[Travis C.]

Basically they work like this:

Depthfinders use a signal is cone shaped getting bigger as it travels further from the boat. That signal goes down then bounces off the bottom and returns images within it to the transducer. The size of the signal depends on your cone angle. A bigger angle will mean more coverage but you lose strength. Most have a dual cone (two cone angles you can choose from or its auto).

Think of a flashlight on and hold it out facing down. The flashlight represents your transducer. The circle of light represents your cone angle coverage. As you walk around holding the light anything that pass in the beam would show up on your screen left to right in addition to showing bottom contour/depth.