that there are significant issues with the electrical set up of the boat.  Either way you can look forward to ongoing problems with corrosion.

 

On the other hand, if the boat is old, perhaps been neglected, maybe has been stuck in a marina for years on a hook-up, with no galvanic isolator, or maybe even kept in brackish water, then pits down to 4mm would seem perfectly reasonable and it would therefore be reasonably to presume that looking after the boat well in future would prevent significant further corrosion.

[TandC]

My view on it is if I were looking at that boat,  as it stands, it is on the cusp of not being insurable - therefore, it has to have some steelwork done - slapping on some paint (epoxy or otherwise) wouldnt feel like a very sustainable solution for the long-term.  There are so many second hand boats out there - it'd have to be a really good deal to make buying a lemon worth the faff.    Perhaps there's some real benefits to this one - it's local, out the water already, near a welder, etc.    You want to get the welding done (overplating or pits), and then the gold standard would be to shotblast and epoxy.  

Ours is now 25 years on from having been overplated and epoxied.  Those costs have been totally worth it. 

 

 

[MtB]

3 hours ago, Alan de Enfield said:

The next issue is finding a yard that does it - blasting it is a messy job and not many places will do it.

 

Also, its never a good idea to have one's own boat out of the water at a yard that grit blasts other boats, in case they grit blast the boat on the hard next to yours. DAMHIK.

 

ABC at Aldermaston are a good one to avoid if having your boat deluged with grit would bother you. 

 

 

[Lady M]

We got swarf (steel crumbs) on our boat from work done on the one alongside when it was out of the water at a yard.

[LadyG]

8 hours ago, Manxcat54 said:

There's a welding shop next door to me

Ask them for advice, assuming it's a boatyard

[beerbeerbeerbeerbeer]

9 hours ago, Jen-in-Wellies said:

I've seen it done yes. Time consuming and requires skill and care, so still expensive if you are paying some one else to do it and needs good welding experience if it is you. 

I’ve seen it being done and they seem to crack on with it. 
Probably very monotonous to do mind. 
Costs would simply be an hourly rate plus price of rods,

in the scheme of things perhaps not expensive 🤷‍♀️

Edited January 25 by beerbeerbeerbeerbeer

[blackrose]

9 hours ago, Tony Brooks said:

 

It might be in your best interest to consider the possibility that some pits MIGHT be microbial corrosion and if so grit blasting might not get rid of it, 

 

Does anyone understand how microbes are able to resist grit blasting? Intuitively it doesn't sound feasible.

[Tony Brooks]

I say "better safe than sorry" if a wash down with bleach or similar, possibly after a pressure wash and before blasting. I don't see how one can be 100% sure the pieces of grit will hit all the pit surfaces, especially if the microbes have undercut it. I would have thought the pieces of grit would be much larger than a microbe, but would likely cause the rust to flake off, so not all the surface would be hit.

[blackrose]

Rusty69 of this forum had his hull pit welded last summer. I saw the result which looked pretty good. 

 

Although it's true that pitting is sometimes due to galvanic or microbial corrosion, the cause of the vast majority of pitting of steel boats on the canals is far more mundane and is simply the result of neglect. So while it's worth checking any mains earth isolation (assuming it's been on shore power), personally I wouldn't let these things worry you unduly.

 

if you do buy the boat and get it for a price that reflects the condition of the hull, then grit blasting, pit welding and several coats of a good epoxy seems like a good approach.

[LadyG]

6 hours ago, TandC said:

My view on it is if I were looking at that boat,  as it stands, it is on the cusp of not being insurable - 

 

I think we are getting in muddy waters, the OP needs to insure in order to get a CRT Licence, however that can be third party, not comprehensive.

I suggest OP stop posting on the forum about this, insure the boat, and then sort out the problems.

With respect to killing microbes, it is impossible to sterilise the hull of a boat. Yes you could do your best, but that may not be good enough, you cannot be 100% sure 

Buying any boat caries a degree of risk.

 

 

 

 

Edited January 25 by LadyG

[blackrose]

7 minutes ago, Tony Brooks said:

I say "better safe than sorry" if a wash down with bleach or similar, possibly after a pressure wash and before blasting. I don't see how one can be 100% sure the pieces of grit will hit all the pit surfaces, especially if the microbes have undercut it. I would have thought the pieces of grit would be much larger than a microbe, but would likely cause the rust to flake off, so not all the surface would be hit.

 

Any decent grit blasting takes off the whole surface. It's not like only one piece of grit hits a particular tiny area. Anyway, don't these microbes live in wet or at least moist conditions? Most microbes can only live in certain conditions otherwise they die - unless they're like spores which can remain dormant? I personally wouldn't put bleach on a grit blasted hull as you're more likely to be adding contaminants to the surface and the last thing you want after you've grit blasted is to wash the hull with water and start it rusting.

[LadyG]

PS you have had the boat surveyed, if the surveyor has advised overplating then you may have to be a bit circumspect, the surveyor may be correct, he wears belt and braces, but overplating is likely not going to increase the value of the boat [be aware of the extra weight and the height of the engine vents].

You have knowingly bought a cheap boat, presumably because you have a limited budget, and weighed up the risks before the survey.

Personally, I would spend some time working on the boat, inside and out, hopefully there is no rush, it's too cold and wet to get a good dry surface.

Once you start paying professionals you will learn why BOAT stands for Bring Out Another Thousand.

 

There is nothing to stop you discussing these things with the surveyor and with the welder.

 

Edited January 25 by LadyG