I always start my surveys on metal boats by using Thermal Imaging of the hull. This helps me locate the structural components of the metal boat. I am also looking for trapped moisture and/or water. If this is found, then there is a good chance there will be corrosion. Next I conduct an inspection of the bilge of the boat, including, anchor, sail, cockpit lockers, and lazarettes. Now I have a very good idea where to concentrate my UTM-audio gauge. I take readings of the whole hull, but will do more readings in the areas of concern.
When I see water in a bilge of a metal boat beyond what might be in a sump I get concerned. I would like to see dry bilges on all metal boats, but this is not always possible. On Tuesday I surveyed a steel trawler. Overall this boat looked to be in fair condition, but then I saw the water in the bilge, a lot of it! There was heavy scale in some areas because of the standing water. I knew this was an area I needed to spend some time getting thickness readings.
The next day I did my audio gauge. My readings indicated plate wastage. In some areas I could not get a reading that most likely is caused by heavy scale. My visual inspection from inside confirmed the heavy scale. When I arrived at the boat I noticed some weeping from what I hoped was paint blisters. Then an hour later water stared streaming from one of the blisters. Just to think only the paint was holding this section of plate together.
The good news! The boat was out of the water it will not sink. Steel boats can fixed; by cropping out the bad plate and adding new. In a short period of time, she will be underway again.
The moral of this story? If you own a metal boat keep an eye on the bilges.
I will post some photos next.