non-destructive testing equipment

Does anyone know of some device (other than a drill bit) that can tell me the depth of the fairing compound on an aluminum hull? My company was recently given the job of completing an aluminum yacht. The fairing and primer are already on the hull but we've found a few spots where the mud is way too thick.

We would like to non-destructively survey the rest of the hull and find if these are isolated incidents or if the fairing crews were consistently heavy handed. But our searches for a suitable gizmo have been fruitless.

If you know of an instrument like this, or have used another method of dealing with a situation like this, I would appreciate your advice.

thanks,
That Guy
you know, the one that works for that boat company ;)

[fishboat]

Try

http://www.bykgardner.com/html/byk/index.html

We use their equipment to check paint coating thickness on steel panels. Non-ferrous testing might be more difficult, call them & see what they say. Their equipment isn't cheap, but what is?

Thank you fishboat for the link to BYK-Gardner. We have considered coating testers like those in B-G's catalog but the problem is the depths involved. Skimming through their catalog I saw instrument ranges from 0-20mil, and up to 700mil.

The chunk of mud that came off the hull - and that raised our curiosity - is 4 inches thick. Yup, a _four_inch_thick_ layer of fairing compound between the metal hull and the first primer coat. I recently heard that we're grinding down the mud; re-shaping the non-structural hull and trying to get its outer surface closer to the metal hull, so now my original question has become academic

But is a topic that we kick around for fun now and then. One guy thinks he can adapt a fish finder to the purpose while I think an electromagnet on the inboard side and a ferrous deflection meter on the outboard side (calibrated against known samples) would answer our question.

Or maybe the real answer is to give the fairing crew a set amount of mud and pay them a bonus for each pound of it left in the buckets after the hull is fair.

[sailvayu]

Maybe that bonus should go to the folks building the hull in the first place

an ultrasonic thickness gage should work to measure that material up to 4" thick. One company that makes them is GE Panametrics.

Did I read that right , 4" thick , sound's more like redesigning the hull vs fairing . Having built a few of these thing's , I would sweat bullet's over a quater of an inch . I dont suppose you would name the builder or design ?? would ya ?? .
You could use two plumbs bob's , and drop them to the ground , while taking some measurement's from the inside , then measure between the " bob's " , do this on station's , as a rough guide or pay a company to come out and take some shot's .
Better yet run , what ever you do , might just come back to bite you !! .