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
A radar SART responds when interrogated by a suitable X-band radar. On the radar display it produces a pattern of twelve marks extending from the approximate survivor position; at close range the pattern can appear as arcs or concentric circles. An AIS-SART instead broadcasts locating information on AIS frequencies and uses the identity prefix 970. Both devices help locate survivors and complement an EPIRB alert; neither replaces the other automatically.
Put the signal in the rescue team’s picture
Radar detection depends on a compatible radar, range, sea state, antenna height and line of sight. AIS-SART detection depends on an AIS receiver and the device’s transmission and antenna conditions. Raise the equipment as directed, keep it clear of obstructions and transfer assigned equipment to the survival craft when safe. A survival-craft portable VHF supports channel 16 and at least one additional channel under the applicable equipment standard.
| Device | What the rescuer sees |
|---|---|
| Radar SART | Twelve X-band radar responses, changing form at close range. |
| AIS-SART | AIS target data with identity prefix 970. |
| EPIRB | A satellite alert and locating information where supported. |
A practical survival workflow
- 1Follow the muster plan and take the assigned beacon, SART and portable VHF when safe.
- 2Activate the locating device using its marked procedure and confirm the antenna position.
- 3Keep the device exposed and monitor rescue instructions on the portable VHF.
- 4Tell rescuers which device is active and describe the expected radar or AIS presentation.
- 5Preserve batteries and follow approved test or replacement procedures after the event.
Worked insight: twelve marks are not twelve survivors
The radar SART pattern represents repeated radar responses from one approximate position. It is not a count of persons, boats or range rings. At close range the display geometry changes, so the watchkeeper must interpret the pattern with radar scale, bearing and visual information. An AIS-SART’s identity prefix helps recognition in an AIS display, but it still depends on a functioning AIS receiving picture and does not guarantee rescue contact.
The IMO performance standards for radar SART and AIS-SART should be paired with the actual device manual. Battery endurance, antenna height and exact indications are equipment-specific; check the approved values in the manual for the fitted device.
This separation makes the drill coherent: alert the rescue system, make the craft findable, then listen and respond.
Official references · 2026-09-09
Apply what you learned
A radar watch sees twelve marks spreading from a small craft’s bearing, while the AIS display shows no new target.
Which explanation fits the evidence?
Suggested answer: The pattern may be a radar SART; AIS absence does not disprove it.
Why this works: A radar SART responds to suitable X-band radar and produces twelve responses that may become arcs or circles nearby. An AIS-SART is a separate transmitter that requires an AIS receiving picture. The watchkeeper should verify radar compatibility, report the bearing and range, and use the survival VHF or other rescue communications to coordinate.
Continue with guided radio exercises.
Practise in the radio simulatorKey Takeaways
Radar SART responds to suitable X-band radar and shows a characteristic twelve-response pattern.
AIS-SART broadcasts locating data on AIS frequencies with identity prefix 970.
SARTs locate survivors and complement EPIRB alerting.
Detection depends on the matching receiver, exposure, antenna height and conditions.
Portable survival VHF supports the two-way coordination stage of the drill.
Common Mistakes
Expecting a radar SART to appear as an AIS target.
Counting twelve radar marks as twelve people or twelve range rings.
Hiding the antenna or relying on a locating device without monitoring rescue communications.
Test Your Knowledge
Practise this topic and review the explanation for each answer.
More GMDSS lessons
- Module 4 — MF/HF radiotelephony and DSCMF/HF DSC alerts and subsequent voice traffic use different frequencies.
- Module 5 — NBDP / radiotelexNBDP is narrow-band direct-printing telegraphy.
- Module 6 — Inmarsat C and EGCInmarsat-C provides data messaging, distress alerting and SafetyNET reception; it does not provide voice.
- Module 7 — NAVTEX and maritime safety informationInternational NAVTEX broadcasts on 518 kHz in English; national services may use 490 or 4209.5 kHz.
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