Automatic Identification System (AIS)
A VHF-based system that automatically exchanges vessel identity, position and movement data.
Commonly abbreviated to AIS, it transmits dynamic information such as position, course and speed together with entered or programmed information such as identity, vessel type and voyage details. Compatible vessels, shore stations and aids to navigation can receive and display those reports.
AIS supports traffic awareness and can assist collision-risk assessment, but reports may be delayed, incorrect, incomplete or absent. Not every vessel carries or transmits AIS, antenna and radio coverage are limited, and entered data may be wrong. It must therefore be used with lookout, radar where fitted and all other available information.
Class A and Class B equipment differ in capability, reporting behaviour and carriage application, with further variations within Class B. The installed unit’s specification and current regulatory requirements should be consulted rather than assuming one fixed update interval or range.
