Yacht Insurance News What is GMDSS?
Global Maritime Distress and Safety System

Explanation by Inmarsat

The Global Maritime Distress and Safety System (GMDSS) is an international system that 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 cargo ships of 300 gross registered tonnes and upwards and all passenger ships 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 co-ordinated 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 ship’s staff do not have time to send out a full 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 Organisation (IMO), a specialised 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 fully take effect?
The final, global implementation of GMDSS became fully effective on 1 February 1999. On that date, all applicable ships had to comply with the GMDSS requirements in SOLAS.

Who has to comply with the GMDSS?
All ships subject to SOLAS Chapter IV have to fit GMDSS equipment. In general, this means, generally, all cargo ships over 300 gross registered tonnes and all passenger vessels 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 radio-communications 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 - all of which have different limitations with respect to coverage - 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 l50 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 76 North and 76 South.

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 also 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.


Distress Alerting:
The method of distress alerting can depend on the sea area in which the ship is saiing and alos on the equipment carried. The likely methods of initiating a distress alert in each of the four sea areas are shown below:

Sea Area A1
VHF DSC on Channel 70
VHF radiotelephony on Channel 16
MF DSC on 2187.5KHz

Sea Area A2
MF DSC 0n 2187.5KHz
VHF DSC on Channel 70
VHF radiotelephony on Channel 16

Sea Area A3
HF DSC on 8414.5KHz and all other HF DSC frequencies
F DSC on 2185.7KHz

Sea Area A4
HF DSC on 8414.5KHz and all other HF DSC frequencies
HF DSC on other frequencies to alert coast stations
MF DSC on 2187.5KHz
EPIRB (Cospas-Sarsat only)

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 or inadequately trained 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 at least 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 sometimes 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 will work?
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 co-operation with other Contracting Governments, appropriate shore-based facilities for space and terrestrial radio-communication services..."


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