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IX. Autopilot Control and Settings
This chapter describes how to control NMEA 2000 (SeaTalk NG) autopilot from the application using
NMEA 0183 protocol.
Modern autopilots have the following modes:
• Standby. In this mode, autopilot is not engaged to the vessel control.
• Auto. The autopilot has a fixed course to steer.
• Wind.
The autopilot steers the boat at a specified angle to the wind.
• Waypoint. The autopilot steers the boat to the specified waypoint.
• Route or Track. The autopilot steer the boat by a specified route.
The difference in the last two modes is that autopilot not only maintains the right direction to the waypoint,
but also tries to follow the line from the previous to the next waypoint.
When NMEA 2000 autopilot is controlled from a NMEA 0183 application, it must receive:
• position of the destination waypoint (from RMB sentence);
• course from the position to the destination waypoint (APB and/or RMB);
• cross track error, means the distance and direction from the current position to the route (APB
and/or RMB and/or XTE).
Depending on the implementation, the NMEA 2000 autopilot can also use the following data (and not
only):
• vessel heading (HDG sentence), but in most systems the heading sensor is connected directly
to the autopilot;
• rate of turn (ROT sentence);
• position, course and speed over ground (RMC sentence).
To control the autopilot, Gateway should receive RMB sentence from the application at least, and APB
and XTE if possible. Gateway also needs to have magnetic variation data, which can be obtained from HDG