Mersey View

Automatic Identification System

As part of the global maritime safety system, ships over 300 tons are now required to broadcast their positions using AIS.

A ship transmits "dynamic" information at intervals of between 2 and 12 seconds depending on the vessel's speed or 3 minutes if at anchor.

  • MMSI number
  • Navigation status, e.g. 'at anchor' or 'underway'
  • Ground speed, from 0 to 102 knots in steps of 0.1 knots
  • Rate of turn, 0 to 720 degrees per minute
  • Position (GPS latitude and longitude)
  • Heading and Course over Ground
  • Time stamp

Then every six minutes "static" information is transmitted:

  • MMSI number
  • Callsign
  • Ship's name
  • Type of ship (See AIS Type below)
  • Width, length and draught
  • Antenna Location
  • Destination
  • Estimated time of arrival (ETA)

Voyage related information such as draught, cargo, destination, ETA and route plan is generally manually entered and updated by the bridge team.

How do I receive this information?

Armed with:

  • A radio capable of receiving the Marine VHF band: 161.975 and 162.025 MHz with, preferably, an outdoor aerial. The receiver will need a discriminator output (see discriminator.nl) or alternatively, you can buy a dedicated AIS receiver eg This list is not a recommendation and there are many other receivers available). Have a look at the ShipPlotter FAQ
  • Pentium level PC running Win95/98/Me/2k/XP with compatible sound card.
  • The ShipPlotter program which can be downloaded and used for 21 days for free.
  • Some charts would be useful. These may be downloaded through the Yahoo ShipPlotter group or from my own satellite chart generator.

The output from the ShipPlotter program is saved into a MySQL database every 60 seconds. The results are then plotted using some home made PHP scripts. These scripts are available to anyone who would like to set up a similar website or build them into their own site.


Requirements for AIS

The eventual requirements for ships to carry AIS are:

  • All passenger ships.
  • All tankers.
  • Other ships of 300+ GT on international voyages.
  • Cargo ship of 500+ GT not on international voyages.
  • Ships constructed on or after July 1, 2002.

Passenger and tankers 50k+ GT already have to carry AIS. The timetable for implementation for ships other than tankers and passenger ships is

  1. 10k-50k GT by 1st July 2005
  2. 3k-10k GT by 1st July 2006
  3. 300-3000 GT by 1st July 2007
  4. Ships not on international voyage and built before 1st July 2002 by 1st July 2008.


AIS Type

With the detailed AIS information you will see a type description (eg Cargo) and a type number (70). The type number is what actually gets broadcast by AIS and this is converted to a description with the following formula:

The first digit represents the general category,

  1. Reserved
  2. Wing In Ground (See this footage on YouTube to see why you would want to get out of their way.)
  3. special category
  4. Hi Speed Craft
  5. special category
  6. Passenger
  7. Cargo
  8. Tanker
  9. Other

While the second digit gives some information as to the cargo

  1. Major Hazard (Haz A)
  2. Hazard (Haz B)
  3. Minor Hazard (Haz C)
  4. Recogniseable Hazard (Haz D)
  5. undefined
  6. undefined
  7. undefined
  8. undefined
  9. undefined

There are also special categories which start with 3 or 5

  1. Fishing
  2. Towing
  3. Towing
  4. Dredger
  5. Dive Vessel
  6. Military Operations
  7. Sailing
  8. Pleasure Craft
  9. Reserved
  10. Reserved
  1. Pilot Vessel
  2. Search and Rescue
  3. Tugs
  4. Port Tenders
  5. Anti-polution
  6. Law enforcement
  7. Local Vessel
  8. Local Vessel
  9. Medical Transport
  10. Special craft

As you can see, the types definitions are a bit vague and have gaps in. Also the operators are not always careful about filling in the numbers so occasionally you might see a ship with type 89. It's probably a tanker of some sort, but there's no definition as to what the 9 means. This is the reason for displaying the type number.