Chapter 10: AIS 111
10.1 Background information
AIS broadcasts information between vessels and shore-based sta-
tions on VHF frequencies in the maritime band. This information is
used to provide fast, automatic and accurate collision-avoidance
data. It can operate in radar blind spots and can detect smaller (AIS-
equipped) vessels than radar can.
AIS does not replace radar, because it is unable to detect land or
navigation beacons.
Classes of AIS data
AIS data is defined as Class A or Class B. The sending and receiv-
ing of Class A data is compulsory for larger vessels. You will
therefore be able to view all larger vessels on your AIS display.
Not all AIS receivers will decode all information and not all of the
Class A vessels input all of the required AIS data. For example,
some inexpensive AIS Class B receivers do not decode and output
the ship’s name, IMO number and vessel data.
Class B data is applicable to smaller vessels and is not compulsory.
Do not assume that your AIS will display data for all smaller vessels
in your area.
The following information can be transmitted by a Class A AIS
system:
• Static data: ship name, type, MMSI number, call sign, IMO
number, length, beam and GPS antenna location.
• Voyage data: draft, cargo, destination, ETA, other relevant
information.
• Dynamic data: time, position, COG, SOG, gyro heading, rate of
turn, navigational status.
• Dynamic reports: speed and status.
• Messages: alarm and safety.
