The Global Maritime Distress and Safety System (GMDSS) provides distress alerting and search and rescue coordination for ships via satellite and terrestrial radio communications. It applies to commercial ships over 300 tons and passenger ships engaged in international voyages. By 1999, all covered ships were required to carry radio equipment determined by their area of operation, including VHF, MF, HF, and satellite phones. Coastal nations must also provide shore-based infrastructure like radio stations and rescue coordination centers to support GMDSS. NAVTEX broadcasts maritime safety information via radio telex to ships within 200 miles of coastal transmitters.

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Global Maritime Distress andGlobal Maritime Distress and
Safety SystemSafety System (GMDSS)(GMDSS)
A Brief By Lance Grindley

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General concept of GMDSSGeneral concept of GMDSS

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ApplicationApplication
 The GMDSS applies to vessels subject to the
SOLAS Convention - that is:
 Commercial vessels of 300 Gross Registered
Tons (GRT) and above and all passenger vessels,
engaged on international voyages.
 The GMDSS became mandatory for such vessels
as from February 1, 1999.
 Commercial vessels under 300 GRT, or those
above 300 GRT engaged on domestic voyages
only are subject to the requirements of their Flag
State. Some Flag States have incorporated
GMDSS requirements into their domestic marine
radio legislation - however many have not.

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GMDSS: Implementation CalendarGMDSS: Implementation Calendar
 1.7.1991: Entry into force of the Radio
Regulations (gradual implementation of
GMDSS)
 1.2.1992: Entry into force of the 1988
Amendments to SOLAS Convention (IMO)
specifying (for SOLAS ships):
– new ships built after 1.2.1992: SART and two-
way VHF RTF apparatus for survival craft;
– After 1.8.1993: all ships with NAVTEX
receiver and S-EPIRB;

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– After 1.8.1993: all ships with NAVTEX
receiver and S-EPIRB;
– After 1.2.1995: all ships will have to carry at
least one radar capable of operating in the 9
GHz band, and SART and two-way VHF RTF
apparatus for survival craft ;
– new ships built after 1.2.1995 must comply
with all applicable GMDSS requirements
– After 1.2.1999: all ships must comply with the
GMDSS

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Functional requirementsFunctional requirements
 The GMDSS regulations (chapter IV of the
International SOLAS Convention), require that
every GMDSS equipped ship shall be capable of;
 transmitting ship-to-shore Distress Alerts by at
least two separate and independent means, each
using a different radio communication service;
 receiving shore-to-ship Distress Alerts;
transmitting and receiving ship-to-ship Distress
Alerts;
 transmitting and receiving search and rescue co-
coordinating communications;
 transmitting and receiving on-scene
communications;

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transmitting and receiving locating and
homing signals;
receiving maritime safety information;
transmitting and receiving general
radiocommunications relating to the
management and operation of the vessel;
transmitting and receiving bridge-to-bridge
communications.

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Equipment vs. OperationalEquipment vs. Operational
requirementsrequirements
 The major difference between the GMDSS and
its predecessor systems is that the radio
communications equipment to be fitted to a
GMDSS ship is determined by the ship's area of
operation, rather than by its size.
 Because the various radio systems used in the
GMDSS have different limitations with regards
to range and services provided, the new system
divides the world's oceans into 4 areas:

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 Area A1 lies within range of shore-based VHF
coast stations (up to about 50 nautical miles);
 Area A2 lies within range of shore based MF
coast stations (excluding A1 areas) (up to about
150 nautical miles);
 Area A3 lies within the coverage area of
Inmarsat communications satellites (excluding
A1 and A2 areas - approximately between
latitude 70 degrees north to latitude 70 degrees
south); and
 Area A4 comprises the remaining sea areas
outside areas A1, A2 and A3 (the polar regions).

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GMDSSGMDSS communication systemscommunication systems
 The GMDSS utilizes both satellite and terrestrial
radio systems as appropriate:
 Sea Area A1 (short range) - VHF is used to
provide: 1) DSC alerting on CH-70, 2) Distress
and Safety voice communications on CH-16.
 Sea Area A2 (medium range) – MF Frequencies
are used to provide : 1) DSC alerting, 2)
Distress and safety communications on voice and
NBDP.
 Sea Areas A3 and A4 (long range) - HF &/or
SES are used to provide: 1) alerting, 2) Distress
and Safety communications both voice and
NBDP.

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GMDSS: Ship equipmentGMDSS: Ship equipment
carriage requirementscarriage requirements
A1
A2
A3
A4
VHF equipment
S-EPIRB or VHF EPIRB
MSI receiver
VHF and MF equipment
S-EPIRB
MSI receiver
VHF, MF and HF or satellite
equipment
S-EPIRB
MSI receiver
VHF, MF and HF equipment
406 MHz S-EPIRB
MSI receiver

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Shore infrastructureShore infrastructure
 Each signatory country to the SOLAS
Convention (basically, all of the world's major
shipping nations) is obliged to enforce the
appropriate carriage of GMDSS radio equipment
and service documents by vessels sailing under
their national flag; and also to provide suitable
GMDSS shore-based infrastructure, including
Coast radio stations, RCC and Search and Rescue
units.
 However, the shore based infrastructure may be
provided in conjunction with neighboring states,
as appropriate.

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Maritime Mobile Service Identities (MMSI)Maritime Mobile Service Identities (MMSI)
All DSC equipment is programmed with a
unique nine digit identification number,
known as a
Maritime Mobile Service Identity (MMSI).
The MMSI is sent automatically with each
and every DSC transmission made.

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Maritime Identification Digits (MID)Maritime Identification Digits (MID)
Maritime Identification Digits (MID)
The first three digits of the MMSI are
known as the
Maritime Identification Digits (MID). The
MID represents the country of registration
(FLAG) of the vessel. MID's are allocated
on an international basis by the ITU, in
much the same way as the international
series of call-sign prefixes are.

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N A V T E XN A V T E X
Introduction
The NAVTEX system is used for the
automatic broadcast of localized Maritime
Safety Information (MSI) using Radio
Telex, NBDP.
The system operates on the Medium wave
Frequency band. The system range is
generally about 200 or so nautical miles
from the transmitter.

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Major service areas of NAVTEX coverage
include the Mediterranean Sea, the North
Sea, coastal areas around Japan and areas
around the North American continent.
The NAVTEX system is designed to be
used in GMDSS Sea Area A2, and is
utilized mainly by those countries with
relatively small areas of coastline and/or
sea areas to cover.

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Frequency of operationFrequency of operation
The NAVTEX system has been allocated
three broadcast frequencies:
518 kHz - the main NAVTEX channel
490 kHz - used for broadcasts in local
languages (i.e.: non-English)
4209.5 kHz - allocated for NAVTEX
broadcasts in tropical areas - not used at
the moment.

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 In real terms, 518 kHz is the only NAVTEX
channel used - this means that all broadcasts
from stations within the same NAVAREA must
be coordinated (IMO) on a time sharing basis to
eliminate interference.
 In addition, power outputs from each station are
adjusted to control the range of each broadcast.
This is particularly important during night-time
hours, as Medium Frequencies tend to travel
further after dark.

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CONCLUSIONSCONCLUSIONS
 Unprecedented international cooperation over a
period of about 10 years, involving IMO, ITU,
IHO, WMO, INMARSAT and the COSPAS-
SARSAT partners, has resulted in the maritime
community being provided with an integrated
distress and safety system
 The provision of appropriate international
regulations concerning the operation and
implementation of the system has been
successfully completed

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 The implementation of the system and its
efficient operation would considerably depend
upon the establishment of shore based facilities
by the Members and proper network
arrangements that will include:
– maritime satellite and terrestrial radio
services between the coast and ships,
– connections between coast stations and CES
and RCCs,
– telecommunication interconnections between
RCCs.