How much pitting is OK?

[Suki Sjodahl Staples]

My partner and I are looking to purchase a widebeam and we recently reviewed a survey of one we may be buying. As we are new to boating we want to ensure we aren’t making any mistakes and read in the report that the steel hull has some historic pitting. The deepest one reaches 1.6mm and it states that if it reaches 2mm they will have to be ground out and pad welded over .. I was just wondering if this depth of pitting should be of a big concern or not?

thanks for any help! 

[Tony Brooks]

I think you had better give the type of boat and the hull and base plate specification. If it's Dutch it may only have a 3 or 4mm hull. If its a so called wide beam narrowboat the "historic" is not a word I would expect to apply and as they tend to be 6mm sides and 10mm or more base plate I would not be worrying over much about welding until the pits were 4mm deep or more on the base plate. I would however be taking steps to minimise further corrosion.

[Alan de Enfield]

6 minutes ago, Suki Sjodahl Staples said:

My partner and I are looking to purchase a widebeam and we recently reviewed a survey of one we may be buying. As we are new to boating we want to ensure we aren’t making any mistakes and read in the report that the steel hull has some historic pitting. The deepest one reaches 1.6mm and it states that if it reaches 2mm they will have to be ground out and pad welded over .. I was just wondering if this depth of pitting should be of a big concern or not?

thanks for any help! 

How long ago was the survey done ?
Who did the survey & why ?

 

If it was the seller then the surveyor would be acting on his behalf and it would be 'normal' to minimise the problems

If it was on the behalf of a buyer - why did the buyer not go ahead ?

 

If it is a 15mm base plate then don't worry.

If it is a 2.0mm base plate - run away quickly keeping your cheque book in your pocket.

Edited September 5, 2018 by Alan de Enfield

[dmr]

4 minutes ago, Tony Brooks said:

I think you had better give the type of boat and the hull and base plate specification. If it's Dutch it may only have a 3 or 4mm hull. If its a so called wide beam narrowboat the "historic" is not a word I would expect to apply and as they tend to be 6mm sides and 10mm or more base plate I would not be worrying over much about welding until the pits were 4mm deep or more on the base plate. I would however be taking steps to minimise further corrosion.

 

The term "historic" is used to suggest that the pitting has occurred in the past but is no longer active, though not sure how the surveyor can be certain of this. Epoxy should pretty much stop any further pitting.  I used to live in a house with severe historic subsidence but I reckon it was still moving.

 

It is possible to also get pitting from the outside in and you just have to hope than an outside in pit never meets up with an inside out pit.

 

............Dave

[Bee]

If you look at a ruler and work out what 1.6mm looks like it really is not very much, but, and there always is a but, you need to make sure that the other side of the plate is OK, floorboards need to be lifted and I bet they are fixed down. Most boats that are a few years old have some scabby bits somewhere and most surveys have some faults pointed out. As Tony says, take steps to minimise further corrosion, even if you buy another boat. Modern paints are really pretty good and will stop steel returning to nature. It is alarming how fast steel can corrode if it is not painted, some boats just seem to corrode, some don't but both will do better with paint on them. Personally I would not be bothered much by a few pits unless the boat started life with very light steelwork.

[MtB]

3 hours ago, dmr said:

It is possible to also get pitting from the outside in and you just have to hope than an outside in pit never meets up with an inside out pit.

 

Eh? Is not 99% of all pitting from the outside in?

 

Have you been on the northern medicine again?!

 

[dmr]

16 minutes ago, Mike the Boilerman said:

 

Eh? Is not 99% of all pitting from the outside in?

 

Have you been on the northern medicine again?!

 

 

I have some inside out pitting under my battery box, some on the integral water tank baseplate, and probably lots more that I don't know about. A boat welder recently suggested that older boats, especially wet bilge types, rust from the inside out, but that most more recent boats rust from the outside in. Others say that most boats rust from the inside out. What is the balance from that steel section that you have in your black museum????

 

No alcohol at all last night, gentle night in on the cider tonight, this will be two consecutive nights without going to the pub, the first time this has happened since we arrived here!

 

Its good up here but its already getting cold, I doubt the stove lighting will last till October like it does down South.

 

..............Dave

[MtB]

2 minutes ago, dmr said:

What is the balance from that steel section that you have in your black museum????

 

 

Hmmm that is just randomly and extensively corroded all over on both sides. The holes being where low points on both sides coincide.

 

The pitting I've seen on modern boats is quite different from general corrosion like my hull sample. Distinct, discrete and tightly defined blind holes in the hull, with the surrounding metal broadly unaffected, and typically 2 to 3mm across and 2 to 3mm deep. Almost like someone has been at the hull with a drill. 

[dmr]

4 minutes ago, Mike the Boilerman said:

 

 

Hmmm that is just randomly and extensively corroded all over on both sides. The holes being where low points on both sides coincide.

 

The pitting I've seen on modern boats is quite different from general corrosion like my hull sample. Distinct, discrete and tightly defined blind holes in the hull, with the surrounding metal broadly unaffected, and typically 2 to 3mm across and 2 to 3mm deep. Almost like someone has been at the hull with a drill. 

 

There you go! the inside out and the outside in met in the middle ?

 

We have some pitting as you describe on the sides, mostly well below the waterline, though nowhere near 3mm deep. That's why we are now using epoxy. When we first blacked the boat the  dry dock bloke had a look and said it was pretty common and he had seen it on almost new boats. I wonder if some of it is related to the mill scale coming off??

 

..................Dave

[MtB]

9 minutes ago, dmr said:

There you go! the inside out and the outside in met in the middle ?

 

Yes. And the holes are in a baseplate fitted in 1917 (approx), if I understand Pete Harrison correctly! Definitely not pitting.

[Suki Sjodahl Staples]

Thanks so much for all your help. The survey was done by the seller April 2018. 

It is a 57 x 10” liveaboard widebeam built by Liverpool Boat co in 2003. The Hull is welded steel 10mm/6mm/5mm. They did not have access to the interior of the hull except for the engine room. I have attached a couple of photos of the corrosion from the survey. 

[Richard10002]

Looks like no big deal to me......

[Tony Brooks]

7 hours ago, Richard10002 said:

Looks like no big deal to me......

I tend to agree. I think it is a true description of the pits written in a way that may facilitate negotiation on price.

 

I would just keep an eye on it but if I could afford it I would get it shot blasted or similar and two pack coated..

[Alan de Enfield]

It would be unusual for the steel thicknesses to have increased since manufacture - I wonder how, if the 'sides' thickness is NOW 6.1 - 6.9mm he can state that it was originally 6.0mm, and similarly the current 10.9mm base plate was originally 10.0mm.

 

The report was undertaken on behalf of the vendor (not a buyer) so it will tend to be more on the 'no problems, conservative' side, but it certainly looks as if there is nothing to be overly worried about.

[Sea Dog]

6 minutes ago, Alan de Enfield said:

It would be unusual for the steel thicknesses to have increased since manufacture - I wonder how, if the 'sides' thickness is NOW 6.1 - 6.9mm he can state that it was originally 6.0mm, and similarly the current 10.9mm base plate was originally 10.0mm.

 

 

The more basic thickness meters can't allow for coatings, etc, to measure just the steel. I suspect this surveyor was using one of those.

[Alan de Enfield]

7 minutes ago, Sea Dog said:

The more basic thickness meters can't allow for coatings, etc, to measure just the steel. I suspect this surveyor was using one of those.

I would hope that a surveyor would not be using a 'basic thickness meter' that can be obtained from ebay for £1-10/6.

The gauge used was a professional quality gauge "which is suitable for measuring thickness and Corrosion of ships hulls " (manufacturers quote) and has both accuracy and resolution to 0.1mm

 

The report also makes mention that the base plate was NOT blacked.

[MtB]

49 minutes ago, Alan de Enfield said:

I would hope that a surveyor would not be using a 'basic thickness meter' that can be obtained from ebay for £1-10/6.

The gauge used was a professional quality gauge "which is suitable for measuring thickness and Corrosion of ships hulls " (manufacturers quote) and has both accuracy and resolution to 0.1mm

 

The report also makes mention that the base plate was NOT blacked.

 

Having seen the corrosion on many baseplates it is beyond me how any thickness meter can ‘accurately’ measure the thickness of the steel. It varies widely even across distances of a few mm on a badly corroded baseplate. 

They do come up with a nice authoritative number though, which people like to see written down. 

[Bee]

I think that the pictures are v. interesting. If all steel structures, sea going ships, oil rigs, bridges and the rest deteriorated at that rate then steel would be dodgy stuff to use.  The fact is that steel in much harsher, salty, and nastier environments lasts for years. I think that we need to see the stuff our boats is made of as needing a lot of care and attention, in fact GRP might be a better material, most of the hire boats on French canals are GRP and they get a proper battering sometimes. In the meantime I shall be dragging our boat out every 3 years and bunging on epoxy paint, none of this shall I shan't I paint the baseplate, if it gets wet it gets painted. Fingers crossed.

[Richard10002]

3 hours ago, Sea Dog said:

The more basic thickness meters can't allow for coatings, etc, to measure just the steel. I suspect this surveyor was using one of those.

Portagauge II ultrasonic..... and he states that it may not differentiate between steel and coating.... 

[Alan de Enfield]

14 minutes ago, Richard10002 said:

Portagauge II ultrasonic..... and he states that it may not differentiate between steel and coating.... 

But there was no 'coating' on the base plate, and it had still grown by 0.9mm (almost 10%).

[MtB]

1 minute ago, Alan de Enfield said:

But there was no 'coating' on the base plate, and it had still grown by 0.9mm (almost 10%).

 

That'll be the rust caked up on each side. 

[cuthound]

According to the attached article production tolerances for 8-15mm steel plate can be up  to +1.4mm, dependent upon class.

 

https://www.bssa.org.uk/topics.php?article=289

[mrsmelly]

21 hours ago, Suki Sjodahl Staples said:

My partner and I are looking to purchase a widebeam and we recently reviewed a survey of one we may be buying. As we are new to boating we want to ensure we aren’t making any mistakes and read in the report that the steel hull has some historic pitting. The deepest one reaches 1.6mm and it states that if it reaches 2mm they will have to be ground out and pad welded over .. I was just wondering if this depth of pitting should be of a big concern or not?

thanks for any help! 

It's not a lot of pitting but if you look as a for instance at my present boats hull built in 2007 it has no measure able pitting, nor did any of my previous boats including some aged thirty years.  Personally I would simply buy one without pitting as they are out there so why buy somebody else's problems? They arnt going to improve with age.

[TheBiscuits]

6 hours ago, Sea Dog said:

The more basic thickness meters can't allow for coatings, etc, to measure just the steel. I suspect this surveyor was using one of those.

The chap who surveyed my boat told me he bought an el-cheapo for about £80 from ebay to test it out against his several £000s one.

 

He came to the conclusion that the best use a decent surveyor has for the cheap one is to hit the hull with it instead of using the hammer, but the hammer is cheaper.

[Alan de Enfield]

9 minutes ago, mrsmelly said:

It's not a lot of pitting but if you look as a for instance at my present boats hull built in 2007 it has no measure able pitting, nor did any of my previous boats including some aged thirty years.  Personally I would simply buy one without pitting as they are out there so why buy somebody else's problems? They arnt going to improve with age.

You are talking sense (amazing !!)

 

My last NB (Reeves 1998) had a 13mm base plate, and, on blacking the hull, was found to be totally corrosion & pitting free, - except a small 'orange tint' at the water line.

(Base plate was not blacked, and appeared never to have been)

 

The 'moor and moor' I think about this corrosion problem the more the evidence seems to be that boats that move a lot are less affected than those that go for a 2-week holiday once a year. Mine had done over 10,000 hours in 15 years.

 

Why buy trouble - it ain't going to 'heal itself'.