| By "clicking" on a ship mark, you could learn the ship name, course and speed, classification, call sign, registration number, MMSI, and other information. Maneuvering information, closest point of approach (CPA), time to closest point of approach (TCPA) and other navigation information, more accurate and more timely than information available from an automatic radar plotting aid, could also be available. Display information previously available only to modern Vessel Traffic Service operations centers could now be available to every AIS-equipped ship.
With this information, you could call any ship over VHF radiotelephone by name, rather than by "ship off my port bow" or some other imprecise means. Or you could dial it up directly using GMDSS equipment. Or you could send to the ship, or receive from it, short safety-related email messages.
The AIS [47 CFR 80.5, AIS Definition] is a shipboard broadcast system that acts like a transponder, operating in the VHF maritime band, that is capable of handling well over 4,500 reports per minute and updates as often as every two seconds. Shipboard AIS devices use either Self-Organizing Time Division Multiple Access (SOTDMA) or Carrier-Sense Time Division Multiple Access (CSTDMA) technology.
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. It will continue transmitting even if position information is lost. 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
AIS Base stations
- MMSI number
- UTC year, month, day. hour, second
- Longitude - to 1/10000 minute and Latitude - to 1/10000 minute
- Position accuracy - differential GPS or other and an indication if (Receiver Autonomous Integrity Monitoring) RAIM processing is being used
- Channel management**
- Safety related message (addressed or broadcast)**
- Binary message (addressed or broadcast)**
- Assignment mode command**
- DGPS messages per ITU-R Rec. M.823**
- Data link management message**
- Group assignment command**
AIS Aids to Navigation stations
- MMSI number
- Type of aids to navigation
- Name of aid to navigation (20 or more characters)
- 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
- Dimension/reference for position
- Type of electronic position fixing device
- Time stamp
- Off position indicator
- AtoN status
- Virtual AtoN flag
Search and Rescue Aircraft
- MMSI number
- Altitude
- Speed over ground
- Course over ground
- 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
- Altitude sensor (GNSS or barometric)
Search and Rescue Transmitter
An AIS SART transmits Message 1 “Position Report” with the Navigational Status set to
“15 = not defined" and Message 14 Safety Related Message with the text “SART
ACTIVE”. When the AIS SART is tested, the device transmits the text "SART under test" on AIS1 and the "SART test finished" on AIS 2.
* Information broadcast by Class B devices. Note Class B also transmits unique identification of a unit as defines by the manufacturer, information not broadcast by Class A devices.
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