Equipment Needed to Display Opposite Tack Heading on a GMI 10 or GMI 20

The opposite tack reading requires data from three pieces of equipment a wind, water speed, and heading sensor. Without data from all three pieces of equipment, the chartplotter cannot accurately calculate the opposite tack. 

Garmin makes the GST 43 thru-hull transducer that provides water speed, temperature, or an Airmar 810 will provide depth, speed, and temperature. If the vessel has an autopilot installed, the course computer provides heading information; otherwise, Garmin has a 9-axis Heading Sensor or a third-party heading sensor connected via NMEA 2000 that provides the heading reading required for the opposite tack reading