What is used to create sonar used by boats?

All depth finders, fish finders are in fact sonars. They use a transducer (several styles) mounted in. on, through, the hull. The electronics in the unit sends a signal to the transducer which sends out the sound wave, then becomes a receiver or receive the echo, and send it back to the unit. there the computer interprets that signal and displays the information on the screen.|||I believe the transducers use piezoelectric elements. Typically it is an ultrasonic pulse like 150kHz which is suited to make a narrow beam over short distances (less than a few hundred metres).





Attack sonar on warships uses a lower, audible, frequency and can pick up submarines from several miles away|||It's a sound wave pulse of 50 kHz or 200 kHz which is the newer typical frequency, but there are many others. The higher the frequency, the more detail it can capture, If you were to swim under a boat with the sounder/finder on, you can actually feel the sound pulse. Once beyond 15 feet of depth, you'll no longer feel the pulse, but you can hear the "Snap" of the on/off pulse from the transducer. For lots more details about boating sonar, read the link below.