Jump to content

Testing the welding integrity of an overplated boat


Bloomsberry
 Share

Featured Posts

A hull insurance survey on my overplated boat a few years ago revealed that some of the welds of the overplating were 'undercut' and needed re-welding. Surveyor wanted the cavity of the overplating pressurised after the work to test it's integrity. However, the boatyard doing the work recommended against this as it risked damaging the overplating. In the end the work was done without pressurising and opted for 3rd party insurance instead as the boat is  quite old now anyway.

 

So I was wondering the best method of checking the integrity of the cavity which obviously means penetrating the overplating from either the outside or within the boat. In the end I decided to drill a small hole from the inside of the boat to the cavity whilst the boat was in the water which would show if there was a leak from the outside. I was ready to quickly tap the hole if water was present and plug up using a countersunk pin.

 

There are 6 main areas of overplating on the boat so located a point inside the boat for each , below the waterline and drilled a small hole in each. I put some tape on the drill to give me an idea when the drill had passed through the hull itself. I was half expecting there to be some breach in the welds but as it happened each cavity was completly dry with no water at all which I was relieved at. So I tapped each hole and put a countersunk pin in each that can be readily removed when testing the integrity again, probably prior to taking the boat out for blacking so any breach can be addressed also.

 

Has anyone else done this to their overplated boat ?

 

Link to comment
Share on other sites

13 minutes ago, Bloomsberry said:

A hull insurance survey on my overplated boat a few years ago revealed that some of the welds of the overplating were 'undercut' and needed re-welding. Surveyor wanted the cavity of the overplating pressurised after the work to test it's integrity. However, the boatyard doing the work recommended against this as it risked damaging the overplating. In the end the work was done without pressurising and opted for 3rd party insurance instead as the boat is  quite old now anyway.

 

So I was wondering the best method of checking the integrity of the cavity which obviously means penetrating the overplating from either the outside or within the boat. In the end I decided to drill a small hole from the inside of the boat to the cavity whilst the boat was in the water which would show if there was a leak from the outside. I was ready to quickly tap the hole if water was present and plug up using a countersunk pin.

 

There are 6 main areas of overplating on the boat so located a point inside the boat for each , below the waterline and drilled a small hole in each. I put some tape on the drill to give me an idea when the drill had passed through the hull itself. I was half expecting there to be some breach in the welds but as it happened each cavity was completly dry with no water at all which I was relieved at. So I tapped each hole and put a countersunk pin in each that can be readily removed when testing the integrity again, probably prior to taking the boat out for blacking so any breach can be addressed also.

 

Has anyone else done this to their overplated boat ?

 

But what about if the old plating is actually porous which is possible if the boat leaked and required over plating, you would never get a pressure test between the two 

  • Greenie 1
Link to comment
Share on other sites

As the owner of a forty year old boat,I find this topic quite interesting. Although my insurance survey was ok, I am quite prepared for bad news every couple of years when it is out of the water for blacking.

Surely if a boat is overplated,then it will take 10,20,or even 30psi between the overplating and the old hull without damage.

If as the OP has done from the inside,you will be able to see if there is a water leak from the overplating.

If the hull won't hold pressure,then you either leave as is and monitor the situation with the countersunk pins [whatever they are] I would have  tapped them and inserted a screw sealed with gasket cement,or strip the trim out to find the air leak and seal either with spot welding or a fibreglass patch.

I wonder why the boatyard recommended not pressure testing the overplating? Were they unsure of the quality of their welding?

Link to comment
Share on other sites

12 minutes ago, Mad Harold said:

As the owner of a forty year old boat,I find this topic quite interesting. Although my insurance survey was ok, I am quite prepared for bad news every couple of years when it is out of the water for blacking.

Surely if a boat is overplated,then it will take 10,20,or even 30psi between the overplating and the old hull without damage.

If as the OP has done from the inside,you will be able to see if there is a water leak from the overplating.

If the hull won't hold pressure,then you either leave as is and monitor the situation with the countersunk pins [whatever they are] I would have  tapped them and inserted a screw sealed with gasket cement,or strip the trim out to find the air leak and seal either with spot welding or a fibreglass patch.

I wonder why the boatyard recommended not pressure testing the overplating? Were they unsure of the quality of their welding?

so 30psi in a patch say a yard square is a little over 17 tons

Link to comment
Share on other sites

5 minutes ago, Mike the Boilerman said:

If the pressure tests are successful this indicates the overplating wasn't necessary in the first place, other than to satisfy some bod behind a desk at the insuranc company.

Does it,or does it suggest an acceptable standard was achieved in the repair job?

Link to comment
Share on other sites

Just now, ditchcrawler said:

so 30psi in a patch say a yard square is a little over 17 tons

No,eight and a half tons. The air is pushing both ways.It would not be necessary to pressure test a patch that small,

I agree with MtB about unnecessary overplating.I have expressed my opinion before that many boats are overplated to satisfy insurance companies,and overcautious surveyors.

Link to comment
Share on other sites

4 minutes ago, Mike the Boilerman said:

 

Yes, usually about another 40 years.

 

A 8mm hull us may usually seems to take 40 years to get down to the 4mm at which surveyors declare "FAIL, OVERPLATE URGENTLY".

 

So another 40 years to penetrate right through. 

Phew. Ours may need overplating in a few years according to the surveyor, but as I won't want it after 40 years, probably wont bother. Thanks

Link to comment
Share on other sites

24 minutes ago, Mad Harold said:

No,eight and a half tons. The air is pushing both ways.

No. It's pushing in all directions. So you need to divide by infinity not by two. Then you'll find that logically there's no pressure on any surface at all.

 

:blink:

 

I love bad Physics. You can prove anything you want.

 

JP

Edited by Captain Pegg
Link to comment
Share on other sites

1 hour ago, Mad Harold said:

No,eight and a half tons. The air is pushing both ways.It would not be necessary to pressure test a patch that small,

I agree with MtB about unnecessary overplating.I have expressed my opinion before that many boats are overplated to satisfy insurance companies,and overcautious surveyors.

So if its 8.5 in each direction what is that on the weld

 

Link to comment
Share on other sites

1 hour ago, ditchcrawler said:

so 30psi in a patch say a yard square is a little over 17 tons

Correct. Actually 30 psi would load the plate at 21 tonnes per sq.m. Plenty enough to wreck your boat.

That would be 21 t/m2 on both the overplate and on the original hull. (each force has an equal and opposite reaction remember)

Inspecting for water leakage would not give the full story either. The weld metal could be paper thin and still be watertight.

The only way to prove the welds would be to inspect them by dye pen or X-ray - both expensive as the weld has to be dry and clean.

I suggest the only practical method is a close visual inspection by an expert surveyor.

You say the welds are undercut. That is poor quality welding and they should be ground out and re welded. There is no point in having, say, 6mm plate if the weld is only 3mm thick.

Edited by yabasayo
Link to comment
Share on other sites

Thanks for the replies

 

My main concern was the possibility of there being water in the cavity between the overplate and the hull, which would cause corrosion on the unprotected surfaces which would slowley get worse over time.

 

As long as the cavity is dry then all is good (for now).

 

Also, having the ability to check if there's water between the hull and overplate in the future is a re-assurance and if this is done prior to docking for blacking then arrangements can be made to repair if there are any breachs.

Edited by Bloomsberry
Link to comment
Share on other sites

6 minutes ago, Bloomsberry said:

Thanks for the replies

 

My main concern was the possibility of there being water in the cavity between the overplate and the hull, which would cause corrosion on the unprotected surfaces which would slowley get worse over time.

 

As long as the cavity is dry then all is good (for now).

 

Also, having the ability to check if there's water between the hull and overplate in the future is a re-assurance and if this is done prior to docking for blacking then arrangements can be made to repair if there are any breachs.

But can corrosion take place without oxygen, which I would imagine wouldn’t be present between the plates?

Link to comment
Share on other sites

15 minutes ago, Bloomsberry said:

Thanks for the replies

 

My main concern was the possibility of there being water in the cavity between the overplate and the hull, which would cause corrosion on the unprotected surfaces which would slowley get worse over time.

 

As long as the cavity is dry then all is good (for now).

 

Also, having the ability to check if there's water between the hull and overplate in the future is a re-assurance and if this is done prior to docking for blacking then arrangements can be made to repair if there are any breachs.

Wouldn't you see damp patches as the hull dried if water can get in and out

Link to comment
Share on other sites

Create an account or sign in to comment

You need to be a member in order to leave a comment

Create an account

Sign up for a new account in our community. It's easy!

Register a new account

Sign in

Already have an account? Sign in here.

Sign In Now
 Share

  • Recently Browsing   0 members

    No registered users viewing this page.

×
×
  • Create New...

Important Information

We have placed cookies on your device to help make this website better. You can adjust your cookie settings, otherwise we'll assume you're okay to continue.