AUTOMATIC IDENTIFICATION SYSTEM

AIS

          AIS IS A VESSEL TRACKING SYSTEM CAPABLE  OF TRANSMIT AND RECEIVE NAVIGATION INFORMATION AUTOMATICALLY BETWEEN AIS  EQUIPPED VESSEL AND COASTAL AUTHORITIES. UNLESS RADAR AIS CAN SEEN SHIPS BEHIND LARGE OBJECTS SUCH AS OTHER SHIPS OR POINT OF LAND MEANS BENT OF RIVER AND BEHIND THE ISLAND WITHIN THE VHF RANGE

OBJECTIVES OF AIS

AIS IS INTENDED TO ENHANCE SAFETY OF LIFE AT SEA, THE SAFETY AND EFFICIENCY OF NAVIGATION, AND THE PROTECTION OF THE MARINE ENVIRONMENT. THE PURPOSE OF AIS IS TO HELP IDENTIFY VESSELS; ASSIST IN TARGET TRACKING, SIMPLIFY INFORMATION EXCHANGE (E.G. REDUCE VERBAL MANDATORY SHIP REPORTING); AND PROVIDE ADDITIONAL INFORMATION TO ASSIST SITUATION AWARENESS. IN GENERAL, DATA RECEIVED VIA AIS WILL IMPROVE THE QUALITY OF THE INFORMATION AVAILABLE TO THE WATCH KEEPING OFFICER WHETHER AT A SHORE SURVEILLANCE STATION OR ON BOARD A SHIP. 

TYPES OF AIS

THERE ARE TWO TYPES OF AIS

AIS CLASS A & AIS CASS B

CLASS A AIS

CLASS A AIS TRANSPONDERS (SOLAS COMPLIANT) OPERATE USING SELF-ORGANIZING TDMA (SOTDMA) BROADCAST MODE AND TRANSMIT INFORMATION EVERY 2 TO 10 SECONDS WHILE UNDERWAY (EVERY 3 MINUTES WHILE AT ANCHOR) AT A POWER LEVEL OF 12.5 WATTS. STATIC AND VOYAGE RELATED VESSEL INFORMATION, SUCH AS THE VESSEL'S NAME, ARE TRANSMITTED EVERY 6 MINUTES. THEY ARE REQUIRED TO HAVE A DSC (156.525 MHZ) RECEIVER, EXTERNAL GPS, HEADING, AND RATE OF TURN INDICATOR. CLASS A AIS (AUTOMATIC IDENTIFICATION SYSTEM) TRANSPONDERS ALSO TRANSMIT AND RECEIVE SAFETY-RELATED TEXT MESSAGES.

A CLASS A AIS TRANSPONDER BROADCASTS THE FOLLOWING INFORMATION EVERY 2 TO 10 SECONDS WHILE UNDERWAY, AND EVERY 3 MINUTES WHILE AT ANCHOR:

• MMSI NUMBER
• NAVIGATION STATUS
• RATE OF TURN SPEED OVER GROUND
• POSITION ACCURACY
• LONGITUDE AND LATITUDE 
• COURSE OVER GROUND
• TRUE HEADING
• TIME STAMP

IN ADDITION, THE CLASS A AIS UNIT BROADCASTS THE FOLLOWING INFORMATION EVERY 6 MINUTES:

• MMSI NUMBER
• IMO NUMBER
• RADIO CALL SIGN
• VESSEL NAME
• TYPE OF SHIP/CARGO
• DIMENSIONS OF SHIP
• LOCATION ON SHIP WHERE REFERENCE POINT FOR POSITION REPORTS IS LOCATED
• TYPE OF POSITION FIXING DEVICE - VARIOUS OPTIONS FROM DIFFERENTIAL GPS TO UNDEFINED
• DRAUGHT OF SHIP
• DESTINATION -
• ESTIMATED TIME OF ARRIVAL AT DESTINATION - MONTH, DAY, HOUR, AND MINUTE IN UTC

CLASS B AIS

CLASS B AIS  TRANSPONDERS OPERATE USING CARRIER-SENSE TDMA (CSTDMA) BROADCAST MODE AND TRANSMIT INFORMATION EVERY 30 TO 180 SECONDS AT A POWER LEVEL OF 2 WATTS. STATIC DATA, SUCH AS THE VESSEL'S NAME, IS TRANSMITTED EVERY 6 MINUTES.                                                                                          CLASS B AIS TRANSPONDERS ALSO PROVIDE STATIC VESSEL INFORMATION EVERY SIX MINUTES HOWEVER THE INFORMATION ONLY INCLUDES:

• MMSI
• RADIO CALL SIGN
• VESSEL NAME
• LENGTH AND BEAM OF VESSEL
• TYPE OF VESSEL

POSITION UPDATES FOR CLASS B TRANSPONDERS ARE BROADCAST LESS OFTEN THAN CLASS A TRANSPONDERS. VESSELS GOING LESS THAN 2 KNOTS TRANSMIT POSITION UPDATES EVERY 3 MINUTES WHILE VESSELS STEAMING MORE THAN 2 KNOTS TRANSMIT POSITION INFORMATION EVERY 30 SECONDS.

RANGE OF AIS

IT OPERATES IN THE VHF BAND. THE TWO FREQUENCIES USED WORLDWIDE ARE 161.975 AND 162.025 MHZ (CHANNELS 87B AND 88B, OR AIS1 AND AIS2). THE SYSTEM COVERAGE RANGE IS SIMILAR TO OTHER VHF APPLICATIONS, ESSENTIALLY DEPENDING ON THE HEIGHT OF THE ANTENNA. ITS PROPAGATION IS SLIGHTLY BETTER THAN THAT OF RADAR, DUE TO THE LONGER WAVELENGTH, SO IT’S POSSIBLE TO “SEE” AROUND BENDS AND BEHIND ISLANDS IF THE LAND MASSES ARE NOT TOO HIGH. A TYPICAL VALUE TO BE EXPECTED AT SEA IS NOMINALLY 20 NAUTICAL MILES. WITH THE HELP OF REPEATER STATIONS, THE COVERAGE FOR BOTH SHIP AND VTS STATIONS CAN BE IMPROVED CONSIDERABLY. 

APPLICATION OF AIS  

ALL SHIPS OF 300 GROSS TONNAGE AND UPWARDS ENGAGED ON INTERNATIONAL VOYAGES AND CARGO SHIPS OF 500 GROSS TONNAGE AND UPWARDS NOT ENGAGED ON INTERNATIONAL VOYAGES AND PASSENGER

SHIPS IRRESPECTIVE OF SIZE SHALL BE FITTED WITH AIS