Automatic Identification System: how it works and what it looks like on a ship's display. Tap any target to see what it is sending.
Tap a target on the display to see what it sends.
AIS is an automatic tracking system on VHF. Every AIS-equipped ship keeps broadcasting who it is, where it is and where it is going, and receives the same from every ship around it. Nobody has to press anything or speak on the radio.
The ship's AIS display, chart plotter, ECDIS or radar overlay turns those messages into targets on the screen, so you can see a ship's name and course before you can even see it by eye. Its main job is collision avoidance and traffic monitoring by shore stations.
Set once when the AIS is installed.
From the ship's GPS and compass, updated all the time.
Typed in by the crew for each trip.
How often it reports depends on what it's doing: every 2 to 10 seconds underway (faster when it's fast or turning), and every 3 minutes at anchor.
| Class A | Class B | |
|---|---|---|
| Who fits it | Commercial ships (required by SOLAS) | Yachts and small craft |
| Power | 12.5 W | 2–5 W |
| Range | About 20–30 NM | About 10–15 NM, line of sight |
| Power supply | Ship's mains power: no emergency battery | |
Every AIS target has a 9-digit MMSI. The first digits tell you what kind of station it is.
| Ship | 428 123 456 | Starts with the country code (MID). 428 = Israel |
|---|---|---|
| Coast station | 004 281 234 | 00 + MID |
| SAR aircraft | 111 428 123 | 111 + MID |
| Nav aid | 994 281 234 | 99 + MID |
| AIS-SART | 970 721 234 | 970, no MID |
| MOB device | 972 721 234 | 972, no MID |
| AIS-EPIRB | 974 721 234 | 974, no MID |
Memory hook for the 97x devices: 0 = SART, 2 = MOB, 4 = EPIRB.
AIS-SARTs, MOB devices and AIS-EPIRBs use the same AIS channels to put survivors on every nearby ship's screen. They show as a circle with a cross and set off an alarm with a message like SART ACTIVE or EPIRB ACTIVE, plus their exact GPS position. In a self-test you see SART TEST or EPIRB TEST instead.