SARTs
The initials SART stand for Search And Rescue Transponder, and refer to a device operating on radar frequencies, designed to produce a distinctive pattern on an approaching vessel’s radar.
A marine radar works by transmitting short pulses of super high frequency radio waves, which are focused into a tight beam by a directional antenna. When a pulse meets a “target”, such as a ship, it is reflected back to the radar. The time between transmission of the pulse and reception of the echo is directly related to the distance between the radar and the target. Of course, this only happens when the directional antenna is pointing at the target, so the direction the antenna is pointing corresponds to the direction of the target.
The range and bearing information is then used to “paint” a blob (called a “contact”) on the radar display, in a position corresponding to the target’s range and bearing.
A SART, however, does not merely reflect the radar pulse: it transmits a sequence of twelve pulses at very short intervals. On the radar screen, this appears as a string of twelve small contacts, starting at the position of the SART, and stretching outwards towards the edge of the screen, 0.6 miles apart.
As the vessel closes to within about a mile of the SART, the twelve contacts expand to wide arcs, and when the vessel reaches the SART, the arcs may expand even further, to form a pattern of twelve concentric circles.
The performance of a SART varies: although it should be visible to a ship’s radar at five miles or more, this reduces to less than two miles if the SART is lying on the floor of a liferaft, but can be as much as forty miles.
SARTs are primarily intended for use in liferafts, but can be used on any vessel.
A SART should generally be mounted as high as possible, and at least 1m above sea level.
Do not use a radar reflector and SART together.
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