Use in Freshwater and Saltwater Garmin Fishfinder 400C is available with a choice of dual beam or dual frequency transducers, so itâ s readily adaptable for both freshwater and saltwater fishing. The 400 watt ( RMS) dual beam version offers a wide fish-finding cone and reaches depths of 900 feet. With the 500 watt ( RMS) dual frequency transducer, you can reach a depth of 1, 500 feet. Connect with CANet® Fishfinder 400C features a crisp, ultra-bright 4â QVGA color display, plus UltraScroll⢠for screen updates at live-action speeds. It' s also CANet-compatible, so you can share sonar information with plotters located elsewhere in your boat.