Introduction to GMDSS
The old maritime distress and safety system as defined in the 1974 SOLAS Convention was based on the requirement that certain classes of ships (classed by tonnage), when at sea, keep continuous radio watch on the international distress frequencies assigned in accordance with the ITU Radio Regulations and carry radioequipment capable of transmitting over a minimum specified range. The system includes two major manually operated sub-systems:
- the Morse telegraphy system on 500 kHz (MF);
- the radiotelephony system on 2182 kHz (MF) and 156.8 MHz (channel 16 VHF).
The main disadvantages of this system are as follows:
- a highly trained Morse code operator is needed;
- a continuousradio listening watch on specific distress frequencies;
- a limited range of communications (100-150 nautical miles).
The rapid development of digital technology and satellite communications has made it possible to significantly improve the safety of life at sea.
The International Maritime Organization (IMO) Assembly, at its eleventh session in 1979, considered the existingarrangements for maritime distress and safety communications. It was decided that a new global maritime distress and safety system should be established to improve distress and safety radio communications and procedures.
In 1988, the Conference of Contracting Governments to the 1974 SOLAS Convention on the Global Maritime Distress and Safety System (GMDSS) adopted amendments to the 1974 SOLAS Conventionconcerning radio communications for the GMDSS. These amendments entered into force on 1 February 1992. The GMDSS has been fully implemented on 1 February 1999.
Basic concept of the GMDSS
The old system is primarily intended for ship-to-ship operation in case of distress.
The basic concept of the GMDSS is that search and rescue authorities ashore, as well as shipping in the immediatevicinity of the ship in distress, will be rapidly alerted to a distress incident so they can assist in a coordinated search and rescue operation with the minimum delay. The system also provides for urgency and safety communications and the promulgation of maritime safety information.
The GMDSS lays down nine principal communications functions which all ships, while at sea,need to be able to perform:
1) transmitting ship-to-shore distress alerts by at least two separate and independent means, each using a different radio-communication service;
2) receiving shore-to-ship distress alerts;
3) transmitting and receiving ship-to-ship distress alerts;
4) transmitting and receiving search and rescue coordinating communications;
5)transmitting and receiving on-scene communications;
6) transmitting and receiving signals for locating;
7) transmitting and receiving maritime safety information;
8) transmitting and receiving general radio communications from shore-based radio systems or networks;
9) transmitting and receiving bridge-to-bridge communications.
Radio communication services
Thefollowing radio services are provided for the GMDSS:
• a radio communication service utilizing geostationary satellites in the maritime mobile satellite service (INMARSAT);
• a radio communication service utilizing polar orbiting satellites in the mobile satellite service (COSPAS-SARSAT);
• the maritime mobile service in the bands between 156 MHz and 174 MHz;
• the maritimemobile service in the bands between 4,000 kHz and 27,500 kHz;
• the maritime mobile service in the bands 415 kHz to 535 kHz and 1,605 kHz and 4,000 kHz.
GMDSS Sea areas
Radio communication services incorporated in the GMDSS system have individual limitations with respect to the geographical coverage and services provided. The range of communication equipment carried on board the ship is...