Marine Dictionary & Glossary of Boating Terms

Automatic Identification System

Similar Terms: AIS,Class A,Class B,AIS Receiver

Automatic Identification System (Acronym: AIS) is a way of identifying a vessel's position, course, speed and identity through VHF digital information, often used as an anti-collision system. 

Marine AIS is particularly useful in identifying targets that maybe obscured by poor visibility, or behind larger targets like low islands or large ships that radar can't penetrate. Boats with an AIS transponder are represented on other boats with an AIS Receiver on a map or radar image on a Multifunction Display.

Static data is information about the vessel which must be programmed into the AIS transceiver at the time of installation. Software is included that enables the AIS to be programmed with ship’s data including;

• Maritime Mobile Service Identity (MMSI)
• Vessel name
• Vessel call sign (if available)
• Vessel type
• Vessel dimensions

Owners of Marine AIS Class A and B Transponders must hold a Marine Radio Operator’s Certificate of Proficiency to be able to apply for a MMSI.

No MMSI is required to have an AIS Reciever onboard your vessel.

More about Class A and Class B AIS

There are two main classes of AIS, Class A and Class B, as well as different types of AIS used for shore stations (AIS Base Stations), Aids To Navigation (AIS AtoN), AIS on search and rescue aircraft and AIS search and rescue transmitters (AIS SART).

Class A AIS is mandated by the International Maritime Organisation (IMO) for vessels of 300 gross tonnage and upwards engaged on international voyages, cargo ships of 500 gross tonnage and upwards not engaged on international voyages, as well as passenger
ships (more than 12 passengers), irrespective of size.

Class B is for voluntary fits to power and sail boats alike. Class B AIS is intended for non-SOLAS vessels. It is not mandated by the International Maritime Organisation (IMO) and has been developed for vessels such as work craft and pleasure craft.

AIS uses Time-Division Multiple Access (TDMA) across two dedicated VHF frequencies – AIS 1 (161.975 MHz) and AIS 2 (162.025 MHz). Although Class A and Class B both use TDMA, Class A units use a Self-Organized TDMA (SOTDMA; Self-Organizing amongst Class A's) whereas Class B units use CSTDMA (Carrier-Sense TDMA, polite to Class A's). Class B's therefore determine free slots in the VHF wavelengths and decide when to transmit a report, enabling a ‘politeness’ factor, so as not to interfere or cause degradation of Class A signals.

The transmission of signals and informaiton varies from every 2 seconds to every 3 minutes depending on the speed of the vessel; more signals at higher speeds.

Source: http://www.amsa.gov.au