Fathometer << fa THOM uh tuhr >> is an instrument used on ships to measure the depth of the water. It sends a pulse or wave of sound down through the water to be echoed back from the bottom. Navigators can measure the depth below the ship by measuring the time it takes the sound to return. Continuous soundings of this kind can be taken throughout a voyage. A fathometer has two main parts: (1) an underwater generator that produces sound and (2) a hydrophone that receives the echo. The echo is amplified and sent to a device called a depth indicator and to a recorder. The reliability of a fathometer depends on a number of factors, such as the depth, temperature, and saltiness of the water. See also Sonar.
