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WHAT AIS BROADCASTS

A Class A AIS unit broadcasts the following information every 2 to 10 seconds while underway, and every 3 minutes while at anchor at a power level of 12.5 watts. The information broadcast includes:

  • MMSI number - unique referenceable identification
  • Navigation status (as defined by the COLREGS - not only are "at anchor" and "under way using engine" currently defined, but "not under command" is also currently defined)
  • Rate of turn - right or left, 0 to 720 degrees per minute (input from rate-of-turn indicator)
  • Speed over ground - 1/10 knot resolution from 0 to 102 knots
  • Position accuracy - differential GPS or other and an indication if (Receiver Autonomous Integrity Monitoring) RAIM processing is being used 
  • Longitude - to 1/10000 minute and Latitude - to 1/10000 minute
  • Course over ground - relative to true north to 1/10th degree
  • True Heading - 0 to 359 degrees derived from gyro input
  • Time stamp - The universal time to nearest second that this information was generated

In addition, the Class A AIS unit broadcasts the following information every 6 minutes:

  • MMSI number - same unique identification used above, links the data above to described vessel
  • IMO number - unique referenceable identification (related to ship's construction)
  • Radio call sign - international call sign assigned to vessel, often used on voice radio
  • Name - Name of ship, 20 characters are provided
  • Type of ship/cargo - there is a table of possibilities that are available
  • Dimensions of ship - to nearest meter
  • Location on ship where reference point for position reports is located
  • Type of position fixing device - various options from differential GPS to undefined
  • Draught of ship - 1/10 meter to 25.5 meters [note "air-draught" is not provided]
  • Destination - 20 characters are provided
  • Estimated time of Arrival at destination - month, day, hour, and minute in UTC