AIS
The Next On-Board Necessity

by Stuart Reininger
Senior Editor

A black night, a busy traffic lane, multiple radar targets and a VHF that, every few moments, bursts into life, shattering the silence of the darkened wheelhouse. Invariably, the voice on the radio is attempting to contact or identify a ship whose actions, or merely its presence, is a cause of concern.

With each transmission, the watch officer of every ship on the band instinctively determines whether or not the call applies to his vessel. Is own ship the vessel to starboard of the calling ship; is the radar blip astern trying to negotiate a passing agreement or is it another pair of ships further down the lane?

Ship identification in close quarters is often performed in reference to nearby buoys or landmarks and lat/long coordinates. And all too often, and sometimes too late, the watch officer discovers that the ship he’s talking to, isn’t the one he’s looking at or has on the screen.

The aviation industry years ago saw that scenario’s potential for disaster and today cargo and passenger aircraft are required to carry transponders that automatically identify them and continuously transmit their location.

Last December, in a move likely to be appreciated by any captain who has ever lost sleep while trying to identify an unknown radar target, the IMO's Maritime Safety Committee adopted mandatory requirements for the carriage of automatic identification systems (AIS) capable of providing information about the ship to other ships and to coastal authorities. The regulation is part of a new SOLAS chapter V expected to enter into force on July 1, 2002.

As we’ve discussed in previous issues, that same new chapter also ushers in mandatory requirements for the carriage of VDR’s (voyage data recorders). The phase in requirements for both AIS and VDR’s may be accelerated for some ships if the European Union succeeds in initiatives it is pressing at IMO as part of its “post-Erika” thinking.

Meantime: click here to see the proposed IMO schedule for mandatory carriage of AIS

WHAT DOES IT DO?
So, what exactly is AIS, how does it work and what does it transmit?

The two most immediate points are that the system is fully automatic and operates on a dedicated VHF band; therefore, its range is roughly equivalent to any VHF broadcast. AIS depends on transponders which continually transmit a ship’s identification; the most likely means of identification would be the appropriate Maritime Mobile Service Identity (MMSI) number.

According to IMO resolution MSX.74(69), Annex 3 Chapter 6, shipboard AIS systems must be able to perform the following functions:

1. Automatically provide information on the ship’s identity, type, position course, speed, navigational status and other safety-related matters to appropriately equipped shore stations, other ships and aircraft.
   
2. Receive automatically such information from similarly fitted ships
   
3. Monitor and track ships
   
4. Exchange data with shore based facilities.
   

The information provided by the AIS comes under the following three general categories:

• Static information: this includes: ship’s IMO number (where available), call sign and name, length and beam, type of ship, location of position-fixing antenna on the ship (aft of bow and port or starboard of centerline
  
• Dynamic information: this includes: ship’s position with accuracy indication and integrity status, time in UTC, course over ground, speed over ground, heading. Other dynamic information such as rate of turn during maneuvering and, when necessary, angle of heel and pitch and roll.
  
• Voyage related information: this includes: ship’s draft, cargo type, destination and ETA (at master’s discretion)
  
• A route plan, including waypoints can also be transmitted as well as short, safety-related messages.
  

Due to the constantly changing nature of the required information, specific update rates for transmissions have been provided for in the regulations. For instance, static information and voyage-related information will be automatically transmitted every six minutes and on request.

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