Frequently Asked Questions about the GMDSS

GMDSS - Frequently Asked Questions

What is the GMDSS?
How does the GMDSS help in distress situations?
Who adopted the GMDSS?
Who is implementing the GMDSS?
When did the GMDSS take effect?
Who has to comply with the GMDSS?
What do ships have to do to comply with GMDSS?
What are the sea areas?

What about Morse code?
Do all ships have to have satellite communications?
What about the problem of false alerts?
What do coastal States have to do to ensure the GMDSS works?
What is the difference between GMDSS and previously existing radio communications?
What is DSC?
Can GMDSS equipment be used for routine radiocommunications?
What is COSPAS-SARSAT?
What is NAVTEX?
What is Inmarsat?
What are Search and Rescue Radar Transponders (SARTs)?
What about fishing vessels and small, recreational vessels such as yachts?
Can cellular telephones/mobile phones be used instead of VHF radio?
What is IMO doing to oversee GMDSS impementation?
Where can I find out more about the GMDSS?


What is the GMDSS?

The Global Maritime Distress and Safety System (GMDSS) is an international system which uses terrestrial and satellite technology and ship-board radio-systems to ensure rapid, automated, alerting of shore based communication and rescue authorities, in addition to ships in the immediate vicinity, in the event of a marine distress.

Under the GMDSS, all ocean-going passenger ships and cargo ships of 300 gross tonnage and upwards engaged on international voyages must be equipped with radio equipment that conforms to international standards as set out in the system. The basic concept is that search and rescue authorities ashore, as well as shipping in the immediate vicinity of the ship in distress, will be rapidly alerted through satellite and terrestrial communication techniques so that they can assist in a coordinated search and rescue operation with the minimum of delay.

How does the GMDSS help in distress situations?

Ships fitted with GMDSS equipment are safer at sea - and more likely to receive assistance in the event of a distress - because the GMDSS provides for automatic distress alerting and locating when a radio operator does not have time to send out a distress call. The GMDSS also requires ships to receive broadcasts of maritime safety information which could prevent a distress from happening, and requires ships to carry satellite emergency position indicating beacons (EPIRBs), which float free from a sinking ship and alert rescue authorities with the ship's identity and location.

Who adopted the GMDSS?

The GMDSS was adopted by the International Maritime Organization (IMO), a specialized agency of the United Nations with responsibility for ship safety and the prevention of marine pollution. The GMDSS was adopted by means of amendments to the International Convention for the Safety of Life at Sea (SOLAS), 1974. The amendments, contained in Chapter IV of SOLAS on Radiocommunications, were adopted in 1988 and entered into force on 1 February 1992 but provided for a phase-in period until 1 February 1999.

Who is implementing the GMDSS?

Implementation of the GMDSS requirements is the responsibility of Contracting Governments to SOLAS. This means the Administrations of individual countries that have ratified the GMDSS requirements into their national law. In practice, it also means that individual shipowners are responsible for ensuring their ships meet GMDSS requirements, since they must obtain certificates from their flag State certifying conformity with all relevant international regulations.

When did the GMDSS take effect?

The global implementation of GMDSS services became fully effective on 1 February 1999. By that date, all applicable ships had to comply with the GMDSS requirements in SOLAS.

GMDSS Countdown

Between 1 February 1992 and 1 February 1999 existing ships could comply with the Chapter IV of SOLAS in force prior to 1 February 1992 or the GMDSS.

All ships have been required to carry a NAVTEX (transmission of maritime safety information) receiver and satellite EPIRBs (emergency position-indicating radio beacons) since 1 August 1993

Ships built on or after 1 February 1995 must comply with all applicable GMDSS requirements

From 1 February 1999 all passenger ships and all cargo ships of 300 gross tonnage and upwards on international voyages must comply with the GMDSS

Who has to comply with the GMDSS?

All ships subject to SOLAS Chapter IV have to fit GMDSS equipment, generally, all passenger vessels and all cargo ships over 300 gross tonnage on international voyages.

What do ships have to do to comply with GMDSS?

Under SOLAS, every ship, while at sea, must have the facilities for essential communications, namely:

- transmitting ship-to-shore distress alerts by at least two separate and independent means;

- receiving shore-to-ship distress alerts;

- transmitting and receiving ship-to-ship distress alerts;

- transmitting and receiving search and rescue co-ordinating communications;

- transmitting and receiving on-scene communications

- transmitting and (as required) receiving signals for locating;

- transmitting and receiving maritime safety information;

- transmitting and receiving general radiocommunications to and from shore-based radio systems or networks; and

- transmitting and receiving bridge-to-bridge communications.

Specific equipment requirements for ships vary according to the sea area (or areas) in which the ship operates. The GMDSS combines various subsystems - which all have different limitations with respect tocoverage - into one overall system, and the oceans are divided into four sea areas:

- Area A1 Within range of VHF coast stations with continuous DSC alerting available (about 20-30 miles)

- Area A2 Beyond area Al, but within range of MF coastal stations with continuous DSC alerting available (about l00 miles)

- Area A3 Beyond the first two areas, but within coverage of geostationary maritime communication satellites (in practice this means Inmarsat). This covers the area between roughly 70 deg N and 70 deg S.

- Area A4 The remaining sea areas. The most important of these is the sea around the North Pole (the area around the South Pole is mostly land). Geostationary satellites, which are positioned above the equator, cannot reach this far.

Coastal vessels, for example, only have to carry minimal equipment if they do not operate beyond the range of shore-based VHF radio stations, but they may carry satellite equipment. However, some coasts do not have shore-based facilities, so although the ship is close to shore, the area counts as Area A2 or A3. Ships which do go beyond Sea Area A1 have to carry MF equipment as well as VHF - or Inmarsat satellite equipment. Ships which operate beyond MF range have to carry Inmarsat satellite equipment in addition to VHF and MF. Ships which operate in area A4 have to carry HF, MF and VHF equipment.

What about Morse code?

The invention of radio by Guglielmo Marconi and the use of Morse Code was a significant development in saving lives at sea after an incident. However, Morse telegraphy required many years of training and practice. If something happened to the radio operator, it was unlikely that anyone else on board would be able to use the telegraphy equipment. GMDSS equipment still requires training - but systems can automatically send a ship's position, speed and call sign when a distress button is pressed and advances in technology mean normal voice communication can be used, for example to speak to a rescue coordination centre.

Morse Code is therefore not a mandatory requirement under the GMDSS and many Governments are phasing out Morse Code listening services, if they have not already done so.

Do all ships have to have satellite communications?

No. If ships are travelling only in coastal areas served by VHF coast stations with continuous digital selective calling (DSC) available, they need only carry VHF equipment. However, they may use satellite communication in addition to, or instead of, terrestrial radio links.

What about the problem of false alerts?

One of the main reasons for false distress alerts is improper use of GMDSS equipment by untrained personnel. They are probably also caused by the lack of practical experience of GMDSS equipment onboard ships by trained personnel. IMO has issued guidelines on avoidance of false alerts and has introduced a standard button design, which means that the distress button has to be protected and must be held down for 3 seconds to be activated. There are problems with equipment design and poor training. EPIRBs have to be sensitive, because they have to be able to float free, and this sensitivity can lead to false alerts.

But information from manufacturers and coastal states indicate that, on average, there is only one false alert every 50 years from each of the alarms now available.

At the same time, the GMDSS system makes it possible for the ship in distress to be contacted, to check whether the alert is real or false, before search and rescue operations begin.

What do coastal States have to do to ensure the GMDSS works?

Under Regulation 5 of Chapter IV of SOLAS, "Each Contracting Government [to SOLAS] undertakes to make available, as it deems practical and necessary either individually or in cooperation with other Contracting Governments, appropriate shore-based facilities for space and terrestrial radiocommunication services..."

What is the difference between GMDSS and previously existing radio communications?

The GMDSS includes the regulations for radiocommunications aboard merchant ships contained in SOLAS Chapter IV. It includes some of the traditional maritime radio systems, but many have been upgraded to provide for automated listening and calling. The GMDSS utilises traditional radio communications, but integrates them into a coordinated system, adding satellite communications.

What is DSC?

Digital selective calling (DSC) has been introduced on VHF, MF and HF maritime radios as part of theGMDSS. 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 ships or groups of ships. DSC distress alerts, which consist of a preformatted distress message, are used to initiate emergency communications with ships and rescue coordination centres.

Fully implemented, DSC eliminates the need for persons on a ship's bridge or on shore to continuously guard radio receivers on voice radio channels used for distress, safety and calling, including VHF channel 16 (156.8 MHz) and 2182 kHz. A listening watch aboard GMDSS-equipped ships is scheduled to end on 2182 kHz on 1 February 1999, and on VHF channel 6 on 1 February 2005.

Can GMDSS equipment be used for routine radiocommunications?

Yes. GMDSS telecommunications equipment should not be reserved for emergency use only. IMO encourages mariners to use it for routine as well as safety radiocommunications.

What is COSPAS-SARSAT?

COSPAS-SARSAT is an international satellite-based search and rescue system, established by Canada, France, the U.S.A., and Russia. These four countries jointly helped develop a 406 MHz satellite emergency position-indicating radiobeacon (EPIRB), an element of the GMDSS designed to operate with COSPAS-SARSAT system. These automatic-activating EPIRBs are designed to transmit to a rescue coordination centre a vessel identification and an accurate location of the vessel from anywhere in the world.

What is 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. If it is a new and wanted message, it is printed on a roll of adding-machine size paper; if not, the message is ignored. A new ship coming into the area will receive many previously-broadcast messages for the first time; ships already in the area which had already received the message won't receive it again. No person needs to be present during a broadcast to receive vital information.

What is Inmarsat?

The International Mobile Satellite Organization (Inmarsat), previously the International Maritime Satellite Organization, was established by IMO in 1976 to operate satellite maritime communication systems and has become a privately owned company, while retaining its public sector obligations to the maritime distress and safety system.

Three types of Inmarsat ship earth station terminals are recognized by the GMDSS: the Inmarsat A, B and C. The Inmarsat A and B, 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 centres. The Inmarsat C provides ship/shore, shore/ship and ship/ship store-and-forward data and telex messaging, the capability for sending preformatted distress messages to a rescue coordination centre, and the SafetyNET service. The Inmarsat C SafetyNET service is a satellite-based worldwide maritime safety information broadcast service of high seas weather warnings, navigational warnings, radionavigation warnings, ice reports and warnings generated by the International Ice Patrol, and other similar information not provided by NAVTEX. SafetyNET works similarly to NAVTEX in areas outside NAVTEX coverage.

What are Search and Rescue Radar Transponders (SARTs)?

The GMDSS installation on ships include one or more search and rescue radar transponders, 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 less than about ten miles.

What about fishing vessels and small, recreational vessels such as yachts?

At the moment, most fishing vessels and recreational boaters are not required to participate in the GMDSS. But they will find many of the services available useful and may want to acquire equipment such as EPIRBs, which must be registered with the appropriate authorities.

Small vessels are also recommended to fit DSC equipment, since once the GMDSS is fully implemented, vessels without DSC will have difficulty contacting ships which are monitoring the DSC calling channel only. However, in a vessel traffic service zones, ships will still be required to maintain a listening watch on the appropriate frequency.

Most fishers and recreational boaters are already carrying VHF marine radios, however they are not generally DSC compatible.

Can cellular telephones/mobile phones be used instead of VHF radio?

Larger vessels must have the radio equipment specified in the GMDSS regulations. For smaller vessels, not covered by the GMDSS, most coastal authorities do not recommend cellular telephones as a substitute for the marine radio distress and safety systems in the VHF maritime radio band.

A VHF radio is more advantageous in that it can also help ensure that storm warning and other urgent marine information broadcasts are received. Furthermore, VHF radio can be used worldwide.

What is IMO doing to oversee GMDSS impementation?

IMO's Maritime Safety Committee (MSC) and Sub-Committee on Radio-Communications, Search and Rescue (COMSAR) are continually reviewing the GMDSS and its impelmentation. IMO also has a technical co-operation programme to help countries who need assistance, for example in setting up coastal faciltiies for the GMDSS.

Where can I find out more on the GMDSS?

Please see Information Resources on The Global Maritime Distress and Safety System - GMDSS

See also the IMO Directory of Maritime Links - choose the subject "Navigation and hydrography" for GMDSS links.