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AIS (Automatic Identification System)

AIS is a transponder system for ships intending to increase the safety at sea. It operates in the VHF band. The two frequencies used worldwide are 161.975 and 162.025 MHz (channels 87B and 88B, or AIS1 and AIS2).

An AIS transmitter regularly transmits the ship's position, heading, speed and MMSI (the unique maritime identification number). This data is received by ships in the vicinity. The data can be plotted automatically on a digital map or radar screen.


Every 2 - 10 seconds, a ship equipped with AIS e.g. transmits the following data:

  • MMSI number
  • Navigation status, e.g. 'at anchor' or 'under way'
  • Ground speed, from 0 to 102 kts in steps of 0,1 kt
  • Rate of turn, 0 to 720 degrees per minute
  • Position
  • Heading and Course over Ground
  • Time stamp
Furthermore, every six minutes the following information is transmitted:
  • MMSI number
  • Callsign
  • Ship's name
  • Type of ship or cargo
  • Dimensions of the ship
  • Draught, 0.1 to 25.5 m
  • Destination
  • Estimated time of arrival (ETA) at destination (captain's discretion)

Ships broadcast all information alternating between the two channels.

To receive AIS, there are several options:

Option 1: PC with soundcard

You'll need
  • A receiver with a discriminator output or 9600 bps packet radio output
  • An audio cable between your receiver and PC
  • A PC with soundcard, runningthe appropriate software:
    - Shipplotter, a complete solution. Or
    - AISMon, which converts the raw AIS signal into
      NMEA, together with with navigation software like
      SeaClear, OpenCPN or WinGPS, or a chart plotter.
      This requires somewhat more computer knowledge
      to configure.
AIS reception with a PC

Be advised that your receiver should not be scanning when you want to receive AIS, since it would miss AIS transmissions (hence ships) while scanning other frequencies. Tune your radio to either one AIS frequency.

If you use a marine VHF, it should be on channel 87 or 88 constantly. Since it can't be used for normal traffic while monitoring AIS, it is advisable to use a (cheap) scanner or a second marine VHF for AIS. Further to that, not all marine VHF equipment is suited to receive AIS.

Option 2: PC with serial port

You'll need
  • A dedicated AIS receiver, like the NASA AIS Engine or the SR161/SR162. These receivers contain a microprocessor that translates the raw AIS signal into NMEA sentences
  • A PC with a serial port, running navigation software to process the NMEA sentences, or an AIS plotter
This (more expensive) option is out of scope for this website, which focuses on using a (cheap) scanner or marine VHF.

AIS reception with a PC
The interfaces on this site are meant for paging. They can't be used for AIS.

Option 3: Internet

You're far from the nearest port or the coast? Or you don't want to do it yourself? Several internet sites offer AIS information.

Left, you see a recent image that I received on the east side of Rotterdam. Click on the image to get a full-sceen version. The time shown top left is UTC.

If you registered Shipplotter, you can see what other people receive by selecting the "Sharing' option, while other people can see the ships that you receive.

Rotterdam, 31 Dec 2023 20:25 CET

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