We had an enquiry today from a US Dealer about why some chart plotters do not display all of the 26 different AIS Messages that are transmitted by Ships, AtoNs, AIS MOB systems and other AIS equipment. This is quite a complex issue as there are three variables at play….
1) The AIS transponder or Receiver
Most AIS receivers and transponders support all AIS messages, however it is true that early Class A and some receiver only units do not support all AIS messages. It is always best for the owner of older AIS units to check that they have the latest firmware in their units and to even contact the manufacturer to see if their unit supports the more recent AIS messages like AtoNs and AIS SARTs (MOB) systems.
The good news for Digital Yacht customers is that every AIS unit we have ever sold supports all of the 26 AIS messages currently defined.
2) The Chart Plotter or Software Application
Even if the AIS transponder or receiver is compatible with all 26 messages, it does not necessarily mean that the chart plotter or software application (running on PC, iPad, etc.) knows how to read and display the AIS messages.
When AIS was first released, many manufacturers and software developers just did a partial AIS implementation, only supporting what they considered to be the most important AIS messages. Also due to delays in the definition of Class B transponder messages, some of the manufacturers only supported the display of Class B targets but not the reading of the Class B static data (boat name, boat type, etc.). Even large manufacturers like Raymarine, Navico and Garmin took a few years to release new firmware for their plotters to improve the number of AIS messages that they supported.
3) NMEA2000 PGNs for AIS
Due to delays in the NMEA committee defining PGNs for AIS, some plotters only support some of the 26 AIS messages when connected via NMEA2000, even if they support all 26 messages via NMEA0183. This Panbo article provides more info on this issue.
To help the dealer better understand some of these finer points of the AIS system, we sent him a copy of our Non-Idiot’s Guide to AIS that we produced for the British Marine Electronics Association. The 26 AIS messages are detailed on page 12 of this document and the NMEA2000 PGNs are on page 13.
This presentation is a few years old now but is still a useful reference for anyone wanting to learn a bit more about AIS technology. To download a copy click here.