The Global Maritime Distress and Safety System (GMDSS) is a worldwide communication service that utilizes automated systems—both satellite and terrestrial—to provide distress alerts and disseminate maritime safety information for sailors. The system categorizes the oceans into four sea areas, which determine the equipment requirements for GMDSS based on the operational sea area of a vessel.
Sea Area A1 is within the range of VHF coastal radio (approximately 25 nautical miles).
Sea Area A2 falls within the range of coastal MF radio (about 100 nautical miles).
Sea Area A3 includes areas served by INMARSAT, covering the globe up to about 70°N and S, excluding polar regions.
Sea Area A4 encompasses the remaining navigable waters in polar regions.
One key function of this system is the broadcasting of Maritime Safety Information (MSI), which includes navigational and meteorological warnings, forecasts, and other urgent safety-related messages sent to vessels via SafetyNET and NAVTEX.
SafetyNET is a component of the Inmarsat C Enhanced Group Call system's safety service. It provides an automated and straightforward method for ships to receive MSI, with the message-selection capabilities of SafetyNET receivers allowing for customization of safety information to meet mariners' needs. The coordination of meteorological warnings and forecasts is managed through twenty-one METAREAs, each designated as a specific geographical sea area for which a particular country is responsible for issuing final bulletins in English.
For METAREA I, the responsibility falls to the United Kingdom, which issues storm warnings and provides High Seas Bulletins broadcast twice daily at 0930 and 2130 UTC. The High Seas Bulletin comprises three sections: Storm Warnings, General Synopsis, and Forecasts for the respective sea areas.
NAVTEXNAVTEX is the terrestrial communication component of the GMDSS. It is an automated direct-printing service that operates globally on a frequency of 518 kHz, with transmissions designed to reach a maximum range of 400 nautical miles. A NAVTEX receiver can be configured to receive messages from specific transmitting stations and particular classes of messages. However, certain critical message types cannot be filtered out. These include distress messages, search and rescue communications, navigational warnings, and meteorological alerts.
The character in position 3 is a letter (A-Z) that identifies the NAVTEX coastal radio station.
The format of the NAVTEX message follows a structured template
The format of the NAVTEX message follows a structured template commonly used in maritime warnings. Here’s a breakdown of the message components:
ZCZC FA57: This indicates the start of the message, with "ZCZC" signaling a new message and "FA57" representing the specific warning series or type.
271000 UTC OCT: This shows the date and time when the warning was issued, formatted in UTC (Coordinated Universal Time) as "day hour minute month."
WZ NORTH ATLANTIC: This denotes the geographical area affected by the warning.
NAV WARNING NR 195/24: This states the warning number, allowing mariners to easily reference specific warnings.
Warning Details: The main body of the message describes the nature of the warning, including conditions (e.g., gale warning) and expected impacts (e.g., rough seas, poor visibility).
Position and Time: Indicates the specific geographical position and the time related to the conditions mentioned.
NNNN: This signals the end of the message.
All messages broadcasts on 518kllz are in English and in the following format, ZCZC indicates the start of the message:
ZCZC
B1,B2,B3,B4
MESSAGE TEXT
NNNN
The success of NAVTEX has prompted various countries to adopt the frequencies of 490 kHz or 4209.5 kHz for disseminating additional information, such as forecasts for inshore waters and Maritime Safety Information (MSI) in their national languages. This information is particularly valuable for small craft. However, it is important to note that the output on the 518 kHz frequency serves as the primary source of essential MSI for all classes of vessels.
Broadcasts made on 518 kHz are part of the International NAVTEX service, whereas transmissions on alternative frequencies are categorized as National NAVTEX services and do not fall under the jurisdiction of the Global Maritime Distress and Safety System (GMDSS).
For comprehensive details regarding MSI broadcasts by the United Kingdom, refer to the relevant section, which includes information compliant with GMDSS regulations, as well as additional services.
Additional information regarding the GMDSS can be found in the following publications:
GMDSS Manual — IMO Publishing
International SafetyNET Manual — IMO Publishing
NAVTEX Manual — IMO Publishing
Admiralty List of Radio Signals, Vol. 5 — UK Hydrographic Office
Admiralty List of Radio Signals, Vol. 3(1) and Vol. 3(2) — UK
Evolution of Weather Information in Shipping History - Marine Public
Web access is available for forecasts and warnings concerning the High Seas globally, including the Shipping Forecast, the High Seas forecast for METAREA 1, and NAVTEX meteorological warnings issued by the United Kingdom Met Office. Access this information via the WMO Joint Commission for Oceanography and Meteorology (JCOMM) website.
Volume 5 of the Admiralty List of Radio Signals includes a list of websites that provide weather and ice information; however, it should be noted that these resources are not part of the official MSI system. Further details regarding radio facsimile stations, transmission schedules, and the types of weather and ice charts relevant to shipping can be found in Volumes 3(1) and 3(2) of the Admiralty List of Radio Signals.
Broadcasts are accessible in the eastern and northeastern regions of the North Atlantic from Northwood in the United Kingdom and Hamburg/Pinneberg in Germany. With proper communication, ships can also access a variety of charts from the websites of meteorological services.
