An Introduction to Global Maritime Distress Safety System (GMDSS)


During the 18th century, the ships sailing in international and coastal waters were dependent on the Morse code to send any kind of distress signal to coastal authority or ships in the nearby vicinity during emergency. Since it was a transmission of texture information using tones or lights, this kind of message was never clear to understand what kind of emergency is there on board ships. Therefore an internationally agreed safety procedure was adopted by IMO under SOLAS chapter IV which is known as GMDSS- Global Maritime Distress Safety System.



GMDSS and its Uses

On 1st Feb 1999, the fully implemented GMDSS came to picture. It is a set standard for usage of communication protocol, procedures and safety equipments to be used at the time of distress situation by the ship. Under GMDSS, all the passenger ships and cargo ship above 300 GT involved in the voyages in international waters have to carry equipments as per GMDSS.

When the ship uses GMDSS it basically sends a distress signal via a satellite or radio communication equipments. It’s also used as a medium for sending or receiving maritime safety information and general communication channel.

The different elements of GMDSS are as follows:

1.  INMARSAT:  It is a Satellite operated system which includes ship earth station terminals – Inmarsat B, C and F77. It provides telex, telephone and data transfer services between ship to ship, ship to shore, and shore to ship along with a priority telex and telephone service connected to shore rescue centres.

2.  NAVTEX: It is an internationally adopted automated system which is used to distribute MSI-maritime safety information, and includes weather forecasts and warnings, navigational warnings, search and rescue notices and other similar safety information.

3. High frequency: This element includes radio equipments of high frequency, which may be used as telephone and telex. The maritime safety information is sometime made on HF narrow band direct printing channels.

4. Emergency Position Indicating Radio Beacon (EPIRB): Read about EPIRB here.

5.  Search and Rescue Locating Equipment: Read about Search and Rescue equipment here.

6.  Digital Selective Calling (DSC): This is a calling service between ship to ship, ship to shore or vice versa for safety and distress information mainly on high or medium frequency and VHF maritime radio.

All the above mentioned elements have different working limitations depending upon the service providers and equipment capability. Therefore a division of areas has been done for the elements;

  • AREA 1 -   20 to 30 nm from shore for VHF coast station
  • AREA 2 – 100 to 150 miles from land (excluding Area 1) from shore based MF coast station.
  • AREA 3 – The area between roughly 76̊ north and 76̊ south, covered by geostationary maritime communication satellite.
  • AREA 4 – Remaining sea area including North Pole. Ship must carry HF, MF and VHF equipments while sailing in these areas.



Author: Anish Wankhede,