If you are serious about fishing and going deep you need this sonar module. It can take dual frequency 1kW transducers as well as being able to plug in DownVu and SideVu transducers. Generally matched up with the GPSMAP 8400xsv series chartplotters it will start losing the bottom on low CHIRP at 1200m on a 1kW transducer. It dramatically improves target separation and clarity at different depths and gives you much clearer picture of what's under the boat. Get the most out of your transducers by boosting them with the GSD25 Sonar Module