Chapter 10
EPIRBs and SARTs
Two ITEMS OF GMDSS EQUIPMENT that are only used in an extreme
emergency are:
EPIRB - Emergency Position Indicating Radio Beacon.
SART - Search And Rescue (radar) Transponder.
The function of the EPIRB is to give an indication of the position
of the distressed vessel, or survivors in the water/liferaft, through a satellite
system. The function of the SART is to help locate the distressed vessel,
or survivors in the water/liferaft, using radar transmission.EPIRBs
There are two types of satellite EPIRB in the GMDSS. The first
works through the Cospas-Sarsat satellite system. The second works
thought the Inmarsat satellite system. Both types can include a homing
beacon on 121·5MHz. There is provision in GMDSS regulations for an
EPIRB operating on VHF Ch70 and using DSC for the beacon signal.
This EPIRB is intended to be combined with a SART in a single unit. At
the time of writing, no manufacturer has produced such a device.
The Cospas-Sarsat network
The Cospas-Sarsat network (figure 10.1) utilises satellites in polar
orbit (the Low Earth Orbit Search and Rescue - LEO-SAR satellites)
and also in geo-stationary orbit (above the equator - the G EO-SAR
satellites). Both types of satellite will pick-up a distress alert from an
EPIRB transmitting on 406MHz and will relay that alert, through the
ground station (LUT), to the MRCC.
Older types of EPIRB have to have their position calculated by
Doppler effect - measuring the frequency change of the 406MHz
transmission caused by the movement of the polar-orbiting satellites. It
can take up to two hours for the LEOSAR satellites to calculate your
position and pass the information to the MRCC. More recently, with
the introduction of the GEOSAR satellites and new EPIRBs that
incorporate a G PS-calculated position into the transmission, your position
can be forwarded much more qUickly to the MRCC.
The GPS position can be passed through the GEOSAR satellites- if you are in sight of one of those satellites - and be at the MRCC
within a few minutes. The LEOSAR satellites will also pass that GPS
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