Search and Rescue Radar Transponder

The Search and Rescue Radar Transponder is a locating device designed to lead rescuers to a lifeboat or liferaft in the final stage of a search. It is a small, portable, battery-powered unit kept on the bridge or in the survival craft, and it works by responding to radar. When a searching ship or aircraft sweeps the area with its X-band (3 cm) radar, the SART detects the radar pulse and transmits a reply, which appears on the searcher's radar display as a line of twelve equally spaced blips extending outward from the SART's position along its bearing.

This radar signature is unmistakable and does two things at once: it tells the rescuers that survivors are present and it shows their exact bearing and range. As the searching unit closes in, the twelve dots widen into arcs and eventually into concentric circles centred on the SART, giving a clear, intuitive indication that the rescuer is almost on top of the survival craft. Because it relies on the searcher's own radar rather than on transmitting a signal continuously, a SART is simple, robust and effective precisely when it is needed.

The SART is part of the GMDSS suite of survival equipment and complements the EPIRB: where the EPIRB raises the alarm and gives a satellite-derived position to rescue authorities far away, the SART provides precise local homing for the vessels and aircraft that arrive to search. Ships carry SARTs according to their size and the number of survival craft, they are tested periodically, and their batteries have a defined service life. An alternative, the AIS-SART, performs the same locating role by transmitting the survivors' position as AIS messages that appear on nearby ships' AIS displays and ECDIS.