AIS is a VHF-based transponder system that automatically broadcasts and receives vessel identification and navigation data between ships and shore stations, without requiring active operator input for each transmission.
What AIS Broadcasts
- Static data: vessel name, IMO number, call sign, dimensions
- Dynamic data: position, course, speed, heading, rate of turn — updated automatically every few seconds to minutes depending on vessel speed
- Voyage data: destination, ETA, draft, cargo type (as entered by the crew)
Why It Matters
- Collision avoidance — AIS provides identity and precise course/speed data that radar alone cannot, letting the bridge team know exactly which vessel is which in busy or congested waters
- Traffic monitoring — VTS (Vessel Traffic Service) stations and port authorities use AIS to monitor and coordinate vessel movement
- Search and rescue — AIS position data assists in locating vessels in distress
SOLAS Requirement
AIS is mandatory under SOLAS Chapter V for all passenger ships and cargo ships of 300 gross tonnage and above on international voyages, and cargo ships of 500 gross tonnage and above on domestic voyages.
Limitations
AIS depends on the transponder being switched on and correctly configured — it is a supplement to, not a replacement for, radar and visual lookout, since not every vessel (small craft, some fishing vessels) carries or activates it.
Exam Relevance
AIS operation, data interpretation, and its role alongside radar in collision avoidance are tested in both 2nd Mate FG and Master FG competency exams.