3100 SERIES SAILING INSTRUMENTS. Navman's new generation of instruments are the cutting edge of digital marine technology: they feature the advanced NavBus system, which allows complete freedom to build the system you want by using any combination of displays with only one set of transducers. Visibility is fantastic with up to 38mm backlit digits and nighttime use is easy with amber lighting and backlit keys. The 3100 series instruments are extremely simple to use and to connect. They now offer greater flexibility to meet your boating needs. DEPTH: This very powerful depth sounder features giant digits for easy reading and peace of mind. NavBus System allows depth repetition throughout the boat. . Displays to 400 feet, 130 meters or 67 fathoms. Too deep and too shallow alarms, External alarm option (visual or audible).