The GSD 21, is a robust unit designed to operate with stand-alone chartplotters or integrate with the Garmin CANet and Marine Networks. The GSD 21 is a black-box sounder that provides fast Ultrascroll displays and 500-watt (RMS) sounder capability to 2000 series and 292/392/492 series chartplotters featuring the Garmin CANet bus. The GSD 21 will work with a serial connection to other Garmin plotters without the CANet connection, but will not offer Ultrascroll capability. The unit's all-new, high-dynamic range analog sonar receiver provides exceptional performance in water as shallow as one foot on down to depths of 1,500 feet. It connects to a dual frequency transducer (50/200 kHz) for deep-water performance or a single frequency, dual beam width transducer (narrow/wide) for operation in shallow freshwater as well as deeper water. Provides 500 W transmit power with dual frequency transducer or 400 W with dual beam width transducer.