The Global Maritime Distress and Safety System - GMDSS

The Global Maritime Distress Safety System (GMDSS) is an internationally agreed-upon set of safety procedures, types of equipment, and communication protocols used to increase safety and make it easier to rescue distressed ships, boats and aircraft.

GMDSS consists of several systems, some of which are new, but many of which have been in operation for many years. The system is intended to perform the following functions: alerting (including position determination of the unit in distress), search and rescue coordination, locating (homing), maritime safety information broadcasts, general communications, and bridge-to-bridge communications. Specific radio carriage requirements depend upon the ship's area of operation, rather than its tonnage. The system also provides redundant means of distress alerting, and emergency sources of power

Components of GMDSS
The main types of equipment used in GMDSS are:

Emergency Position Indicating Radio Beacon - EPIRB

Cospas-Sarsat is an international satellite-based search and rescue system, established by Canada, France, the United States, and Russia. These four countries jointly helped develop a 406 MHz satellite Emergency Position-Indicating Radio Beacon (EPIRB), an element of the GMDSS designed to operate with Cospas-Sarsat system. These automatic-activating EPIRBs, now required on SOLAS ships, commercial fishing vessels, and all passenger ships, are designed to transmit to a rescue coordination center a vessel identification and an accurate location of the vessel from anywhere in the world. Newest designs incorporate GPS receivers to transmit highly accurate positions of distress. See: Search And Rescue Satellite Aided Tracking (SARSAT)

NAVTEX

Navtex is an international, automated system for instantly distributing maritime navigational warnings, weather forecasts and warnings, search and rescue notices and similar information to ships. A small, low-cost and self-contained "smart" printing radio receiver installed in the pilot house of a ship or boat checks each incoming message to see if it has been received during an earlier transmission, or if it is of a category of no interest to the ship's master.

INMARSAT

Satellite systems operated by the Inmarsat, under contract to the International Mobile Satellite Organization (IMSO), are also important elements of the GMDSS. Four types of Inmarsat ship earth station terminals are recognized by the GMDSS: the Inmarsat A, B, C and F77. The Inmarsat B and F77, an updated version of the A, provide ship/shore, ship/ship and shore/ship telephone, telex and high-speed data services, including a distress priority telephone and telex service to and from rescue coordination centers. The F77 is meant to be used with the Inmarsat C, since its data capability does not meet GMDSS requirements. The Inmarsat C provides ship/shore, shore/ship and ship/ship store-and-forward data and email messaging, the capability for sending preformatted distress messages to a rescue coordination center, and the Inmarsat C SafetyNET service. The Inmarsat C SafetyNET service is a satellite-based worldwide maritime safety information broadcast service of high seas weather warnings, NAVAREA navigational warnings, radionavigation warnings, ice reports and warnings generated by the USCG-conducted International Ice Patrol, and other similar information not provided by NAVTEX. SafetyNET works similarly to NAVTEX in areas outside NAVTEX coverage.

Inmarsat C equipment is relatively small and lightweight, and costs much less than an Inmarsat A, B or F77. Inmarsat A, B and F77 ship earth stations require relatively large gyro-stabilized antennas; the antenna size of the Inmarsat C is muchsmaller. Inmarsat also operates an EPIRB system, the Inmarsat L, which is similar to that operated by COSPAS-SARSAT. The INMARSAT L (also called INMARSAT E) EPIRB system is terminated by November 30th, 2006. The INMARSAT EPIRBs are replaced by COSPAS-SARSAT EPIRBs with built-in GPS. Immediate alerting is possible through the GEOSAR satellites of the COSPAS-SARSAT system.

In July 2002 IMSO notified IMO of the decision by Inmarsat to withdraw provision of Inmarsat A services as from 31 December 2007. On that date, Inmarsat A can no longer be used for any purpose. The last type approval by Inmarsat for a new model of maritime Inmarsat A mobile earth station was granted in 1991, since when no new Inmarsat A models have been approved.

Under a cooperative agreement with theNational Oceanic and Atmospheric Administration (NOAA), combined meteorological observations and AMVER reports can now be sent to both the USCG AMVER Center, and NOAA, using an Inmarsat C shipearth station, at no charge. SOLAS now requires that Inmarsat C equipment have an integral satellite navigation receiver, or be externally connected to a satellite navigation receiver. That connection will ensure accurate location information to be sent to a rescue coordinationcenter if a distress alert is ever transmitted.

High Frequency Radio - HF

The GMDSS includes High Frequency (HF) radiotelephone and radiotelex (narrow-band direct printing) equipment, with calls initiated by digital selective calling (DSC). Worldwide broadcasts of maritime safety information are also made on HF narrow-band direct printing channels.

Search and Rescue Radar Transponders - SART

The GMDSS installation on ships include one or more search and rescue radar transponder (SART) devices which are used to locate survival craft or distressed vessels by creating a series of dots on a rescuing ship's 3 cm radar display. The detection range between these devices and ships, dependent upon the height of the ship's radar mast and the height of the SART, is normally about 15 km (8 nautical miles). Note that a marine radar may not detect a SART even within this distance, if the radar settings are not optimized for SART detection.

 

Digital Selective Calling - DSC

The IMO also introduced Digital Selective Calling (DSC) on MF, HF and VHF maritime radios as part of the GMDSS system. 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 stations, groups of stations, or "all stations" in one's reach. Each DSC-equipped ship, shore station and group is assigned a unique 9-digit Maritime Mobile Service Identity.

DSC distress alerts, which consist of a preformatted distress message, are used initiate emergency communications with ships and rescue coordination centers. DSC was intended to eliminate the need for persons on a ship's bridge or on shore to continuously guard radio receivers on voice radio channels, including VHF channel 16 (156.8 MHz) and 2182 kHz now used for distress, safety and calling. A listening watch aboard GMDSS-equipped ships on 2182 kHz ended on February 1, 1999. In May 2002, IMO decided to postpone cessation of a VHF listening watch aboard ships. That watchkeeping requirement had been scheduled to end on 1 February 2005.

IMO and ITU both require that the DSC-equipped MF/HF and VHF radios be externally connected to a satellite navigation receiver. That connection will ensure accurate location information is sent to a rescue coordination center if a distress alert is ever transmitted. The FCC requires that all new VHF and MF/HF maritime radiotelephones type accepted after June 1999 have at least a basic DSC capability.

VHF digital selective calling also has other capabilities beyond those required for the GMDSS. The Coast Guard uses this system to track vessels in Prince William Sound, Alaska, Vessel Traffic Service. IMO and the USCG also plan to require ships carry a Universal Shipborne Automatic Identification System, which will be DSC-compatible. Countries having a GMDSS A1 Area should be able to identify and track AIS-equipped vessels in its waters without any additional radio equipment. A DSC-equipped radio cannot be interrogated and tracked unless that option was included by the manufacturer, and unless the user configures it to allow tracking.

GMDSS telecommunications equipment should not be reserved for emergency use only. The International Maritime Organization encourages mariners to use that equipment for routine as well as safety telecommunications.

GMDSS Sea Areas

GMDSS sea areas serve two purposes: to describe areas where GMDSS services are available, and to define what GMDSS ships must carry. Prior to the GMDSS, the number and type of radio safety equipment ships had to carry depended upon its tonnage. With GMDSS, the number and type of radio safety equipment ships have to carry depend upon the areas in which they travel. GMDSS sea areas are defined by governments.

In addition to equipment listed below, all GMDSS-regulated ships must carry a satellite EPIRB, a NAVTEX receiver (if they travel in any areas served by NAVTEX), an Inmarsat-C SafetyNET receiver (if they travel in any areas not served by NAVTEX), a DSC-equipped VHF radiotelephone, two or more VHF handhelds, and a search and rescue radar transponder (SART).

Sea Area A1
An area within the radiotelephone coverage of at least one VHF coast station in which continuous digital selective calling (ch70) alerting and radiotelephony services are available, as defined by the International Maritime Organization.

 

Sea Area A2
An area, excluding Sea Area A1, within the radiotelephone coverage of at least one MF coast station in which continuous DSC (2187.5 kHz) alerting and radiotelephony services are available, as defined by the International Maritime Organization. GMDSS-regulated ships travelling this area must carry a DSC-equipped MF radiotelephone in addition to equipment required for Sea Area A1.

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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. Ships travelling this area must carry either an Inmarsat A, B or C ship earth station, or a DSC-equipped HF radiotelephone/telex, in addition to equipment required for an A1 and A2 Area.

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Sea Area A4
The area outside that covered by areas A1, A2 and A3 is called Sea Area A4 Area. Ships travelling these polar regions must carry a DSC-equipped HF radiotelephone/telex, in addition to equipment required for areas A1 and A2.

 

MMSI

Under GMDSS every vessel has it’s own unique Maritime Mobile Service Identity (MMSI). An MMSI is composed of nine digits. A vessels MMSI is built into the DSC equipment and is not user-changeable. If a DSC unit is moved to another vessel, or the vessel is sold, a technician must re-program the MMSI.

MMSI’s can also be assigned to a group of vessels. This can prove invaluable, for example, to fishing fleets and shipping lines to keep in touch with other vessels within that group. A call made to a group rather than an individual MMSI will alert all vessels within that group.

The Maritime mobile Access & Retrieval System, maintained by the International Telecommunication Union is a searchable database which can be used to identify a vessel or coast stations MMSI number. The database is updated on a weekly basis.

MMSI Format

The first three non-zero digits of an MMSI number are used to distinguish the country of origin. Leading zero’s are used to distinguish between vessels (no leading zero’s), vessel groups (one leading zero), and coast stations (two leading zeros). For example:

232777777 - UK registered vessel
023266666 - Group of UK registered vessels
002325555 - Coast Radio Station