— 32 —
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 APB and RMB sentences from
the application. Gateway also needs to have magnetic variation data, which
can be obtained from HDG or RMC sentences or from the NMEA 2000 messages
(must be turned on in the Gateway settings).
If your NMEA 2000 network has GPS data, it can use data already available
on NMEA 2000 and sending of the ROT, HDG and RMC sentences from
the application may not be required. It is better to send minimal data from a PC
to the NMEA 2000 network if possible.
Depending on the autopilot sensitivity settings, autopilot can control your vessel
smoothly or aggressively. The application only provides the situation (where
is the waypoint and how far we are from the route), but the course to steer
and the rudder angle are defined by the autopilot logic.
Switching of waypoints is the work of the application. If the arrival radius is set
to 1 NM, application can switch to the next waypoint when the current point
is still a mile away. If your route is circular or approximately so, the application can
unexpectedly switch from the first point to the last. You should be familiar with your
