An AIS position report transmits dynamic vessel data including location, speed, course and status via VHF radio. This information originates from the ship’s connected sensors and is broadcast to nearby receivers for situational awareness.
The report carries essential dynamic parameters such as position accuracy, timestamp, navigational status and speed over ground. The position and time values are derived directly from the vessel’s electronic position-fixing receiver, ensuring they reflect the sensor’s current output rather than an independent verification.
Regulatory bodies classify these transmissions into specific message formats. USCG identifies AIS Messages 1, 2 and 3 as Class A position reports and Message 18 as the standard Class B position report. Each message type encapsulates the same core dynamic data but may differ in update rates and data fields depending on the equipment class.
The frequency of these broadcasts is not fixed; it adapts based on the vessel’s speed, movement state and the specific reporting mode active at the time. Consequently, position reports arrive significantly more often than static or voyage-related data updates to maintain real-time tracking accuracy.
Because the reported position relies entirely on the transmitting station’s sensor data, it may not coincide exactly with a target detected by radar. Users must understand that this is a transmitted value based on the source equipment, not an independently measured or guaranteed position.
