How useful is AIS?

There are some caveats around the use of AIS. These are neatly summarised by the following extract from Merchant Shipping Notice MSN1795, issued by the MCA. The potential of AIS as an anti-collision device is recognised and AIS may be recommended as such a device in due time. Nevertheless, AIS information may be used to assist collision avoidance decision making. When using the AIS in the ship-to-ship mode for anti-collision purposes, the following precautionary points should be borne in mind: ■ AIS is an additional source of navigational information. It does not replace, but supports, navigational systems such as radar target tracking and VTS; and the use of AIS does not negate the responsibility of the OOW to comply at all times with the COLREGS. ■ The user should not rely on AIS as the sole information system, but should make use of all safety-relevant information available. ■ The use of AIS on board ship is not intended to have any special impact on the composition of the navigational watch, which should be determined in accordance with the STCW Convention. ■ Once a ship has been detected, AIS can assist tracking it as a target. By monitoring the information broadcast by that target, its actions can also be monitored. Changes in heading and course are, for example, immediately apparent, and many of the problems common to tracking targets by radar, namely clutter, target swap as ships pass close by and target loss following a fast manoeuvre, do not affect AIS. AIS can also assist in the identification of targets, by name or call sign and by ship type and navigational status. Installing an AIS transponder won’t act as a complete ‘ship repellent’ and keep big ships away from you – it’s still best to stay on your guard. But what it will do is add another level to the other precautions we take – radar reflectors, nav lights, etc – and increase the possibility that you’ll be seen.