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 are 161.975 and 162.025 MHz. A comprehensive explanation can be found on the site of the U.S. Coast Guard.

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)

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 with navigation software like SeaClear or
WinGPS. This requires somewhat more computer
knowledge to configure.

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.

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.

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. A good choice is www.vesseltracker.com.

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 Jul 2010 00:31 CEST

To monitor the performance of your system and to compare different receivers or antennas, you can use ShipPlotter.xls. This Excel-file, programmed by Neal Arundale, is run from the same directory containing shipplotter.exe.

It shows the number of ships in range and AIS messages received per minute (left vertical axis) and the reception range (right vertical axis).

For a reliable overview of most European and worldwide ports, I recommend www.vesseltracker.com. Apart from a detailed overview of shipping traffic, Vesseltracker offers historical data and photo's of individual vessels.