Mechanical Depth Sounder
Mechanical depth sounder, which works like a log, with a spinning impeller measuring depth as it drops through the water column. A release keeps the impeller from turning as the sounder is pulled back up. One gauge measures from 2 to 30 fathoms and the other from 30 to 150 fathoms. Like the patent log, this was also invented by Walker. Patent number 8486 G is engraved on the sounder.