Garmin GSD 28 Advanced Sonar Module

The Garmin GSD 28 is an advanced external sonar module for Garmin GPSMAP 8000 and 9000 series displays, plus listed GPSMAP 7×3, 9×3, and 12×3 units. RapidReturn high-definition sonar, dual-channel CHIRP, and xCHIRP target separation give the module a broad operating range from 25-250kHz. The transducer is not included, so the sounder should be matched to the boat and fishing depth.

Output ranges from 300W to 3kW depending on the selected transducer, giving the installer a wide performance range. Dual low, medium, and high CHIRP channels allow different frequency combinations, while the Garmin network links the GSD 28 to compatible chartplotters. It is not a display, chartplotter, or complete fishfinder package. Power, Ethernet, transducer selection, and network compatibility should be planned together before installation.

Who Is This For?

This Garmin external sonar module suits offshore fishing boats, cruisers, and Garmin glass helm installations that need more sonar capability than a display alone provides. It is not ideal for buyers without a compatible Garmin display or transducer, because the GSD 28 is a module rather than a standalone fishfinder.

Warranty & Support

Garmin provides a 2-year limited warranty. The supplied specifications do not state warranty exclusions or service procedures.

The GSD 28 is the Garmin choice when an existing display needs a serious external sounder rather than a basic internal sonar channel. Its trade-off is the separate transducer and installation work, but the 300W-to-3kW range gives the boat room to grow. Choose it for a planned Garmin network, not as an independent fishfinder.