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The Global Maritime Distress and Safety System (GMDSS) is an international system with world-wide availability to ensure rapid, automated alerting of shore-based stations and rescue authorities, in addition to ships in the immediate vicinity, so that they can assist in a coordinated search and rescue operation with the minimum of delay in the event of a marine distress. Another important feature of GMDSS is the reliable dissemination of maritime safety information. Technically, the GMDSS system is built up with different complementary communication components, including advanced terrestrial radio stations and satellite systems.

GMDSS was introduced by the International Maritime Organization in 1992 and obtained full operability in 1999. It replaces the previous ship-to-ship safety system, which relied on a manual Morse Code system and voice radio telephony on VHF Channel 16 and MF 2182 kHz. Today, the GMDSS system offers an automated ship-to-ship, ship-to-shore and shore-to-ship distress alerting and relaying system using satellites and terrestrial radio stations with Digital Selective Calling (DSC) technology.

The GMDSS is mandated for international commercial shipping by the IMO Safety of Life at Sea (SOLAS) Convention 1974, as amended in 1988. More specific, the IMO has mandated that from 1 February 1999 all passenger ships and all cargo ships of 300 gross tonnages and upwards on international voyages must comply with the GMDSS. Commercial vessels under 300 GRT, such as pleasure yachts, or those above 300 GRT engaged on domestic voyages only are subject to the requirements of their Flag State.

Vessels to which the GMDSS requirements apply are classified as SOLAS vessels while those to which GMDSS requirements do not apply are considered as non-SOLAS vessels.

GMDSS Equipment

GMDSS primary deals with communication and data transmission equipment, which must enable fast, accurate and reliable distress alerting. Different communication technologies are available for this purpose and the choice of equipment depends on the distance that has to be bridged to the closest land-based Rescue-Coordination Center (RCC).

GMDSS dictates that the communication equipment fitted on board ships depend on the area of operation of the ship rather than the size. Because the various communication systems used in the GMDSS have different limitations with regard to range and services provided, GMDSS divides the world's oceans into 4 Sea Areas:

  • Sea Area 1: is an area within coverage of at least one VHF coast station in which continuous DSC alerting is available, nominally in the range of 20 - 30 nautical miles
  • Sea Area 2: is an area, excluding Sea Area 1, within the coverage of at least on MF coast station in which continuous DSC alerting is available, nominally in the range of 100 - 150 nautical miles
  • Sea Area 3: is an area, excluding A1 and A2, within the coverage of an INMARSAT geo-stationary satellite coast station in which continuous alerting is available - approximately between 70 degrees north latitude and 70 degrees south latitude
  • Sea Area 4: is the remaining area outside A1, A2 and A3 (the polar regions)
Depending on the area being cruised, the following GMDSS equipment may be required (summary):
  • VHF radio with Digital Selective Call (DSC),
  • VHF hand-held radio,
  • MF/HF SSB communication equipment with DSC capability,
  • Satellite communication equipment for INMARSAT-B or -C,
  • EPIRB (Emergency Position Indicating Radio Beacon) to participate in the COSPAS-SARSAT Search and Rescue (SAR) system,
  • Search-and-Rescue Radar transponder (SART),
  • NAVTEX receiver for weather information and navigational warnings by telex over radio.

Smaller ships and pleasure yachts are non-SOLAS vessels and are not required to have any GMDSS equipment installed. However, they may be equipped accordingly by choice and can then participate in the GMDSS giving access to the global Search-and-Rescue facilities.

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