Search and Rescue Radar Transponders (SARTS)
SARTS, (Search and Rescue Radar Transponders), are location beacons that send a homing signal when interrogated by a 9 GHz radar.
SART's are normally carried on the ship's bridge or similar convenient place where they are readily accessible.
SART's are checked on a monthly basis to ensure correct operation by activating the test facility (the test is a low power transmission).
A SART can be checked by briefly activating it using the test facility and subjecting it to one or two passes of the ship's radar, however it is important that the local vessels are informed before this takes place.
When deploying a SART, read the manufacturer's instructions carefully. Once the SART has been switched on it should be attached to the highest point available, normally this will be achieved by fixing it to a supplied, one metre long telescopic pole and positioning this through the life raft's antenna opening. If a radar reflector is in place on the life raft, it must be removed when the SART is deployed as it can reflect radar signals from a search vessel before they cause the SART to react. When abandoning a vessel fitted with its own radar, the radar must be switched off before deploying the SART or the SART will be prematurely activated.
Once a SART has been activated, it will react to a 9 GHz radar signal, sending back its own transmission. This transmission will be displayed on the radar screen of the rescue vessel as a line of up to twelve 'blips' along the bearing of the SART, with the first echo as the target. The detection range of a SART varies depending upon the height of the radar and the height of the SART. A Lifeboat searching for a life raft can expect to make contact at about five to six miles. An aircraft at 3,000 feet could detect the same SART from about 48 miles.
SART's are triggered by 9GHz radars from different sources.
Initial detection of a SART indicating range and bearing
As the SART gets closer the dots turn to arcs
Within 1 mile of the SART the screen is cluttered
As the range decreases the 'blips' will grow, becoming arcs. At about one mile range, these arcs will become a series of concentric circles. It has been found that the best results for locating a SART can be obtained by setting the search radar to a 12 miles range, before switching to six miles as the range decreases.
Obtaining an accurate bearing to the casualty becomes increasingly harder as the range decreases and the 'blips' become arcs, and impossible when the arcs become concentric circles. In poor visibility it may be necessary to make several passes from different directions and triangulate the bearings before the position of the SART can be accurately determined.
Once contact has been made with the Liferaft and the SART turned off, erect the radar reflector to aid location. The radar reflector MUST NOT be used at the same time as the SART.
A second type of SART is on the market and this is aimed at the A.I.S. system. The Automated Identification System transmits data on the VHF channels 87 and 88. The A.I.S. SART incorporates an onboard GPS which will transmit positional data every minute. Only vessels and shore stations fitted with an A.I.S. receiver will be able to detect the A.I.S. SART. Space based A.I.S. is in its early stages of developement and may also be able to detect the transmissions.
As well as updatable positional information the A.I.S. SART has a unique MMSI number that starts with 970 followed by 6 numbers making a 9 digit MMSI number ie 970991234. The A.I.S. SART will be carried and used in a liferaft to indicate a survivors position in the water.
