Module 9 — SART, AIS-SART and survival VHF

A radar SART responds to suitable X-band radar and creates twelve marks extending away from its approximate position; arcs or circles can appear at close range. AIS-SART broadcasts locating information on AIS frequencies, with identity prefix 970. They locate survivors and complement the EPIRB alerting function.

Radar SART endurance is 96 h standby followed by 8 h continuous interrogation; AIS-SART requires 96 h operation. Raise the antenna to at least 1 m above sea level as instructed. Radar settings and equipment compatibility affect detection. Transfer the devices assigned by the muster plan to survival craft when safe. A survival-craft portable VHF provides channel 16 and at least one additional channel; use approved emergency batteries and testing procedures.

Two locating devices, two detection pictures

Once the alert is out, the rescuers' problem changes from "is someone in trouble?" to "where exactly is the liferaft?". An EPIRB position may be accurate to around a hundred metres, or a few miles off if it has no GNSS, and a liferaft drifts. SARTs solve the last few miles.

A radar SART responds when interrogated by a suitable X-band radar. It stays silent until a 9 GHz radar pulse hits it, then answers with a sweep that appears on the searching radar as a line of 12 dots running outward along the SART's bearing. The dots are about 0.6 NM apart, so the line stretches roughly 7 NM beyond the raft. The dot nearest the searcher marks the SART. Within about a mile the dots become arcs, and very close they turn into full circles. That tells the searcher they are almost there.

An AIS-SART works differently: it uses its own GNSS and broadcasts its position on the AIS channels about once a minute. It uses the identity prefix 970, so it appears on AIS displays, ECDIS and chart plotters as a special SAR symbol at its exact position.

Height is range

Both devices work by line of sight, and the sea surface gets in the way. A SART lying on the floor of a liferaft sits about 0.3 m above the water; in a 2 m swell it spends much of its time hidden in the troughs and behind the canopy. On the pole supplied, 1 m or more above the sea, it clears most waves and its range can roughly double. Mount it, hold it upright and keep it clear of the canopy.

A practical survival workflow

1. 1Follow the muster list: the person assigned takes the SART or AIS-SART and the survival-craft VHF.
2. 2Once in the raft, switch the SART on and fit it to its pole as high as you can.
3. 3Watch for the light or beep that shows a radar has interrogated it: a searcher is within range.
4. 4Listen on the survival VHF (Channel 16, with at least one other simplex channel, typically Channel 6) and tell rescuers what you have.
5. 5Save batteries: the survival VHF's sealed battery is rated for about 8 hours of use.

Worked insight: twelve marks are not twelve survivors

A watchkeeper sees 12 marks in a line on bearing 040°, the nearest at 4.2 NM. They are not 12 boats, and not range rings. They are one SART answering one radar. Steer for the inner dot at 4.2 NM. As you close, expect arcs at around a mile and circles very close. If AIS shows nothing at the same time, that does not disprove the SART: the raft may simply have no AIS-SART.

The IMO performance standards for radar SART and AIS-SART set the minimum figures; the device manual gives the switch-on, test and battery details for the unit on board.

In a drill, go through the three in that order: alert the rescue system, make the raft easy to find, then listen and answer.

Official references · 2026-09-09

MSC.510(105) · MSC.246(83)