Survival Craft radio equipment
So, you have abandoned your sinking GMDSS vessel,
and you find yourself in a lifeboat or liferaft.
What now ?
Well the GMDSS doesn't stop yet - there are specific GMDSS radio systems developed for operation from survival craft.
These systems are designed to alert rescuers to your plight and guide them to your location.
Search And Rescue (Radar) Transponders (SARTs)
SART is a self contained, portable and buoyant Radar Transponder (receiver and transmitter).
SARTs operate in the 9 GHz marine radar band, and when interrogated by a searching ship's radar, respond with a signal which is displayed as a series of dots on a radar screen.
Although SARTs are primarily designed to be used in lifeboats or liferafts, they can be deployed on board a ship, or even in the water.
SARTs are powered by integral batteries which are designed to provide up to 96 hours of operation.
When activated, a SART responds to a searching radar interrogation by generating a swept frequency signal which is displayed on a radar screen as a line of 12 dots extending outward from the SARTs position along its line of bearing.
The spacing between each dot is 0.6 nautical miles.
As the searching vessel approaches the SART, the radar display will change to wide arcs. These may eventually change to complete circles as the SART becomes continually triggered by the searching ship's radar.
Although not an actual SART response, this
radar picture gives an impression of how a SART signal would be
Some slight position error will also be caused by the SART switching from receive to transmit mode.
SARTs will also provide a visual and audible indication to users when interrogated by a searching radar.
The range achievable from a SART is directly proportional to its height above the water.
A SART mounted at 1m (ie: in a liferaft) should be able to be detected at 5 nautical miles by a ship's radar mounted at 15m.
The same SART should be able to be detected at 30 nautical miles by an aircraft flying at 8000 feet.
GMDSS carriage requirements
GMDSS vessels from 300 to 500 GRT are required to carry 1 SART, and vessels over 500 GRT are required to carry 2.
Manufacturers have recently developed SARTs which work in conjunction with the VHF Automatic Identification System (AIS).
IMO has recognised AIS SARTs as being equivalent to radar SARTs for SOLAS carriage - i.e. ships can substitute an AIS SART for a radar SART.
The AIS SART comprises a two channel VHF AIS transmitter and a GPS receiver integrated into one waterproof enclosure - which is very similar in size to a traditional radar SART.
AIS SART technical paramaters are defined in IEC
Standard 61097-14. These can be summarised as follows:
Power output: 1 W EIRP
Transmitting frequencies: AIS channels 1 and 2
GPS receiver: 20 channel
Battery capacity: 96 hrs
Operating temperature: -20 to +55 C
The AIS SART transmits a sequence of 8 messages a minute. Each message is transmitted in a 26 millisecond time slot. 4 messages are transmitted on AIS channel 1 (161.975 MHz) and 4 on AIS channel 2 (162.025 MHz). This time frame is designed to maximise the period that the SART will be visable to other ships AIS receivers. Reception of only 1 of the 8 messages will enable accuratle location of the SART.
AIS SARTs are coded with a unique 9 digit identification code beginning with 970 - very similar to a DSC MMSI. The identification code is structured as follows:
970 is the SART prefix
XX is the manufacturer's 2 digit code
YYYY is the individual SART number
Shipboard AIS systems will recognise the 970 prefix as a SART, and display the target as a circle with a cross.
The AIS SART offers significent advantages over the radar version - the much lower operating frequency (160 MHz vs 9000 MHz) means that range is significantly increased. Moreover, because VHF can (to a certain extent) propagate around hills, SARTs can literally be seen 'around corners'.
More info on AIS SARTs can be found at the following manufacturer's websites:
Portable VHF transceivers
These units are designed to allow communications between searching vessels and survivors in liferafts. They operate on the VHF marine band in voice mode. DSC capability is not fitted.
The IMO performance standard requires that the equipment:
provide operation on VHF channel 16 (the radiotelephone distress and calling channel) and one other channel
be capable of operation by unskilled personnel
be capable of operation by personnel wearing gloves
be capable of single handed operation, except for channel changing
withstand drops on to a hard surface from a height of 1 metre
be watertight to a depth of 1 metre for at least 5 minutes, and maintain watertightness when subjected to a thermal shock of 45 degrees Celsius.
not be unduly effected by seawater or oil
have no sharp projections which could damage survival craft
be of small size and weight
be capable of operating in the ambient noise level likely to be encountered on board survival craft
have provisions for attachment to the clothing of the user
be either a highly visible yellow/orange colour or marked with a surrounding yellow/orange marking strip
be resistant to deterioration by prolonged exposure to sunlight
Typical GMDSS VHF portable transceivers
GMDSS carriage requirements
GMDSS vessels from 300 to 500 GRT are required to carry 2 VHF portables, and vessels over 500 GRT are required to carry 3.
Alas, the GMDSS is not perfect.....