All Class B and Class B+ AIS transponders can transmit the True Heading of the vessel as part of the dynamic data they transmit to other vessels; MMSI Number, Position, COG, SOG, etc. If received most charting systems will plot the AIS target with both the COG and True Heading vector displayed, useful when the vessel is stationary and COG becomes unstable/inaccurate.
Our AIT2500 and AIT5000 units can receive the True Heading (HDT or THS sentences) data via their Low Speed NMEA 0183 Input (Yellow+ and Green- wires) or via PGN#127250 Vessel Heading on NMEA 2000.
However, not all NMEA 2000 systems will transmit True Heading and in some cases they transmit a wrong value or just a fixed 000º. This results in the AIS target being plotted with a very strange heading vector or the boat appearing to be moving side-ways or backwards.
If this happens and you cannot correct or suppress the True Heading value on the NMEA 2000 network, then you can stop the AIT2500/AIT5000 from receiving True Heading over NMEA 2000, by following the procedure below….
Using the proAIS2 software, go to the Serial Data tab and then copy and paste the following commands in to the box at the bottom of the page and click the “Send” button (see image below).
- To stop reception of True Heading data over NMEA 2000 send this command:
$PSMT,0,3,0x2C75B2FA,1,n2kignss 0,0*13 - To enable it again send this command:
$PSMT,0,3,0x2C75B2FA,1,n2kignss 1,0*12
….if the command was successfully received and actioned, you should see Transponder respond with…
- $PSMT,255……….etc. (basically, the same as the command but 255 instead of 0 after the $PSMT, text)