Depth sounder and Fathometer

Fathometer and depth sounder are semantically related in sonar topic. In some cases you can use "Fathometer" instead a noun phrase "Depth sounder", when it comes to topics like echo sounder.

Fathometer noun - Depth finder for determining depth of water or a submerged object by means of ultrasound waves.

Depth sounder and fathometer are semantically related in sonar topic. You can use "Depth sounder" instead a noun "Fathometer", if it concerns topics such as echo sounder.