Audio gauge meter testing of a steel hulled houseboat. 4.4 mm is 0.1732283 inches. Many steel boat builders are using 1/8th inch (0.125) material.

Audio gauge meter testing of a steel hulled houseboat. 3.9 mm is 0.1535433 inches. Many steel boat builders are using 1/8th inch (0.125) material.

Thermal imaging shows this bottom is uniform in thickness. There isn't a lot of temperature difference showing.

This image shows an Outdrive that did not have protection against stray electrical currents. The white spots are either pitting that actually goes completely through the metal or is thin enough that it will do so soon.