Automatic Identification System (AIS) is an automated tracking system used on ships and by Vessel Traffic Services (VTS) for identifying and locating Vessels by electronically exchanging data with other nearby ships and VTS stations. AIS information supplements marine radar, which continues to be the primary method of collision avoidance for water transport. What’s the difference between class A & B Transceivers ? The type of transceiver has a number of impacts on AIS capability, primarily information from a class A transceiver will always be prioritized and be shown to other ships in the area, whereas AIS information from a class B transceiver may not be shown until or if there is room on the AIS channel.
Class B transceivers are cheaper and transmits less frequently as they listen
for a couple of milliseconds to hear whether a large ship is transmitting before
it transmits its own message. Class A AIS transponders transmit at 12W and transmissions are sent every few seconds. Class B units are fully integrated into the AIS system but have a lower 2W transmit power and only send their data every 30 seconds. They also require a chart plotter to display target data. Large ships can choose not
to show AIS stations of class B on their displays.