Frequently Asked Questions

What information is broadcast?

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
  • Call sign
  • Ship's name
  • Type of ship
  • Width, length and draught
  • Antenna Location
  • Destination
  • Estimated time of arrival (ETA)

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

The AIS signal is broadcast on alternate frequencies (Marine VHF band: 161.975 and 162.025 MHz) so if a receiver is only listening on one channel, it may take twice as long to pick up this information. This isn't significant at close range where there is a good signal, but at long range where