Echo sounders vs. sonar

​An echo sounder, a.k.a. fish finder or depth sounder, let's you view the seabed currently under the vessel utilizing a fixed mount transducer. A sonar enables you view the waters forward, port, starboard or aft of the vessel utilizing a hoist operated transducer element which scans 360 degrees. The sonar user also has the ability to adjust the tilt of the transducer element.
 
Note that some manufacturers use the term "Sonar" when referring to a fixed mount transducer application.