Ultrasonic metal thickness detector

[BODs SR2]

Could anyone recommend one of these for diy use. Got a 1976 hull and although I’ve had a professional survey done I would like to check out a few specific areas next time it’s out the water for blacking. 

[Tracy D'arth]

Some better than others. No cheap ones will allow anything like an accurate reading unless you grind back to clean metal. I would buy the cheapest and try it out on clean plate that you know the thickness off to see how accurate it is.

[BODs SR2]

I can imagine you get what you pay for. Getting the professionals in is £250+ so something to play with there. If I calibrate on a known then get down to the bare metal it should give me an idea if further investigations are needed. Also it’s there to use again. From my experience with surveyors they have an agenda and are reluctant to work with you and spend time on any concerns you might have. 

[harrybsmith]

I have a cheap one (bought 2nd hand), for the first 10 or so measurements after calibration it's dead accurate, after that some measurement drift creeps in and it needs recalibration. A hammer can also be used as a thickness sounder (used extensively in industry, I did a lot of it in my last job), learn what good, thick metal sounds like when hit and you'll soon hear the difference on a thin bit

[blackrose]

1 hour ago, Tracy D'arth said:

Some better than others. No cheap ones will allow anything like an accurate reading unless you grind back to clean metal. I would buy the cheapest and try it out on clean plate that you know the thickness off to see how accurate it is.

 

That's probably a good idea. Buy one from Amazon and test it on some clean plate of a known thickness or against Vernier measurements. If it's no good you can easily return it. Just keep doing that until you find a decent one. 

 

I'd be interested to see what you find so please report back on what model you end up with and how it performs.

 

9 minutes ago, harrybsmith said:

I have a cheap one (bought 2nd hand), for the first 10 or so measurements after calibration it's dead accurate, after that some measurement drift creeps in and it needs recalibration. 

 

Do you use it in conjunction with some water based gel to get a proper contact, or has the technology moved on now and you don't need the gel?

Edited April 8, 2023 by blackrose

[David Mack]

My eBay cheapie (£80 about 18 months ago) came with a metal disc to check the calibration from time to time.

I used hand soap in a pump dispenser as a contact gel. Cheap, easy to use and can be washed off.

[harrybsmith]

45 minutes ago, blackrose said:

 

Do you use it in conjunction with some water based gel to get a proper contact, or has the technology moved on now and you don't need the gel?

 

Yes I do use gel, and yes it is necessary 

 

Accuracy verified as I've been chopping lumps out my boat so can caliper the thickness of them when removed 

[ditchcrawler]

5 hours ago, David Mack said:

My eBay cheapie (£80 about 18 months ago) came with a metal disc to check the calibration from time to time.

I used hand soap in a pump dispenser as a contact gel. Cheap, easy to use and can be washed off.

What effect does crud on the other side of the steel have on measurements, ie. the inside of the hull?

[David Mack]

I can't tell how accurate it is in an absolute sense, but it certainly showed thin areas, which I could confirm looking from the inside in accessible areas.

[Phoenix_V]

they all work on nice new clean steel, the issue is how well they work when there is a load of rust on the other side !

[David Mack]

To be fair I was using mine from the outside which had been grit blasted and had one coat of 2 pack epoxy primer, which gave a good surface for contact Worked fine on flatish areas but I couldn't check areas of significant pitting.

[john.k]

I used to get a boiler inspector in for yearly inspections,and would assume he had a lab standard instrument.....and he required all contact surfaces to be  bare metal for  ultrasonic measurement,and used the gel..............so its not any indicator of an inferior instrument............dirt ,scale ,rust or paint show clearly as multiple layers ............however ,a boat is actually inside out ......you should test from the (hopefully) clean inside surface of the hull.

Edited April 9, 2023 by john.k

[blackrose]

7 hours ago, john.k said:

 ............however ,a boat is actually inside out ......you should test from the (hopefully) clean inside surface of the hull.

 

The OP was talking about testing his hull in a few specific areas next time it's out the water. I assumed that meant taking measurements from the outside.

[BODs SR2]

I’ll opt for trying ones off Amazon for now. Keep you posted. 

[ditchcrawler]

6 hours ago, blackrose said:

 

The OP was talking about testing his hull in a few specific areas next time it's out the water. I assumed that meant taking measurements from the outside.

Well it does save lifting floors and removing ballast and removing linings and spray foam insulation  doing it from outside 

[BODs SR2]

Apparently how these detectors work is they reflect against a different substrate so bare the metal on the outside and as soon as the wave hits paint rust etc it will reflect back.