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AIS Overview

AIS Basics | Class A vs Class B AIS | IMO Requirements | Shine Micro Exclusives

AIS Basics


Screen shots captured with Coastal Explorer by RosePoint Navigation.

An Automatic Identification System (AIS) is used for identifying and monitoring maritime traffic. AIS sends and receives vessel identification information which can be displayed on a laptop computer or chart plotter. Information such as vessel name, radio call sign, navigational status (eg. at anchor, under way using engine), speed, heading, type of ship/cargo, destination, and estimated time of arrival are all examples of information that can be displayed.

AIS Broadcasts:

  • MMSI Number
  • Location (GPS)
  • Name of Ship
  • Radio Call Sign
  • Speed
  • Vessel Type
  • And more
Some applications for AIS include:
  • Stewardship
    Monitoring marine sanctuaries for environmental protection
  • Safety
    Detailed information for collision avoidance and emergency response
  • Security
    Accident and crime prevention through Maritime Domain Awareness
How AIS Works: Click image for a larger view.

(Automatic Identification System)

How AIS Works, diagram credit: Finnish Maritime Administration

One application for shore-side AIS: Stewardship

An MMSI number is a unique identifier assigned to a boat. Only one number is assigned for all applicable electronics on the vessel, such as an AIS (Automatic Identification System) transponder, DSC Radio, and EPIRB. MMSI registration includes contact information to be used in case of an emergency. More information about MMSI numbers can be found on our About MMSI page. You can register your MMSI number with Shine Micro for inclusion in the combined MMSIspace database, which works like a directory for MMSI numbers and includes live, interactive mapping features.

The United States Coast Guard describes AIS as follows:

Picture a shipboard radar display, with overlaid electronic chart data, that includes a mark for every significant ship within radio range, each as desired with a velocity vector (indicating speed and heading). Each ship "mark" could reflect the actual size of the ship, with position to GPS or differential GPS accuracy. By "clicking" on a ship mark, you could learn the ship name, course and speed, classification, call sign, registration number, MMSI, and other information.
Maneuvering information, closest point of approach (CPA), time to closest point of approach (TCPA) and other navigation information, more accurate and more timely than information available from an automatic radar plotting aid, could also be available. Display information previously available only to modern Vessel Traffic Service operations centers could now be available to every AIS-equipped ship.
With this information, you could call any ship over VHF radiotelephone by name, rather than by "ship off my port bow" or some other imprecise means. Or you could dial it up directly using GMDSS equipment. Or you could send to the ship, or receive from it, short safety-related email messages.

The AIS is a shipboard broadcast system that acts like a transponder, operating in the VHF maritime band, that is capable of handling well over 4,500 reports per minute and updates as often as every two seconds. It uses Self-Organizing Time Division Multiple Access (SOTDMA) technology to meet this high broadcast rate and ensure reliable ship-to-ship operation.

 


Class A AIS vs. Class B 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.

Class B AIS (Automatic Identification System) 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. A DSC receiver and heading are optional. Transmitting safety-related text messages is optional and they can only be pre-configured into Class B AIS transponders.

The similarities and differences of Class A AIS and Class B AIS are summarized below:

Class A AIS and Class B AIS Characteristics

 

Class A AIS (SOLAS Compliant)

Class B AIS

Transmit Power

12.5 watts (nominal), 2 watts (low power)

2 watts

Unique Communication Access Scheme

SOTDMA (Self-Organizing amongst Class A's)

CSTDMA (Carrier-Sense polite to Class A's)

Frequency Range

156.025 - 162.025 MHz @ 12.5/25 KHz, DSC (156.525 MHz) is required

156.025 - 162.025 MHz @ 25 KHz, DSC (156.525 MHz) and 12.5 KHz are optional

Miscellaneous

External GPS, Heading, and Rate of Turn Indicator are Required

Heading is optional

Safety Text Messaging

Transmits and Receives

Transmit is optional and only pre-configured

Commonly Used AIS Messages

Msg ID

Description

Class A AIS

Class B AIS

Vessel Speed (knots)

Transmit Frequency (seconds)

 

 

 

 

 

 

1

Scheduled Position Report

AIS (Automatic Identification System)

 

Moored

180 s

1

Scheduled Position Report

AIS (Automatic Identification System)

 

0 to 14 kts

10 s (3.3 s if also changing course at + 5°)

1

Scheduled Position Report

AIS (Automatic Identification System)

 

15 to 23 kts

6 s (2 s if also changing course at + 5°)

1

Scheduled Position Report

AIS (Automatic Identification System)

 

> 23 kts

2 s

2

Assigned Scheduled Position Report

AIS (Automatic Identification System)

 

Moored

180 s

2

Assigned Scheduled Position Report

AIS (Automatic Identification System)

 

0 to 14 kts

10 s (3.3 s if also changing course at + 5°)

2

Assigned Scheduled Position Report

AIS (Automatic Identification System)

 

15 to 23 kts

6 s (2 s if also changing course at + 5°)

2

Assigned Scheduled Position Report

AIS (Automatic Identification System)

 

> 23 kts

2 s

3

Special Position Report, Response to Interrogation

AIS (Automatic Identification System)

 

N/A

N/A

5

Scheduled Static and Voyage Related Vessel Data Report

AIS (Automatic Identification System)

 

N/A

360 s

18

Standard Class B AIS Equipment Position Report

 

AIS (Automatic Identification System)

< 2 kts

180 s

18

Standard Class B AIS Equipment Position Report

 

AIS (Automatic Identification System)

> 2 kts

30 s

19

Extended Class B AIS Equipment Position Report; Response to Interrogation

 

AIS (Automatic Identification System)

N/A

N/A

24A

Static Data Report-Name of Ship

 

AIS (Automatic Identification System)

N/A

360 s

24B

Static Data Reprt-Static Data

 

AIS (Automatic Identification System)

N/A

Transmitted within 1 minute following Message 24A

Class A AIS

Identifier Information

Class B AIS

Receive

Transmit (Msg ID)

 

Transmit (Msg ID)

Receive

AIS (Automatic Identification System)

1, 2, 3, 5

MMSI #

18, 19, 24A, 24B

AIS (Automatic Identification System)

AIS (Automatic Identification System)

1, 2, 3

Navigation Status

 

AIS (Automatic Identification System)

AIS (Automatic Identification System)

1, 2, 3

Rate of Turn

 

AIS (Automatic Identification System)

AIS (Automatic Identification System)

1, 2, 3

Speed Over Ground

18, 19

AIS (Automatic Identification System)

AIS (Automatic Identification System)

1, 2, 3

Position Report

18, 19

AIS (Automatic Identification System)

AIS (Automatic Identification System)

1, 2, 3

Course Over Ground

18, 19

AIS (Automatic Identification System)

AIS (Automatic Identification System)

1, 2, 3

True Heading

18, 19

AIS (Automatic Identification System)

AIS (Automatic Identification System)

1, 2, 3

Time Stamp

18, 19

AIS (Automatic Identification System)

AIS (Automatic Identification System)

5

IMO Number

 

AIS (Automatic Identification System)

AIS (Automatic Identification System)

5

Radio Call Sign

24B

AIS (Automatic Identification System)

AIS (Automatic Identification System)

5

Name of Ship

19, 24A

AIS (Automatic Identification System)

AIS (Automatic Identification System)

5

Type of Ship and Cargo Type

19, 24B

AIS (Automatic Identification System)

AIS (Automatic Identification System)

5

Overall Dimension/Reference for Position

19, 24B

AIS (Automatic Identification System)

AIS (Automatic Identification System)

5

Type of Electronic Position Fixing Device

19

AIS (Automatic Identification System)

AIS (Automatic Identification System)

5

Estimated Time of Arrival

 

AIS (Automatic Identification System)

AIS (Automatic Identification System)

5

Maximum Present Static Draught

 

AIS (Automatic Identification System)

AIS (Automatic Identification System)

5

Destination

 

AIS (Automatic Identification System)


IMO Requirements

The standards and regulations of AIS are established by the International Maritime Organization. The majority of maritime traffic has been required to operate AIS (Automatic Identification System) equipment since July of 2004, as stated below:

Modifications to Chapter V (Safety of Navigation) contain a new timetable for the fitting of Automatic Information Systems (AIS). Ships, other than passenger ships and tankers, of 300 gross tonnage and upwards but less than 50,000 gross tonnage, will be required to fit AIS not later than the first safety equipment survey after 1 July 2004 or by 31 December 2004, whichever occurs earlier. Ships fitted with AIS shall maintain AIS in operation at all times except where international agreements, rules or standards provide for the protection of navigational information.

Furthermore, Title 33 of the United States Code of Federal Regulations states that:

Self-propelled vessels of 65 feet or more in length, other than passenger and fishing vessels, in commercial service and on an international voyage, not later than December 31, 2004.

The US Congress is considering requiring ships subject to the Bridge-to-Bridge Radiotelephone Act, small passenger vessels, and commercial towing vessels while towing, to also carry AIS (Automatic Identification System) equipment.

Additional details about AIS carriage requirements and questions frequently asked may be found on the US Coast Guard website.


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