Under way the water moves past, the bottom drops away, and a spot found at nine is lost by noon. What matters: readings that hold at trolling speed, coverage in deeper water, GPS-tagged mapping, and a way to mount or tow the sonar. Anything listed here answers at least one of these demands.

On the ice you fish one small hole, watch a jig ten feet below, and lose battery to the cold. A flasher-style live display, cold-weather runtime, a beam that reads through an augered hole, and enough detail to see a fish approach are what count. Every option below covers at least one of these needs.

A kayak gives you no power supply, no console, inches of deck, and water on every side. A self-contained battery, a size that fits between rods and paddle, operation with one hand, and a body that floats if it goes over are what count. Qualifying for this page takes at least one of these strengths.

From a bank there is no transducer mount and no way to the drop-off except a cast. What counts: something castable on line, depth mapping built by reeling in, a phone as the screen, and wireless range that survives a long throw. Products below earn a spot on at least one of these fronts.