THE BIG QUESTION Will commercial AIS integrate with my current display?
QI’m thinking of replacing the electronics on my boat and I’ve got a great offer on a package that includes radar, chartplotter and Class A AIS. The AIS looks like a great bit of kit, but will Class A integrate properly with my Raymarine chartplotter, and what will the power draw be? Peter Smith
Derek Gilbert of Raymarine replies:
AClass A AIS is used by commercial vessels and Class B mainly on leisure craft under 24m. Class A AIS transceivers will display and transmit more information about the vessel onto which they are installed. However, basic vessel information, such as name, MMSI, and heading, apply to both classes.
Most Class A AIS transceivers use NMEA0183 data protocol and so must be connected into navigation displays using this. Bear in mind this is generally at a high baud rate: 38,400 and the navigation screen will need this capability. Standard NMEA0183 operates at 4,800 baud rate.
If a data converter is to be used to interface the Class A AIS to the navigation screen, make sure it’s suitable for this higher data baud rate.
Commercial Class A AIS transceivers may require True Heading (HDT) and Rate of Turn (ROT) data. This is based on the vessel’s gross tonnage and is a requirement for navigation authorities around the world, including inland waterways such as the Rhine. This presents three potential issues:
The NMEA data sentence for True Heading may not be available in the onboard network. Therefore, it requires a True heading source from a 3rd party heading device such as a GPS or gyro compass.
Rate of Turn is also a requirement in some sea or inland waterways. This may also require a third party device.
If the Class A AIS is installed in a network without the relevant HDT and
ROT Data, the AIS will function but both ROT and HDT alarm notifications will be triggered and constantly sound.
On non-commercially coded vessels, the alarms can be disabled and the data will display in the same way as Class B AIS. The power consumption will be higher on Class A, but only by some 5-8 Watts.