GLOBAL
MARITIME DISTRESS AND SAFETY SYSTEM
The Global Maritime Distress and Safety System (GMDSS) represents
a significant improvement in marine safety over the previous
system of short range and high seas radio transmissions. Its
many parts include satellite as well as advanced terrestrial
communications systems. Operational service of the GMDSS began
on 1 February 1992, with full implementation scheduled by 1
February 1999.
The GMDSS was adopted by amendments in 1988 by the Conference
of Contracting Governments to the International Convention for
the Safety of Life at Sea (SOLAS), 1974. This was the culmination
of more than a decade of work by the International Maritime
Organization (IMO) in conjunction with the International Telecommunications
Union (ITU), International Hydrographic Organization (IHO),
World Meteorological Organization (WMO), International Maritime
Satellite Organization (INMARSAT), and others.
The GMDSS offers the greatest advancement in maritime safety
since the enactment of regulations following the Titanic disaster
in 1912. It is an automated ship-to-ship, shore-to-ship and
ship-to-shore system covering distress alerting and relay, the
provision of maritime safety information (MSI) and basic communication
links. Satellite and advanced terrestrial systems are incorporated
into a modern communications network to promote and improve
safety of life and property at sea throughout the world. The
equipment required on board ships will depend not on their tonnage,
but rather on the sea area in which the vessel operates. This
is fundamentally different from the previous system, which based
requirements on vessel size alone. The greatest benefit of the
GMDSS is that it vastly reduces the chances of ships sinking
without a trace and enables search and rescue (SAR) operations
to be launched without delay.
By the terms of the SOLAS Convention, the GMDSS provisions apply
to cargo ships of 300 gross tons and over and ships carrying
more than 12 passengers on international voyages. Unlike previous
shipboard carriage regulations that specified equipment according
to size of vessel, the GMDSS carriage requirements stipulate
equipment according to the area the vessel operates in. These
sea areas are designated as follows:
Sea Area A1 An area within the radiotelephone coverage of at
least one VHF coast station in which continuous Digital Selective
Calling (DSC - a radio receiver that performs distress alerting
and safety calling on HF, MF and VHF frequencies) is available.
This area extends from the coast to about 20 miles offshore.
Sea Area A2 An area, excluding sea area A1, within the radiotelephone
coverage of at least one MF coast station in which continuous
DSC alerting is available. The general area is from the A1 limit
out to about 100-300 miles offshore.
Sea Area A3 An area, excluding sea areas A1 and A2, within the
coverage of an INMARSAT geostationary satellite in which continuous
alerting is available. This area is from about 70°N to 70°S.
Sea Area A4 All areas outside of sea areas A1, A2 and A3. This
area includes the polar regions, where geostationary satellite
coverage is not available.
The International Maritime Satellite Organization (INMARSAT),
a key player within GMDSS, is an international consortium comprising
over 75 international partners who provide maritime safety communications
for ships at sea. In accordance with its convention, INMARSAT
provides the space segment necessary for improving distress
communications, efficiency and management of ships, as well
as maritime correspondence services. The basic components of
the INMARSAT system include the INMARSAT space segment, Land
Earth Stations (LES), also referred to as Coast Earth Stations
(CES), and mobile Ship Earth Stations (SES).
The INMARSAT space segment consists of 11 geostationary satellites.
Four operational INMARSAT satellites provide primary coverage,
four additional satellites serve as spares and three remaining
satellites serve as back-ups. The polar regions are not visible
to the operational satellites and coverage is available from
70°N to 70°S.
SafetyNET is a service of INMARSAT C’s Enhanced Group Call
(EGC) system. The EGC system is a method used to specifically
address particular regions or ships. Its unique addressing capabilities
allow messages to be sent to all vessels in both fixed geographical
areas or to predetermined groups of ships. SafetyNET is the
service designated by the IMO through which ships receive maritime
safety information.
SafetyNET is an international direct-printing satellite-based
service for the promulgation of navigational and meteorological
warnings, and distress alerts, forecasts, and other safety messages.
Messages can be transmitted either to geographic areas (area
calls) or to groups of ships (group calls).
NAVTEX is a maritime radio warning system consisting of a series
of coast stations transmitting radio teletype (standard narrow-band
direct printing, also sometimes called Sitor) safety messages
on the internationally standard medium frequency of 518 kHz.
It is a GMDSS requirement for the reception of MSI in coastal
and local waters. Coast stations transmit during previously
arranged time slots to minimize mutual interference. Routine
messages are normally broadcast four times daily. Urgent messages
are broadcast upon receipt, provided that an adjacent station
is not transmitting.
Maritime Safety Information (MSI)
Major categories of MSI for both NAVTEX and SafetyNET are:
1. Navigational warnings
2. Meteorological warnings
3. Ice reports
4. Search and rescue information
5. Meteorological forecasts
6. Pilot service messages (not in the U.S.)
7. Electronic navigation system messages (i.e., OMEGA, LORAN,
DECCA, GPS, DGPS, SATNAV, etc.)
Digital Selective Calling (DSC) is a method of automatically
placing a call directly from one radio to another. This is accomplished
by addressing the call so it will be received automatically
by the other radio. It permits a radio to be used like a telephone.
Since the DSC system will sound an alarm (much like a ringing
telephone) when it senses an incoming call, there is no need
for dedicated, aural watch-standing.
Emergency Position-Indicating Radio Beacons (EPIRBs) are designed
to transmit a satellite alert in the event of sudden accident
either automatically or manually. The automatic models are designed
and mounted so that they will float free of a sinking vessel
and be activated by seawater. The manual ones are controlled
by a switch.
