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The basic concept is that search and rescue authorities ashore as well as shipping in the immediate
vicinity of the ship in distress, will be rapidly alerted through satellite and terrestrial communication techniques so that
they can assist in a co-ordinated search and rescue operation with the minimum of delay.
How does the GMDSS help in distress situations?
Ships fitted with GMDSS equipment are safer at sea and more likely to receive assistance in the event
of a distress, because the GMDSS provides for automatic distress alerting the locating when a radio operator does not have
time to send out a distress call. The GMDSS also requires ships to receive broadcasts of maritime safety information which
could prevent a distress from happening, and requires ships to carry satellite emergency position indicating beacons (EPIRBs),
which float free from a sinking ship and alert rescue authorities with the ship's identity and location.
When did GMDSS take effect?
The global implementation of GMDSS services became fully effective on 1 February 1999. By that
date all applicable ships had to comply with GMDSS requirements in SOLAS.
Who has to comply with GMDSS?
All ships subject to SOLAS Chapter IV have to fit GMDSS equipment; generally, all passenger vessels
and all cargo ships over 300 gross tonnage on international voyages and most fishing vessels.
Specific equipment requirements for ships vary according to the sea area (or areas) in which the ship
operates. The GMDSS combines various subsystems which all have different limitations with respect to coverage, into one overall
system, and the oceans are divided into four sea areas:
Area A1. Within range of VHF coast stations with continuous DSC alerting available
(about 20 - 30 miles).
Area A2. Beyond area A1, but within range of MF coastal stations with continuous DSC
alerting available (about 100 miles).
Area A3. Beyond the first two areas, but within coverage of geostationary maritime
communication satellites (in practice this means Inmarsat). This covers the area between roughly 70 deg N and 70 deg S.
Area 4. The remaining sea areas. The most important of these is the sea around the
North Pole (the area around the South Pole is mostly land). Geostationary satellites, which are positioned above the equator,
cannot reach this far.
Coastal vessels, for example, only have to carry minimal equipment if they do not operate beyond the
range of shore-based VHF radio stations, but they may carry satellite equipment. However, some coasts do not have shore-based
facilities, so although the ship is close to shore, the area counts as Area A2 or A3. Ships which do go beyond Sea Area A1
have to carry MF equipment as well as VHF or Inmarsat satellite equipment. Ships which operate beyond MF range have to carry
Inmarsat satellite equipment in addition to VHF and MF. Ships which operate in area A4 have to carry HF, MF and VHF equipment.
What is DSC?
Digital selective calling (DSC) has been introduced on VHF, MF and HF maritime radios as part
of GMDSS. DSC is primarily intended to initiate ship/ship, ship/shore and shore/ship radiotelephone and MF/HF radiotelex calls.
DSC calls can also be made to individual ships or groups of ships. DSC distress alerts, which consist of a pre-formatted distress
message, are used to initiate emergency communications with ships and rescue co-ordination centres.
DSC eliminates the need for persons on a ship's bridge or on shore to continuously guard radio receivers
on voice radio channels used for distress, safety and calling. A listening watch aboard GMDSS equipped ships is scheduled
to end VHF channel 6 on 1 February 2005.
Can GMDSS equipment be used for routine radiocommunications?
Yes. GMDSS telecommunications equipment should not be reserved for emergency use only.
What about fishing vessels and small recreational vessels such as yachts?
At the moment some fishing vessels and recreational boaters are not required to participate in GMDSS.
But they may find many of the services available useful and may want to acquire equipment such as EPIRBs, which must be registered
on the EPIRB registry at Falmouth.
Small vessels are also recommended to fit DSC equipment, since without DSC vessels will havedifficulty
contacting ships which are monitoring the DSC calling channel only. However in vesseltraffic service zones, ships will still
be required to maintain a listening watch on the appropriate frequency.
Channel 16 listening watch
HM Coastguard Rescue Co-ordination centres continue to maintain listening watch
on channel 16, although this is often only a loudspeaker watch. This will continue for the present, but with the discontinuation
of the requirement for ships at sea to monitor channel 16, it will eventually be phased out altogether. Small boat owners
are encouraged to replace their existing VHF communications equipment with DSC, in order to guarantee that they will be able
to contact a shore station or another vessel in the event of an emergency.
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