Display of a consumer type fishfinder

Fishfinder – an instrument used to locate fish underwater by detecting reflected pulses of sound energy, using SONAR technology. A modern fishfinder displays measurements of reflected sound on a graphical display to locate schools of fish, underwater debris, and the bottom of body of water. Fishfinder instruments are used both by sport and commercial fishermen. Modern electronics allows a high degree of integration between the fishfinder system, marine radar, compass and GPS navigation systems.

Sonar – (originally an acronym for SOund Navigation And Ranging) is a technique that uses sound propagation (usually underwater, as in submarine navigation) to navigate, communicate with or detect objects on or under the surface of the water, such as other vessels. Two types of technology share the name “sonar”

  • passive sonar is essentially listening for the sound made by vessels
  • active sonar is emitting pulses of sounds and listening for echoes.

Sonar may be used as a means of acoustic location and of measurement of the echo characteristics of “targets” in the water.


  • recreation
  • commercial fishing
  • fisheries management


  • drones – Glider Paloosa
  • transmitters

New and improved

  • FishHunter Sonar a bobber, floating around the water, uses a smartphone to show where the fish are.

That’s engineering

  • Hydroacoustics – an electrical impulse from a transmitter is converted into a sound wave by an underwater transducer, called a hydrophone, and sent into the water. When the wave strikes something such as a fish, it is reflected back and displays size, composition, and shape of the object. The exact extent of what can be discerned depends on the frequency and power of the pulse transmitted. Knowing that the speed of the wave in the water is 4921 ft/s (1500 m/s) in seawater, 4800 ft/s (1463 m/s) in freshwater (typical values used by commercial fish finders), the distance to the object that reflected the wave can be determined.

Engineering ideas

  • hydroacoustics, SONAR, sound energy, reflection, marine radar, compass, GPS navigation systems

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