EPIRBs, SARTs and AIS-SARTs
What the exam tests here
Locating and alerting devices: how the 406 MHz EPIRB reaches the rescue services, and how the SART and AIS-SART let the rescuing ship or aircraft find the survival craft.
406 MHz EPIRB
A float-free satellite EPIRB transmits a digital alert on 406 MHz to the COSPAS-SARSAT system, which passes it through a Mission Control Centre to the responsible RCC. The message carries the beacon's identity (usually the ship's MMSI or a hex ID) and, in GNSS-equipped beacons, an encoded position of the order of a few hundred metres or better. A low-power 121.5 MHz homing signal allows aircraft and ships to direction-find in the final approach. Transmit duration is at least 48 hours. The beacon must be registered with the national authority, and the registration data (owner, ship, emergency contacts) must be current - an unregistered beacon delays rescue.
Mounting, battery and testing
Mount the beacon where it can float free if the ship sinks; the hydrostatic release unit and the battery have expiry dates that must be checked. Self-test according to the manufacturer's instructions, ideally in the first five minutes of a UTC hour, and never in a way that radiates a live distress alert.
SART and AIS-SART
A 9 GHz radar SART responds to a searching radar with a line of dots on the radar display, giving range and bearing. Place it at least 1 m above sea level, and use it only when survival craft are in the water: continuous operation flattens the battery. Typical performance is 96 hours standby and 8 hours transmitting, with a detection range of roughly 5 nm, more from a high antenna. An AIS-SART transmits AIS messages with the MMSI prefix 970 and appears on nearby AIS displays; it does not depend on the rescuer having a 9 GHz radar.
Worked example
A liferaft carries one radar SART and one AIS-SART. The radar SART paints on the searching vessel's X-band radar; the AIS-SART paints as a target on the AIS display. Together they cover both radar-equipped and AIS-equipped rescuers.
Traps
- Testing a SART in port, where it blocks radars for miles.
- Letting the HRU or battery expire unnoticed.
- Believing an EPIRB alert alone gives a precise position without registration and a GPS feed.