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AIS Information

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What is AIS?

AIS stands for Automatic Identification System (AIS)

The Automatic Identification System (AIS) is a maritime transponder/reciever system defined by the IMO.( international maritime organisation) AIS operates in the VHF frequency band. The main objectives of AIS are:

  • to improve maritime safety

  • to protect the maritime environment

  • Practically the AIS:

  • assists collision avoidance (AIS ship-to-ship)

  • enables ports and coastal states to identify ships and to managesand supervise the traffic in their waters (AIS Coast station).


Description:


AIS is a system used by ships and vessels for identification at sea. AIS helps to resolve the difficulty of identifying ships when not in sight (e.g. at night, in radar blind arcs or shadows or at distance) by providing ID, position, course, speed and other ship data to all other nearby ships and VTS stations. The IMO SOLAS requires AIS to be fitted aboard all ships of gross tonnage >= 300 for international voyages. The ship datas are displayed on a AIS data capable chartplotter with an ship symbol or even on AIS data capable navigation software.

AIS transponders automatically transmit the position and velocity of the ship at regular intervals via a  VHF radio built into the AIS. The position and velocity originate from the ship's GPS or, if that fails, from an integral GPS receiver. The AIS also receives heading information from the ship's compass and transmits this at the same time. Other information, such as the vessel name and VHF call sign, is entered when installing the equipment and is transmitted less frequently. The signals are received by AIS transponders fitted on other ships or on land based systems, such as VTS systems.

In order to ensure that the VHF transmisions of different AIS transponders do not occur at the same time they are time multiplexed. In order to make the most efficient use of the bandwidth available, vessels which are anchored or are moving slowly transmit less frequently than those that are moving faster or are manoeuvering. The update rate of fast manoeuvering vessels is similar to that of a conventional marine radar.

AIS transponders automatically transmit the position and velocity of the ship at regular intervals via a VHF radio built into the AIS. The position and velocity originate from the ship's GPS or, if that fails, from an integral GPS receiver. The AIS also receives destination information from the ship's compass and transmits this at the same time. Other information, such as the vessel name and VHF call sign, is entered when installing the equipment and is transmitted less frequently. The signals are received by AIS transponders fitted on other ships or on land based systems, such as VTS systems. In order to ensure that the VHF transmisions of different AIS transponders do not occur at the same time they are time multiplexed. In order to make the most efficient use of the bandwidth available, vessels which are anchored or are moving slowly transmit less frequently than those that are moving faster or are manoeuvering. The update rate of fast manoeuvering vessels is similar to that of a conventional marine radar.

AIS Class A transceiver sends the following data every 2 to 10 seconds depending on vessels speed while underway, and every 3 minutes while vessel is at anchor.

Three Types of Marine AIS Equipment Available

Currently, there are three different types of marine AIS equipment:

Class A transponders,
Class B transponders, and
AIS receivers.

Class A transponders are intended for commercial ships, and meet International Marine Organization (IMO) and SOLAS (Safety of Life at Sea) regulatory requirements. They retail for more than $4,000.

Class B transponders, meanwhile, are aimed at recreational boaters and yachts, although the Coast Guard eventually may allow some smaller commercial ships to carry them. They retail for between $750 and $1,500, depending on brand, model and features.

Finally, AIS receivers will receive and display information about other vessels, but do not transmit data, which means their owners can see other ships but those ships can't see them.

This data includeed in a transmitted telegram :

MMSI number of vessel - vessel's unique identification (Transmitted by Class A and Class B)
Navigation status - "at anchor", "under way using engine" or "not under command" (Transmitted by Class A and Class B)
Rate of turn - right or left, 0 to 720 degrees per minute (Transmitted by Class A )
Speed over ground - 0.1 knot resolution from 0 to 102 knots (Transmitted by Class A and Class B)
Position accuracy (Transmitted by Class A)
Longitude - to 1/10000 minute and Latitude - to 1/10000 minute (Transmitted by Class A and Class B)
Course over ground - relative to true north to 0.1 degree (Transmitted by Class A and Class B)
True Heading - 0 to 359 degrees from eg. gyro compass (Transmitted by Class A)
Time stamp - UTC time accurate to nearest second when this data was generated (Transmitted by Class A and Class B)
Not all of above data is displayed (Quantity of shown data is software of the Chartplotter).

Typically you can see following data on the chartplotter:

Depending on type of transmitter and speed the following dynamic data are transmitted:

MMSI number of vessel - vessel's unique identification
Speed over ground - 0.1 knot resolution from 0 to 102 knots
Course over ground - relative to true north to 0.1 degree

In addition, the following static data are broadcast every 6 minutes:

MMSI number - vessel's unique identification (Transmitted by Class A and Class B)
IMO number (Transmitted by Class A and Class B)
Radio call sign - international radio call sign assigned to vessel (Transmitted by Class A and Class B)
Name - Name of vessel, max 20 characters (Transmitted by Class A and Class B)
Type of ship/cargo (Transmitted by Class A and Class B)
Dimensions of ship - to nearest meter (Transmitted by Class A and Class B)
Location of positioning system's (eg. GPS) antenna onboard the vessel (Transmitted by Class A)
Draught of ship - 0.1 meter to 25.5 meters (Transmitted by Class A)
Destination - max 20 characters (Transmitted by Class A )
ETA (estimated time of arrival) at destination - UTC month/date hour:minute (Transmitted by Class A)

The AIS has been  mandatory since 2002 for commercial ships constructed on or after July 2002. It is already fully effective for passenger ships and tankers constructed before July 2002 engaged on international voyages. End of July 2004, it will be mandatory for all cargo ships 50,000 gt engaged on international voyages. It will be adopted by all ships of 300 gt and upwards engaged on international voyages or not, in 2008.

The information provided above is not complete and should only be an overview regarding AIS. For more details please have a look at the following links :


http://www.navcen.uscg.gov
http://www.imo.org

 
 
 
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