Automatic Identification of Ships (AIS)

AIS was introduced to assist the crew of a vessel in the identification of other vessels. In situations where it was necessary to call a nearby ship to avoid a collision, knowing the name of the nearby ship clearly helped to ensure that the correct vessel responded to the call. Previously, when just using an on board ARPA radar, calling a vessel using a phrase such as “vessel off my starboard bow” was not a guaranteed way of ensuring that the right message was received by the right vessel. The mandatory fitting of an AIS transponder to each SOLAS vessel means that every vessel transmits its ID and position at regular intervals. When integrated into the Bridge system of many ships, this provides an ID alongside the radar targets on the main ARPA and ECDIS displays and therefore enables the Officer on Watch to call a vessel by name.

For VTS and Coastal Surveillance, AIS enables all vessels within the Surveillance Area to be automatically identified. The AIS ID is displayed alongside the radar plot data and correlated with the extracted radar target data. AIS can provide much more information about the vessel, including its type, size, cargo and destination etc.. This information can be extremely useful in understanding the purpose of the voyage and more detailed information about the vessel itself to help ensure safe navigation. However, the additional information is all entered manually and therefore there are no guarantees that it has been entered correctly. Even the ships name is entered manually and there is no standard convention as to how it should be entered, or when. So if a ships name is changed, there is no guarantee that the AIS ships name will be updated on its AIS transponder.

Basestation or Transponder

For VTS systems (located onshore), the use of a mobile transponder (Class A or Class B) is not permitted. Mobile transponders are for use by ships. AIS Basestations or AIS Receivers can be used onshore. Most VTS Installations select an AIS Basestation as it has the ability to transmit its own position on every net cycle and will thereby appear on the ECDIS display of an approaching vessel. In addition, where a VTS system comprises a number of remote radar sites and therefore multiple AIS Basestations, all basestations can be set up with the same virtual MMSI so that the port only appears on the Ships ECDIS display in one location instead of identifying all of the sensor sites. AIS Basestations also provide additional functionality that could benefit VTS Operations, but is rarely set up and used. This includes being able to transmit text messages to ships and Aid to Navigation information to mark existing objects (using synthetic or virtual AtoNs) and the facilities to use binary messages for other value added functionality. An AIS Receiver may also be used onshore but only receives AIS information transmitted by ships.