A SART is an emergency transponder designed to be used in distress situations at sea. It is typically a self-contained and waterproof device that can be either a radar-SART or a GPS-based AIS-SART. A radar-SART functions by producing a series of dots on a rescuing ship’s radar display to help locate a survival craft or a vessel in distress.
It can only respond to a 9 GHz X-band radar and is not visible on other radars. On the other hand, a GPS-based AIS-SART utilizes the Automatic Identification System to provide the vessel’s identification, position, and other vital information to the rescuing ship.
SARTs are mandatory safety devices on board vessels as per the Global Maritime Distress Safety System (GMDSS). All vessels up to 500 GRT must carry at least one SART, while vessels exceeding 500 GRT must have at least two.
The device is designed to transmit a signal as soon as it detects the radar signal from a nearby ship. The radar signal is detected by the SART’s receiver, which then transmits twelve pulses at the same frequency.
These pulses appear on the rescuing ship’s radar screen as a series of twelve dots with a gap of 0.6 miles between them, with the first dot representing the SART’s position and the others extending in a straight line toward the edge of the screen.
As the rescuing vessel approaches the SART’s location, the dots on the radar display transform into short arcs, which increase in size as the vessel gets closer.
Once the rescue vessel is in close proximity, the side lobes of the radar antenna activate the SART permanently, and the twelve dots will appear as complete circles on the radar screen, indicating to the search-and-rescue team that they have reached the SART’s location.
Overall, SARTs play a critical role in maritime safety by helping to quickly locate and rescue vessels and individuals in distress.