Marine AIS typically reaches 20 to 30 nautical miles between ships, though no universal distance is guaranteed.
AIS is a cooperative VHF data system through which equipped ships and shore facilities automatically exchange identity, position, course, speed, navigational status and other safety-related information. This 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.
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. Consequently, the actual reach varies significantly based on equipment class, motion, geography and reception quality rather than a fixed standard.
