Frequently Asked Questions
AIS is short for Automatic Identification System previously referred to as UAIS.
What is the purpose of AIS? ?
IMO Resolution MSC. 74 (69) states that AIS should "improve the safety of navigation by assisting in the efficient navigation of ships, protection of the environment, and operation of Vessel Traffic Services (VTS), by satisfying the following functional requirements:
1. in a ship-to-ship mode for collision avoidance;
2. as a means for littoral States to obtain information about a ship and its cargo; and as a VTS tool, i.e. ship-to-shore (traffic management).
What ships carry AIS?
By the end of 2004 all Solas vessels over 500GT (300GT on international voyages) and all passenger vessels irrespective of size will be required to carry AIS and to maintain the system in operation at all times. This system is referred to as Class A AIS. Non Solas vessels may carry this system on a voluntary basis.
Standards for a lower cost Class B AIS for non Solas vessels are at an advanced stage of development.
How does AIS operate?
The key to AIS operation is precise timing provided by GPS and a technique known as SOTDMA (Self Organising Time Division Multiple Access) which supports a high volume of short messages.
Shipborne AIS units can transmit and receive on two frequencies set aside for AIS known as AIS 1 and AIS 2 (161.975 MHz -87B and 162.025 MHz - 88B). In certain circumstances units in a particular area may be automatically directed to an alternative channel. Each unit has a DSC Channel 70 receiver for channel management. Each unit has a GPS receiver for timing purposes and as a secondary position source should the ships position device fail.
What role does AIS perform for the mariner?
The primary role of AIS is as a ship tracking and identification system which operates in the Marine VHF band. AIS equipment transmits dynamic information automatically at intervals of between 2 and 12 seconds depending on the vessel's speed or 3 minutes if at anchor. Transmissions will be received by other AIS equipped vessels and shore stations. A separate message with static and voyage related data is transmitted every 6 minutes.
AIS also has a role as an Aid to Navigation and applications in maritime security, search and rescue, and traffic monitoring/management. Beyond this a range of commercial applications are also possible.
What information is transmitted?
Three types of information are transmitted.
Static information such as MMSI, Call Sign, Name, IMO Number, Length, Beam, Ship type and antenna location. This information would be entered at installation and would not require frequent changes.
Dynamic information such as position, course over ground, heading, speed, rate of turn and status. This information is generally updated automatically from the ship's own sensors and equipment.
Voyage related information such as draught, cargo, persons on board, destination, ETA and route plan. This information is generally manually entered and updated by the bridge team.
What user input is required?
User input is generally limited to the input of voyage related data.
May shipborne AIS be switched off?
The December 2002 amendments to Solas Chapter V provide that "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".
How does AIS perform as an Aid to Navigation?
The Commissioners of Irish Lights will use AIS technology to improve the Aids to Navigation service to mariners.
Where AIS units are fitted directly on aids to navigation they will communicate directly with the shipborne AIS to confirm that the aid is in its charted position and functioning correctly or advise of any deficiencies. Additional functionality can also be provided to give details of wind, wave, tide and similar information.
Where aids to navigation are monitored by means other than AIS a shore station can broadcast this information so that it appears to come from the aid. Such broadcasts are termed synthetic aids to navigation and can give all of the information as though from the aid itself.
It will also be possible to establish virtual aids to navigation which are transmitted from shore stations but show on AIS at a specified charted position. Such aids would have a value as a fast response for wrecks or new dangers prior to a physical aid being established, or for specialised uses.
How will AIS Targets be displayed on the Bridge?
There is still considerable debate on the most appropriate method of displaying AIS information. The mandatory carriage requirement is for a minimum keyboard and display (MKD). This is an alphanumeric display similar in size to common GPS receivers. Some manufacturers incorporate a small graphic display into this MKD. While such a display meets the carriage requirement most mariners are of the view that the targets should also be displayed on Radar and/or ECDIS.
Display on Radar or ECDIS opens up a range of issues relating to target correlation, data fusion, display modes, information layering and information overload.
The IMO have published minimum guidelines including basic symbology in SN Circ. 217.
The IEC Technical Committee 80, Working Group 13 are tasked with establishing an overall standard for general requirements that encompasses the display of all shipboard navigation information to make all displays more uniform and consistent. This will deal with many but not all of the AIS display issues.
Will AIS interfere with other on board systems?
AIS transmits at frequent intervals on VHF and if incorrectly installed can interfere with other on-board equipment including DSC. For this reason strict attention should be paid to the installation guidelines.
Can the system become overloaded?
The AIS position message is approximately 26 milliseconds long allowing 2250 message slots per minute on each frequency so overloading is unlikely. In very busy traffic areas the system automatically shrinks its coverage radius to give priority to closer targets.
What happens in the event of a GPS failure?
There is provision in the event of a GPS failure for stations in the area to take their timing from a nominated station.
Can anyone establish an AIS station?
AIS operates in the Marine VHF Band so a radio licence is required for both shipborne and shore stations.
Will all AIS vessels be monitored from shore?
The 'VTM Directive' (Directive 2002/59/EC establishing a Community vessel traffic monitoring and information system) requires AIS monitoring of IMO recognised Traffic Separation Schemes, Routing Systems and VTS areas. The Irish and United Kingdom governments are putting in place systems to meet these requirements. It is likely that traffic monitoring will extend beyond the minimum requirements of the directive.
Will AIS replace mandatory reporting by VHF?
It is expected that in time AIS will replace the requirement for voice reporting at mandatory reporting points. However, for the present the existing requirements still apply.
Will AIS replace radar?
No. There always will be ships without AIS onboard. Radar detects targets independent of the target's onboard equipment.
How does the AIS supplement the radar information?
In addition to radar, AIS has the following benefits:
Automatic vessel identification
Automatic provision of heading, course over ground (COG) and speed over ground (SOG).
Improved vessel tracking (no target swap)
Wider geographical coverage, although in some circumstances, eg: mountainous areas, this may only be achieved with the provision of shore-based repeater stations.
Greater positional accuracy, dependent on the position input sensor.
Provides information in radar shadow area ('sees' around bends and behind islands)
Near real time manoeuvring data
No loss of targets in sea, rain, and snow clutter
What are the main limitations of AIS?
AIS is like all other broadcast devices and is sensitive to radio frequency interference. It is also subject to the limitations of VHF propagation. AIS relies on Global Navigation Satellite Systems (GNSS) data for position and timing inputs, which are central to its functioning; as such, it is subject to the vulnerabilities inherent in satellite navigation systems. Mariners are cautioned that some vessels in their vicinity may not be fitted with AIS.
How does the master know that his AIS unit is working properly?
A built-in integrity test (BIIT) running continuously or at appropriate intervals;
Monitoring of the availability of the data
An error detection mechanism of the transmitted data; and
Error checking of the data received.
If no sensor is installed or if the sensor (G: the gyro) fails to provide data, the AIS automatically transmits the "not available" data value. However, the integrity check cannot validate the accuracy of the data received by the AIS. The AIS requires that an alarm output (relay) be connected to an audible alarm device or the ship's alarm system, if available. Alternatively, the BIIT alarm system may use the alarm messages' output on the Presentation Interface (PI), provided its alarm system is AIS compatible.
How does the master know that the information received from another AIS unit is accurate?
The master can authenticate the information from his AIS unit by cross-checking with the vessel's radar and by visual observations.
Can I send a letter to my agent via AIS?
No. AIS is not intended for routine messaging on the two designated AIS frequencies. AIS is mainly used for identifying and tracking other ships. However, it allows the transmission of safety related messages on the AIS designated frequencies.
When is a vessel permitted to sail without operational AIS equipment?
If the vessel comes under the SOLAS Regulations, the vessel may be allowed to proceed to a port where repairs can be carried out. However, if the vessel does not fall under SOLAS Regulations, it depends on the regulations of the national maritime administrations.
Why do AIS messages not include the rudder angle?
Rudder angle information is not always representative of the actual manoeuvre of the vessel. Transmitting rudder angle information may mislead the recipient and can be dangerous.
How do I display AIS information?
The stand-alone minimum keyboard display (MKD) is one of the approved methods of displaying AIS information. The approval of AIS-capable radars & ECDIS is underway. Manufacturers are the best source of information on this issue.
Can I connect my GPS to the AIS?
The GPS connected to the AIS must fulfil the relevant IMO Performance Standard and IEC Test Standard. This means that the positional output from the GPS must be in WGS84 format and among others, there is no dead reckoning permitted.
Can I connect my gyro compass to the AIS?
The gyro compass must be connected to the AIS unit on board SOLAS vessels. Without heading information, the presentation of the ship shape must not be generated. However, in this case, the isosceles triangle representing the ship's position will be aligned with the COG (without the heading marker) on the display of receiving stations.
What is the accuracy of navigational information provided?
The accuracy of navigational information such as position, course, speed, etc, depends on the accuracy of the sensors used. There is an indication of the positional accuracy transmitted by AIS, depending on whether GMSS or DGNSS is used. Further, the accuracy of data, such as voyage related data, depends on the accuracy with which this entered and the frequency of its update. Masters must bear in mind that a third party enters the information they receive and should therefore take this into account.
How will AIS contribute to the prevention of collision?
AIS should not be used as an anti-collision device in isolation. It should be used in conjunction with all means available to assist the mariner in assessing the risk of collision. It is important to note that there will always be other vessels that do not have AIS.
Is AIS information stored somewhere?
Ashore - This is a matter for national administrations. Onboard - This depends on the other equipment installed.
For what purposes could the stored or recorded data be used?
The data could be used for a variety of purposes, such as:
Risk analysis, and
Are naval ships required to fit AIS?
No. The SOLAS Convention does not apply to them. However, Administrations may dictate the use of AIS on board naval vessels.
What are the differences between AIS Class A and AIS Class B Stations?
Class A meets SOLAS carriage requirements and is now in the process of implementation. Class A units are in full production. They can be required by administrations for other vessels as domestic or regional carriage requirements dictate.
Class B is proposed for vessels not covered by SOLAS carriage requirements. It is still under investigation for feasibility of technical, practical, and cost concepts. The Class B standard is under development.
MSC Resolution.140(76) Dec. 5, 2002 refers
What methods are available to prevent inappropriate use of AIS?
This is a matter for national Administrations to control. However, the protection of AIS frequencies and information etc, should be embroiled in the national legislation of seafaring nations.
Are AIS messages limited to safety information?
Yes. ITU-R Recommendation M.1371-1 limits AIS transmissions on AIS designated channels to maritime safety related messages. In addition, IMDO has permitted the exchange of seven other ancillary messages, for a test period of four years. Examples of such messages are number of persons on board, meteorological and hydrological information, indication of dangerous cargo, status of fairway, etc.
Is there a limit on the length of AIS messages?
Yes. All messages have a maximum allowable limit. For example, no more than 64 characters can be transmitted in one text message.
Will AIS messaging grow to include commercial usage?
No - commercial messages cannot be transmitted on designated, safety-related frequencies, ie: AIS1 and AIS2. Further, AIS is not the ideal tool for routine commercial correspondence. It is best to use other available means for this purpose.
Is it possible to transmit fraudulent messages?
Although it is possible to generate and transmit false messages, mariners are cautioned that there may be severe penalties imposed by national administrations for these actions, in accordance with national legislation.
Should AIS data be integrated on the same display as information from other sensors in a VTS?
Ideally, yes. All sensor information should be integrated on a single display.
Can I get DGNSS corrections over the AIS link?
Yes, if the Administration decides to do so. The message structure and technical approach have been defined in the IALA AIS Guidelines.
How is meteorological/hydrological information displayed?
A message structure has been adopted by IMO. Work is progressing on the various methods to display this information.
Is there any calibration of the AIS equipment needed?
No. A correctly installed AIS unit should not need any further calibration to continue operating. National Administrations may, however, have their own requirements.
Is there any set up (regular/frequent/initial) of the AIS equipment needed?
Yes. Static data (callsign, MMSI, IMO number etc) should be entered upon installation and should be in accordance with the ship's registration documents. Voyage-related data must be entered at the commencement of each voyage or if there are any changes. It is recommended that both static and voyage-related data be checked and updated at appropriate intervals, as required.
Is AIS mandatory for inland waterways?
No. This is a matter for Administrations.
Is there any training on the use of AIS available?
The manufacturers may well give initial training on their equipment. However, it is recommended that ship owners and managers incorporate such training in their ISM procedures.