Audio Gauging ?

Moisture readings?

AND Wet.

On metal boats it is a procedure that you use to measure the hull plate thickness. You typically know the original thickness from the build and as you go around the vessel you compare to see if you have have had plate corrosion or deterioration. For boats that are in class it is required at 5 year special survey intervals and if a certain percentage loss vs original thickness is found you need to replace that section of plating(this can be a very involved repair depending on the location, original construction method, and a number of other factors). Taking the reading is done with a special meter and by trained personnel. Then the readings are typically translated into a spread sheet format which is presented to your class surveyor and also kept on board for future reference.

Here is a picture of one repair from a recent yard period I did on a 30 year old steel hulled boat.

Hope this helps.

Interesting subject. Hope there are more comments and pics on repairing metal hulls. Have read many times they are not as difficult repair as some think. What the pics shows looks fairly simple.

Still look like moisture readings to me.

The proper way to repair thinning or damaged plating is to cut it out as in the picture on post #4. An easier, cheaper and sometimes acceptable repair is by plating over the area which is called a "doubler." Doublers are not class approved but for the steel yachts not concerned with class, it makes some fixes simple. There's something more comfortable about cutting and repairing a steel hull versus fiberglass.

Yes, the metal patch is probably much stronger than a fiberglass patch. Doubler could also be a quick fix until back at homeport.