Thank you for your tips guys.
It seems to me that the problem is on the autopilot side, since I can see that the
current BTW - Bearing to waypoint updates with the one shown on the chart plotter. If the autopilot steered this course (or heading), it would at least hit the next waypoint. Unfortunately it does not correct its bearing until it is way out of course. I guess it should also try to minimize the XTE, in other words try to stay on the course line. It seems to do this, but not until the XTE is 0.04-0.05 NM or higher.
I have tried adjusting the gain on the autopilot, but it did not help.
When it comes to the NMEA connection, the pins 5 (ground) and 3 (data out) from the RS-232 port is connected to the NMEA IN connections on the Smartpilot Controller (not the S2
head unit). It tells me the
current BTW, so I guess the connection is working. My
logs of the NMEA data sent to the autopilot looks like this:
$INRTE,1,1,w,MyRoute,WP2,WP3
$INWPL,6417.450,N,01000.180,E,WP2
$INWPL,6417.410,N,01000.250,E,WP3
$INAPB,A,A,0.001,L,N,A,V,60.075,T,WP2,59.189,T,60. 075,T
$INAPB,A,A,0.004,L,N,V,V,60.075,T,WP2,56.553,T,60. 075,T
$INAPB,A,A,0.007,L,N,V,V,60.075,T,WP2,52.617,T,60. 075,T
$INAPB,A,A,0.010,L,N,V,V,60.075,T,WP2,47.806,T,60. 075,T
$INAPB,A,A,0.013,L,N,V,V,60.075,T,WP2,41.923,T,60. 075,T
$INAPB,A,A,0.016,L,N,V,V,60.075,T,WP2,34.705,T,257 .292,T
Googling the APB NMEA sentence, it is to be understood like this:
Field Number:
1) Status
V = LORAN-C Blink or SNR warning
V = general warning flag or other
navigation systems when a reliable
fix is not available
2) Status
V = Loran-C Cycle Lock warning flag
A = OK or not used
3) Cross Track Error Magnitude
4) Direction to steer, L or R
5) Cross Track Units, N = Nautical Miles
6) Status
A = Arrival Circle Entered
7) Status
A = Perpendicular passed at waypoint
8) Bearing origin to
destination
9) M = Magnetic, T = True
10)
Destination Waypoint ID
11) Bearing, present position to Destination
12) M = Magnetic, T = True
13) Heading to steer to destination waypoint
14) M = Magnetic, T = True
15) Checksum
Anders.