Search & Rescue Transponder (SART)

What sets a SART apart from an EPIRB

A SART does not alert anyone that a distress is happening; it only becomes useful once a search is already under way. It sits dormant until triggered, then responds to a searching vessel's or aircraft's radar with a distinctive series of arcs on the searcher's display, letting them home in on survivors' exact position, which an EPIRB's satellite position fix cannot do at the short range and poor visibility typical of an actual rescue.

Main components

Transponder unit

A compact, waterproof, floating unit, carried in the survival craft or a grab bag, designed to be operated by an untrained survivor under stress; increasingly available alongside an AIS-based alternative.

Radar transponder function

On activation, the X-band unit listens for a searching vessel's or aircraft's 9 GHz radar pulses and responds with a swept-frequency reply that appears as a line of dots or arcs on the searcher's radar display, extending outward from the survivors' position, visible at a useful range well before visual or voice contact is possible.

AIS-SART alternative

An AIS-SART transmits a distress position and identity directly on AIS frequencies, showing on any AIS-equipped vessel's chart display as a distinct distress symbol rather than a radar arc pattern; it is carried as an alternative to the radar SART where the vessel's equipment fit specifically allows the substitution.

Battery and mounting bracket

A sealed battery gives a minimum stated operating life once activated, commonly stated around 96 hours standby and 8 hours active transmission for radar SARTs; the unit is stowed in a bracket in the survival craft, with a lanyard so it can be mounted upright once deployed.

Regulations and class

SOLAS Ch. III/IV sets carriage requirements for SARTs by vessel category, typically requiring at least one unit per side or per rescue boat and liferaft complement, depending on ship type. GMDSS radio survey checks battery expiry and self-test function; a SART with an expired battery or failed self-test is a deficiency at annual survey even though it is only used in an actual emergency.

Typical faults

• Battery expired: unit may respond to self-test but cannot be relied on for full duration in a real search.
• Bracket corrosion or mounting damage: unit cannot be secured upright for effective radar response once deployed.
• Antenna damage from rough handling in the liferaft locker: reduced response range exactly when range matters most.
• Self-test not performed at the required interval: failure only discovered during an actual search.
• Confusion between radar SART and AIS-SART carriage requirements: vessel non-compliant if the wrong type is fitted for its SOLAS category.

What to look for in a supplier

• Correct type, radar SART or AIS-SART, matched to the vessel's SOLAS carriage requirement, confirmed against the ship's actual equipment list, not assumed.
• Stated battery standby and active transmission duration meeting or exceeding the regulatory minimum.
• Self-test function that does not require an actual radar or AIS transmission to verify, avoiding unnecessary alerts to nearby traffic.
• Robust bracket and lanyard arrangement suited to liferaft or rescue boat stowage conditions.

Practice mounting and activating the SART in a drill, not just checking the self-test light: in an actual search, an inverted or badly mounted unit gives a weak, intermittent return exactly when a strong one is needed.