The AIS system is a shipboard broadcast system that operates in the VHF maritime band, capable of handling well over 4,500 reports per minute and updating every two seconds. It acts like a continuous, autonomous transponder. AIS allows ships and boats to easily track, identify and exchange pertinent navigation information to one another or ashore; for collision avoidance, VTS reporting, and security.
The following commercial domestic vessels must have an installed operational AIS that complies with the standards adopted internationally and approved by the Coast Guard for such devices.
- Each self-propelled commercial and fishing vessel of 65 feet or more in length
- Each passenger vessel certificated to carry 50 or more passengers for hire
- Each vessel of 100 gross tons or more carrying one or more passengers for hire
- Each towing vessel of 26 feet or more in length and more than 600 horsepower
In addition to the AIS system’s primary role of preventing vessel collisions, AIS has also been a key factor in assisting the Coast Guard with a variety of missions including search and rescue, Maritime Domain Awareness, a means to obtain information about a ship and its cargo, and maritime security.
Each Vessel’s AIS transmits a signal through a transponder, which broadcasts its information in intervals. The broadcast includes information such as the vessels name, call sign, Maritime Mobile Service Identity (MMSI) number, position, speed, and navigation information. This information is commonly displayed on either a computer screen found in Coast Guard Command Centers, or on a screen similar to a radar display on board vessels.
In an effort to closely monitor vessel traffic, Coast Guard Sector Command Centers and all Coast Guard sea-going vessels are equipped with AIS monitoring systems. The Coast Guard, in our efforts to ensure the safety and security of the nation, mans a 24 hour a day, 365 days a year watch in these Command Centers and remains constantly vigilant of incoming and outgoing vessels.
AIS serves as a valuable tool and allows the Coast Guard to screen vessel traffic and communicate with commercial shipping and large passenger vessels to help avoid collisions. There are two major types of AIS, Class A and Class B. Class A, the more expensive of the two, is used on larger vessels that are often required to carry AIS by law. Class B AIS units are more often used on yachts and sailing vessels. Class A units are capable of broadcasting a wide variety of information, including course, position, turn rate, MMSI number, destination and type of cargo. Class B units are nearly identical to Class A units, but are limited by the amount of data they can transmit. Class B units transmit every 30 seconds, while Class A units transmit more information every 2 to 10 seconds.
According to Regulation 18 of Safety of Life At Sea, all vessels over 300 gross tons engaged on international voyages, vessels 500 gross tonnage and upwards not engaged on international voyages, and all passenger ships irrespective of size are required to equip an AIS Class A system. Ships fitted with AIS shall maintain AIS in operation at all times except where international agreements, rules or standards provide for the protection of navigational information. ✦