In nautical terms, the word sound is used to describe the process of determining the depth of water in a tank or under a ship.
Tanks may be sounded manually or with electronic or mechanical automated equipment.
Per the Code of Federal Regulations, most steel vessels with integral tanks are required to have sounding tubes and reinforcing plates under the tubes which the weight strikes when it reaches the bottom of the tank.
Sounding tubes are steel pipes which lead upwards from the ships' tanks to a place on deck.
Electronic and mechanical automated sounding may be undertaken with a variety of equipment including float level sensors, capacitance sensors, sonar, etc.