The Truth About AIS (Automatic Identification Systems)
Automatic Identification System (AIS) Class A AIS transponders are now a mandatory fit on all commercial vessels over 300 tonnes and on most passenger carrying vessels. Many leisure users embrace AIS technology thanks to low cost Class B transponders and even ‘receive only’ systems which allow an overview of AIS targets within range on a chart plotter or radar based system. It is probably fair to say that AIS has made the biggest step change in marine navigation safety since GPS became common place and affordable over a quarter of a century ago.
Whilst AIS is not a substitute for radar, the benefits of AIS using VHF communication frequencies allow it to see around headlands and to also positively identify an AIS equipped vessel. It also establishes the vessel’s name, call sign, current course and speed, making inter ship communication even easier and assists in making anti-collision calculations based on accurate closest point of approach (CPA) and time to CPA (TCPA) data.
Like any new technology, a few myths have crept into circulation which needs some explanation. The most common is that Class A systems can’t see Class B targets. That’s not true, but some of the very early Class A transponder systems did not have the correct software to decode the Class B format in its entirety. Class B transponders use a specific message format which incorporates the static data about the vessel such as name and MMSI number. Whilst the Class A transponders could see the Class B target, no static data was available as they did not decode this message properly. Most products have now had software upgrades and, of course, all the modern Class A products support interoperability between the two data standards. Even some leisure chart plotter products did not correctly decode this information so it is worth checking with your plotter manufacturer to see if there is a more recent update.
AIS is also becoming more ubiquitous in other systems such as Man Overboard devices (MOB) and security systems. McMurdo & Kannad have now introduced two new portable AIS transponders which effectively allow the use of AIS as a MOB device. Any vessel equipped with an AIS receiver or transponder can pick up these transmissions to quickly locate their missing crew and instantly establish bearing and distance back to the MOB position – all updated in real time. Even the Kannad life jacket fitted transponder units are showing a range of up to about four miles and German company, Weatherdock, have already launched an Easy AIS SART designed for personal use. Digital Yacht has already updated the functionality of their SmarterTrack PC software to allow correct decoding of these AIS SART messages to accurately show a MOB position on the chart overlay. More and more dedicated chart plotter manufactures are starting to play ‘catch up’ and this will be an important area for the future. The Volvo Round the World race boats also chose Digital Yacht AIT1000 transponders and Kannad AIS MOB devices to provide protection for their crew in the event of MOB.
Use of land based AIS base stations is also becoming popular with many services such as www.shipfinder.com providing internet-based vessel tracking thanks to a range of AIS enthusiasts and other base stations who provide a data feed from coast stations around the world. A great application here is vessel security where an AIS transponder could be left activated on board the boat even whilst moored. Owners can then keep a regular check on their boat and its whereabouts and charter companies can keep track of their fleet.
Not everyone wants to transmit all the time however. You may not want other users keeping track of your position – maybe when fishing or yacht racing or even when in pirate infested areas. Make sure that your transponder has an easy to use silence facility so that the transmission can be silenced and yet you can continue to take advantage of AIS reception.
For the future we will be seeing more and more satellite based AIS tracking systems to effectively give global tracking coverage on vessels equipped with AIS. There’s talk of AIS and satellite based MOB system being available in the short term, so AIS is definitely a technology that is here to stay and for tomorrow – and no doubt more and more uses will come to light over time.
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