The main limitations are incomplete carriage, switch-off, gaps, errors, manipulation, and over-reliance on AIS data.
Shipborne AIS information is divided into static data, automatically sensor-updated dynamic data apart from manually entered navigational status, and manually maintained voyage-related data. Not all ships carry AIS, fitted units may be switched off in limited safety or security circumstances, and received data may be incomplete, unavailable or wrong. A typical ship-to-ship AIS range at sea is stated by IMO as 20 to 30 nautical miles depending on antenna height, but terrain, stations and radio conditions prevent a guaranteed universal range.
The built-in integrity test can report equipment malfunction but does not validate the accuracy of connected sensor data; routine checks and corroboration remain necessary. UK OFSI guidance defines AIS spoofing as manipulation of AIS data that can broadcast different identifying information, conceal voyage information or mask vessel movement; this is distinct from ordinary error, poor transmission or legitimate disablement. AIS does not prevent collisions by itself and does not replace visual lookout, radar plotting, use of all available means or compliance with the COLREG.
