2.7 mm steel plate thickness

[Tomek]

Hi. I've just had a steel coastal cruiser surveyed. As it is 1968 construction it was build with 1/8" plate. Now the thickness is between 2.7 mm to 3 mm. The surveyor says it is acceptable measurement and no overplating is needed. I though the original 3 mm isint that much but 2.7?! Can anyone please advise if it is safe? Thanks! 

[TheBiscuits]

1 minute ago, Tomek said:

Hi. I've just had a steel coastal cruiser surveyed. As it is 1968 construction it was build with 1/8" plate. Now the thickness is between 2.7 mm to 3 mm. The surveyor says it is acceptable measurement and no overplating is needed. I though the original 3 mm isint that much but 2.7?! Can anyone please advise if it is safe? Thanks! 

You could always ask another surveyor if you don't believe the one you have just paid.

[Alan de Enfield]

No problem - it won't leak until it gets down to 0.0mm.

 

Your only problem MAY be that some insurance companies are refusing to insure at less than 4mm, so you may need to call around.

 

If it has only lost about 0.5mm in 50 years, why would you think that it is going to sink in less than another 200+years. ?

Edited August 4, 2018 by Alan de Enfield

[Tomek]

Just now, TheBiscuits said:

You could always ask another surveyor if you don't believe the one you have just paid.

The survey was done for insurance purposes so I believe him when he says it's acceptable and insurer will take the risk. Question is whether I should take the risk too...

[rusty69]

Lost 0.5mm in 50 years, probably last a bit longer 

Edited August 4, 2018 by rusty69

[ditchcrawler]

1 minute ago, Tomek said:

The survey was done for insurance purposes so I believe him when he says it's acceptable and insurer will take the risk. Question is whether I should take the risk too...

so its lost 0.3 mm in 50 years

[Alan de Enfield]

Just now, ditchcrawler said:

so its lost 0.3 mm in 50 years

No - 1/8" is  3.175 so its lost 0.475 in 50 years.

[ditchcrawler]

1 minute ago, Alan de Enfield said:

No - 1/8" is  3.175 so its lost 0.475 in 50 years.

So if it continues at this rate how long before it sinks

[Tomek]

6 minutes ago, ditchcrawler said:

so its lost 0.3 mm in 50 years

My worry is more mavigating on tidal and coastal waters or going aground while on river/canal.

[Alan de Enfield]

5 minutes ago, ditchcrawler said:

So if it continues at this rate how long before it sinks

See post #3

[MtB]

12 minutes ago, Tomek said:

The survey was done for insurance purposes so I believe him when he says it's acceptable and insurer will take the risk. Question is whether I should take the risk too...

 

 

What risk is that then?

 

(I can't think of any!)

 

 

 

[Alan de Enfield]

4 minutes ago, Mike the Boilerman said:

 

 

What risk is that then?

 

(I can't think of any!)

 

 

 

Shopping Trolley ?

Rocks (after lock approach repairs) ?

Widebeams ?

Hirers ?

C&RT maintenance standards ?

[Captain Pegg]

17 minutes ago, Alan de Enfield said:

No - 1/8" is  3.175 so its lost 0.475 in 50 years.

You can't be that precise. You only know the nominal plate thickness not the actual thickness and the applicable tolerances could put a significant level of variance into the small numbers we are dealing with here. Then factor in the accuracy of the ultrasonic test reading.

 

If the OP wasn't worried about the boat before the survey then they should be no more worried afterwards, and probably less so.

 

JP

Edited August 4, 2018 by Captain Pegg

[TheBiscuits]

1 minute ago, Alan de Enfield said:

C&RT maintenance standards ?

Well at least someone is hitting the standards. 

 

[Alan de Enfield]

1 minute ago, Captain Pegg said:

Then factor in the accuracy of the ultrasonic test reading.

Very true - the surveyor may have missed that small area at 0.001mm which is ready to 'burst open' the next time the engine is started.

[rusty69]

3 minutes ago, Alan de Enfield said:

Shopping Trolley ?

Rocks (after lock approach repairs) ?

Widebeams ?

Hirers ?

C&RT maintenance standards ?

Mattresses! 

 

Oh hang on, they're soft. 

[Captain Pegg]

3 minutes ago, Alan de Enfield said:

Very true - the surveyor may have missed that small area at 0.001mm which is ready to 'burst open' the next time the engine is started.

You can never test absolutely every square millimetre of the hull for pits but the failure mechanism will be a small leak not anything sudden and dramatic like you imply. It will probably be noticed before anything major happens if the boat is occupied or the boat may sink in a few feet of water on it's mooring if it's unattended. Not pleasant but no-one will die and it will be insured against losses. There are far bigger risks on the average inland waterways boat than an old or thin steel hull.

 

JP

[Alan de Enfield]

1 minute ago, Captain Pegg said:

There are far bigger risks on the average inland waterways boat than an old or thin steel hull.

Agreed and the OP should take note.

[Tomek]

Thanks guys. I'll consider all your opinions for sure

[MtB]

11 minutes ago, Captain Pegg said:

There are far bigger risks on the average inland waterways boat than an old or thin steel hull.

 

Good thing the OP presumably won't be cruising the inland waterways then isn't it!

 

 

50 minutes ago, Tomek said:

coastal cruiser

 

[Alan de Enfield]

2 minutes ago, Mike the Boilerman said:

 

Good thing the OP presumably won't be cruising the inland waterways then isn't it!

 

 

 

You've done it again - read the thread from the top - stop at post #9

[Captain Pegg]

3 minutes ago, Mike the Boilerman said:

 

Good thing the OP presumably won't be cruising the inland waterways then isn't it!

 

 

 

Oh yeah. But 99% of the folk reading this will be inland waterways folk, must cater for them rather than the 1% that have been barred from YBW. 

 

JP

[MtB]

5 minutes ago, Alan de Enfield said:

You've done it again - read the thread from the top - stop at post #9

 

 

Sorry. I forgot about the unwritten posting rule that everyone here instinctively obeys. The one that says we must not read the thread first, in case we post something pertinent to the facts  

[Momac]

 

The thickness  tolerance on the original plate depends on the grade of plate and according to present day standards may be in the order of +/- 0.4mm and possibly greater so a thickness of 2.7mm  could easily  be within the original tolerance.

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

 

If it's a sea  boat is it  painted inside and out ?

Are you certain it was built with 1/8th inch plate  and not something thicker ? 

 

 

[Neil2]

Bear in mind that sea going boats are generally built as light as practicable  - to be faster, more efficient, greater payload etc. but they also tend to be better protected against rust.  The plating can be as thin as you like if you don't let rust get a hold.  OTOH narrrowboats have to be inherently heavy to pull them down in the water as they are basically just a steel box so there's no real incentive to use "thin" plate unless it's on cost grounds and a jumbo baseplate can avoid the need for ballast - even more internal space.  The use of thick plating has created the tendency to associate thicker plating with better corrosion resistance, which is true up to a point, but it doesn't mean a boat built with 1/8 plate or even 1/16 is unsafe, so long as the hull is protected and maintained.