NIMASA GMDSS GOC Exam key terms

The Global Maritime Distress and Safety System: an international framework of radio equipment, frequencies and procedures that lets ships alert rescue authorities and communicate with shore and other vessels, regardless of where the ship sails.

A sea area within continuous coverage of at least one VHF coast station equipped with DSC alerting, normally taken as roughly 20 to 30 nautical miles from the coast, where a ship can rely on VHF for distress communication.

A sea area outside A1 but within coverage of at least one MF coast station with DSC alerting, typically extending about 100 to 150 nautical miles offshore, where MF radio can be used for distress alerting and communication.

A sea area outside A1 and A2 covered by an Inmarsat geostationary satellite with continuous alerting capability, extending roughly between 70 degrees north and 70 degrees south, where satellite communication supports distress alerting.

The remaining sea areas outside A1, A2 and A3, essentially the polar regions beyond Inmarsat coverage, where distress alerting relies on HF DSC and other HF radiocommunication services.

The nine capabilities every GMDSS ship must provide, including distress alerting, receiving shore-to-ship distress alerts, transmitting and receiving SAR coordinating communications, on-scene communications, locating signals, MSI and general radiocommunications.

A priority transmission sent to alert rescue authorities that a vessel or person is in grave and imminent danger and needs immediate assistance, typically carrying the ship's identity and, where available, its position and the nature of the distress.

A distress alert or message transmitted on behalf of another vessel or person in distress, permitted only when the source cannot transmit itself, a station in distress cannot be contacted, or when a shore station or coordinator requests it.

The spoken radiotelephony distress signal, spoken three times, announcing that a station is in grave and imminent danger and requires immediate assistance, and given absolute priority over all other transmissions.

The radiotelephony urgency signal, spoken three times, used when a station has a very urgent message concerning the safety of a vessel or person but is not in immediate danger requiring distress assistance.

The radiotelephony safety signal, spoken three times, announcing an important navigational or meteorological warning, such as a gale warning, a drifting hazard or a navigational aid failure.

Digital Selective Calling: an automatic calling system used on VHF, MF and HF that sends a coded alert or call containing the called station's identity and the caller's identity, with a reason for the call and a suggested working channel.

Maritime Mobile Service Identity: a unique nine-digit number assigned to a ship station, used in DSC calls and other digital communications to identify the vessel or station being called or calling.

The automatic feeding of the vessel's position and time from a satellite navigation receiver into DSC, AIS and other GMDSS equipment, so that distress alerts and routine calls carry current location data.

A dedicated DSC receiver, separate from the main transceiver, that continuously monitors the distress and calling frequency for the sea area, allowing the radio officer to keep a listening watch while other work is done.

Designated minutes in each hour, such as the first three and last three minutes of the hour, when MF and HF radiotelephony calling is avoided so that distress traffic can be heard without interference.

Digital Selective Calling on the high frequency bands, using assigned frequencies within the 4, 6, 8, 12 and 16 MHz bands, to alert shore stations and ships over long distances when satellite coverage is unavailable.

A global satellite communications system providing voice, telex and data services to ships through geostationary satellites, used for distress alerting in Sea Area A3 and for routine and safety communications.

The Inmarsat Enhanced Group Call service that broadcasts Maritime Safety Information, such as navigational warnings and weather forecasts, to ships in a selected ocean region or area.

A narrow-band direct-printing service that broadcasts Maritime Safety Information on 518 kHz, and in some regions other frequencies, to ships within about 200 to 400 nautical miles of a coastal transmitter.

Maritime Safety Information: navigational and meteorological warnings, forecasts, search and rescue information and other urgent safety information broadcast to ships, received through NAVTEX, SafetyNET or other services.

The international NAVTEX frequency for English-language Maritime Safety Information broadcasts, received automatically by NAVTEX receivers and monitored continuously by ships fitted with the equipment.

The way radio waves travel from transmitter to receiver, including ground wave along the surface, sky wave refracted by the ionosphere, and line-of-sight space wave, each dominating at different frequencies and distances.

A radio wave that travels upward and is refracted back to earth by the ionosphere, allowing HF communication over long distances, with usable frequencies varying by time of day and solar activity.

A radio wave that follows the earth's surface, providing reliable communication at MF and lower frequencies over distances of a few hundred nautical miles, largely independent of time of day.

The international radiotelephony distress, safety and calling channel on 156.800 MHz, monitored by ships and coast stations for initial contact, with working channels used for the exchange that follows.

The dedicated VHF Digital Selective Calling channel on 156.525 MHz, reserved for DSC alerts and calls and not used for voice communication, monitored continuously by the DSC watchkeeping receiver.

Emergency Position Indicating Radio Beacon: a float-free transmitter, activated automatically or manually, that sends a distress alert with the vessel's identity and position via the COSPAS-SARSAT satellite system on 406 MHz.

The frequency used by COSPAS-SARSAT distress beacons, carrying digitally encoded identity and position information that allows rescue coordination centres to identify the vessel and locate the beacon quickly.

Search and Rescue Radar Transponder: a device carried on survival craft that, when triggered by an interrogating radar, responds with a signal producing a series of dots on the radar display to mark the craft's position.

A radar transponder that transmits an AIS position report identifying a survival craft, so that vessels with AIS can display the craft as a distress target on their navigation equipment.

A periodic check of a GMDSS battery, such as a capacity test or a specific gravity check, to confirm it can supply the required emergency load for the required period, as recorded in the maintenance log.

A dedicated battery or generator that can supply the GMDSS equipment for a specified period, such as one hour on a ship with a main source of power, or longer on ships without one.

The systematic process of tracing a radio equipment failure, using built-in tests, signal measurements and substitution of antennas or cables, to restore the equipment or report it as required.

The conductor or structure that radiates and receives radio waves, whose length, height, insulation and connection quality strongly affect the range and clarity of GMDSS communications.

The authorisation issued for a ship station and its radio operators, confirming that the equipment and personnel meet national and international requirements to use the maritime radio frequencies.

Unwanted radio energy that disrupts reception or transmission, caused by other transmitters, faulty equipment or electrical noise, and reported when it affects distress or safety communications.