What is AIS & How Does It Work?
With more and more leisure boats venturing further from their local shores, safety is paramount. Leisure boat users may be sailing in the same waters as large commercial vessels and will need to have their position and information noted to avoid any collision. This is what AIS (Automatic Identification System) does. How AIS Works:
AIS works by taking your position and movements via the vessels’ GPS system or an internal sensor built into an AIS unit. That information is then collated along with programmable information from the AIS unit (e.g. Maritime Mobile Service Identity (MMSI) number, vessel name, destination, cargo type) and is transmitted in the background at regular intervals whilst also receiving other vessels AIS information. The AIS unit can have its own separate antenna or an antenna splitter can be used from the antenna the VHF radio transmits from. If an antenna splitter is used, it must be an active splitter suitable for a VHF radio and AIS transponder. AIS information provides an overview of every large and potential hazard transmitting via AIS relative to your own vessels’ position. This will be displayed either on a chart plotter showing the positions of the other vessels or on a radar display. Depending on the type of chart plotter or display you are using, you can have the option to select the other vessels information to view their MMSI number and call them directly through the VHF radio. Shore based stations also have equipment that receive AIS transmitted information and display it on an electronic chart showing ‘traffic’ within the waters near them. These stations can monitor the vessels and provide added safety as they have the ability to call ships directly and warn them of potential hazards. AIS Classification:
There are 2 types of AIS classes used by ships, Class-A and Class-B. Class-A:
This class is used by commercial ships and they operate on 12 watts while transmitting their information typically every 2 to 12 seconds (depending on speed or if at anchor) with a range of 20 miles or more if the right antenna is fitted high enough. * Class-B:
This class is used mainly by leisure boaters and operates at a lower 2 watts, broadcasting less frequently (roughly 30 seconds) and has a range of 5 to 6 miles. *
* Transmit range only. Receiving range will vary.
Type of information transmitted:
AIS transponders typically transmit the following information: • Vessel name, MMSI number and call sign
• Type of vessel (such as passenger, cargo, fishing)
• Vessel’s position (current latitude and longitude)
• Course over ground (COG)
• Speed over ground (SOG)
• Heading from your vessel
• Closest point of approach (CPA) (distance)
• Time to closest point of approach (TCPA)
• Vessels’ dimensions (length, beam and draught) Please note, type of information transmitted may differ from Class-A and Class-B transponders. Other Uses For AIS:
AIS has uses other than just for collision prevention. Fishing fleets can contact other vessels within their vicinity to warn of trailing fishing nets and suggest course corrections to avoid entanglement. AIS can be used in personal locator beacons for members of a ship’s crew. If a crew member was to fall overboard then a small transmitter worn by the crew would activate. Their boat or another vessel will then see the bearing and distance to the person in the water as the AIS information will be displayed on their navigational equipment. Also, anyone can track ships via AIS on the internet via such sites like http:/www.marinetraffic.com. On a commercial side, ship managers can track their fleet of ships when at sea. On a leisure side, a relative or friend of a person who is sailing could arrange to meet up at a port or marina close to their current position or just check on their progress.