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Automatic Identification System (AIS) What is AIS technology used for? AIS is used by ship operators to provide the highest level of navigational safety. It is also used by some ports to enhance security. AIS uses a shipboard VHF broadcast system to transmit and receive information about other ships, safety messages, environmental conditions and the status of aids-to-navigation (buoys). As of January 1, 2005, nearly every commercial ship over 65 feet in length in U.S. waters is required to send out identification and GPS information. How does AIS work? Static and dynamic navigational data is sent via VHF from ship to ship. Thanks to GPS technology, this data can include a ship's position. Other information broadcast by AIS is electronically obtained from a ship's Gyro Compass.

What is AIS:

The Universal Shipborne Automatic Identification System (AIS) is a system of transponders installed on vessels which transmit over two dedicated digital marine VHF channels. The data is sent from each vessel every few seconds and contains position and movement information such as course, speed, latitude, longitude, and rate of turn. Static information about the vessel is sent every few minutes and includes the name, type of ship, length, beam, draft, etc. Nearly all commercial ships are mandated to carry AIS transponders and each year more yachts, launches and work boats are fitting AIS equipment.

AIS Transponders: An AIS transponder receives and translates the AIS digital radio signals. It also sends AIS signals, making your vessel visible to others with AIS equipment. There are two types of transponders, Class A intended for SOLAS vessels and Class B for fitting on non-SOLAS category vessels. AIS transponders are sometimes referred to as transceivers in the marine industry.

AIS Receivers: An AIS receiver operates in the same way as transponder but is a receive only device. If your vessel has a receiver you are able to view vessels in your area but other vessels will not see you on their AIS equipment.

AIS Display: An AIS display interfaces with either a transponder or receiver to display the AIS radio signals in a useable format. A dedicated AIS display is very useful to allow critical safety information to always be available at a glance and can include features that arenít normally found in plotters or computer programs. If the transponder or receiver is WiFi enabled, you are able to use your smart phone, tablet or computer as an AIS display.

AIS Aerial/Splitter: A dedicated AIS aerial is used to pick up and transmit AIS signals only. A AIS/VHF splitter can be installed in order to share an existing VHF aerial between your VHF radio and AIS transponder or receiver.

AIS transponders are required on all ships over 300 tons when operating internationally and 500 tons when operating domestically. Passenger ships are required regardless of their destination. This means that nearly every commercial vessel will have one. In addition, many yachts and other vessels voluntarily carry an AIS transponder. Each year more and more vessels are equipped with AIS because of the significant safety benefits.

AIS data is transmitted from vessels at a variety of rates. Class A ships send position updates every 2 - 10 seconds depending on their speed and rate of turn, or every 3 minutes when reporting as anchored/moored and not moving faster than 3 knots. Class B ships send position reports every 30 seconds when moving faster than 2 knots, otherwise it drops back to every 3 minutes. Information that doesn't change frequently, such as the vessel's name, size and voyage information, is sent every 6 minutes for both Class A and B.

How AIS works:

Each AIS system consists of one VHF transmitter, two VHF TDMA receivers, one VHF DSC receiver, and standard marine electronic communications links (IEC 61162/NMEA 0183) to shipboard display and sensor systems (AIS Schematic). Position and timing information is normally derived from an integral or external global navigation satellite system (e.g. GPS) receiver, including a medium frequency differential GNSS receiver for precise position in coastal and inland waters. Other information broadcast by the AIS, if available, is electronically obtained from shipboard equipment through standard marine data connections. Heading information and course and speed over ground would normally be provided by all AIS-equipped ships. Other information, such as rate of turn, angle of heel, pitch and roll, and destination and ETA could also be provided.

AIS normally works in an autonomous and continuous mode, regardless of whether it is operating in the open seas or coastal or inland areas. Transmissions use 9.6 kb GMSK FM modulation over 25 or 12.5 kHz channels using HDLC packet protocols. Although only one radio channel is necessary, each station transmits and receives over two radio channels to avoid interference problems, and to allow channels to be shifted without communications loss from other ships. The system provides for automatic contention resolution between itself and other stations, and communications integrity is maintained even in overload situations.

Each station determines its own transmission schedule (slot), based upon data link traffic history and knowledge of future actions by other stations. A position report from one AIS station fits into one of 2250 time slots established every 60 seconds. AIS stations continuously synchronize themselves to each other, to avoid overlap of slot transmissions. Slot selection by an AIS station is randomized within a defined interval, and tagged with a random timeout of between 0 and 8 frames. When a station changes its slot assignment, it pre-announces both the new location and the timeout for that location. In this way new stations, including those stations which suddenly come within radio range close to other vessels, will always be received by those vessels.

The benefits of AIS...

Operating in the VHF maritime band, the AIS (Automatic Identification System) system enables the wireless exchange of navigation status between vessels and shore-side traffic monitoring centers. Commercial ships, ocean-going vessels and recreational boats equipped with AIS transceivers broadcast AIS messages that include the vessel's name, course, speed and current navigation status.

  • Transmit your position. Fitting a Class A or Class B AIS transceiver ensures that you are seen by other AIS equipped vessels.
  • Vessel Protection. As part of a suitably configured network, AIS enables owners to be alerted to unauthorized vessel movements.
  • Port management. AIS can be used as a highly effective port management tool allowing easy identification, control and direction of vessels.
  • Coastal surveillance. AIS and radar can be fused to create effective and efficient coastal tracking, surveillance and safety systems.

The Class A receiver and transmitter is approved to deep sea and inland waterway standards and offers a highly intuitive user interface.

The class B AIS transceiver allow you to transmit your data to other AIS equipped vessels, and receive their data for viewing right on your multifunction display's radar or chartplotter screen

AIS Requirements:

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, as follows:

  • Ships constructed on or after 1 July 2002
  • Ships engaged on international voyages constructed before 1 July 2002
  • In the case of passenger ships, not later than 1 July 2003
  • In the case of tankers, not later than the first "safety equipment survey" after 1 July 2003
  • In the case of ships, other than passenger ships and tankers, of 50,000 gross tonnage and upwards, not later than 1 July 2004
  • In the case of ships, other than passenger ships and tankers, of 10,000 gross tonnage and upwards but less than 50,000 gross tonnage, not later than 1 July 2005
  • In the case of ships, other than passenger ships and tankers, of 3,000 gross tonnage and upwards but less than 10,000 gross tonnage, not later than 1 July 2006
  • In the case of ships, other than passenger ships and tankers, of 300 gross tonnage and upwards but less than 3,000 gross tonnage, not later than 1 July 2007

The United States Coast Guard also requires AIS on certain vessels not subject to SOLAS under new USCG rules which take effect March 2016.