Vessels transmit several data fields via AIS. The information in each AIS message can be divided into two categories:
Static & voyage related information is provided by the crew of the vessel and is transmitted every 6 minutes.
IMO number: a unique reference that is linked to the hull and never changes in one vessel's lifetime, regardless of a change in owner, flag or name
Callsign: international radio call sign assigned by national licensing authorities
Name: name of the vessel, max. 20 characters
Type: The AIS ship type consists of two digits. The first digit represents the category of the vessel and the second digit provides information about the vessel's type of cargo.
Dimensions: indicates the dimensions of the vessel to the nearest meter
Location of the positioning system's antenna on board the vessel: distance from bow, stern, port and starboard sides in meters
Type of positioning system: GPS, DGPS, Loran-C, GLONASS, etc.
Draught: vertical distance between the waterline and the keel (bottom of the hull) - 0.1 to 25.5 meters
Destination: max. 20 characters
ETA (Estimated Time of Arrival) at destination: UTC month/date hours:minute
Please note that above-mentioned information is correct as long as the vessels' crew provides the system with the correct information.
Dynamic information is automatically transmitted depending on the vessels' speed and course while underway every 2 to 10 seconds and while a vessel is at anchor every 6 minutes. This applies to Class A transponders.
MMSI number: unique identification number with nine digits
AIS Navigational Status: manually set by the crew, e.g. "under way using engine", "at anchor", "not under command", "moored", "underway sailing", ...
Rate of Turn: right or left (from 0 to 720 degrees per minute)
Speed over Ground: from 0 to 102 knots (189 km/h) with 0.1-knot resolution (0.19 km/h)
Positional accuracy: longitude and latitude
Course over Ground: the actual path of a vessel between two points with respect to the seabed - relative to true north to 0.1°
Heading: compass direction in which the vessel's bow is pointed - 0 to 359 degrees
UTC seconds: the seconds' field of the UTC time when these vessels' data were generated
Class B transponders, compared to Class A transponders, send less data (not included are IMO number, Draught, Destination, ETA, Rate of Turn, Navigational Status) and the transmitting intervals are rarer.