What is Global Maritime Distress and Safety System or GMDSS and its details?

GMDSS Stands for Global Maritime Distress and Safety System This System was adopted by IMO in 1988 and replaced the 500 Khz MORSE CODE SYSTEM

Limitation of Morse Code System :-
  1. Short Range
  2. Manual Alerting
  3. Aural Watch keeping.
Points to pounder regarding GMDSS:

The Global Maritime Distress and Safety System  or GMDSS is an international system using advanced communications technology. Development of GMDSS was initiated by the International Maritime Organization (IMO) and the system represents a significant improvement in maritime communications.

GMDSS is designed to enhance ship-to-shore communications and provide rapid, automated distress alerting, with positional information if available. While compliance is mandatory for large cargo and passenger ships on international voyages or in the open sea, it is voluntary for recreational vessels. GMDSS will however have an impact on recreational boaters, and it is recommended that recreational boaters become familiar with its features. To help with the transition to GMDSS, Coast Guard stations will continue to monitor VHF channel 16 and MF frequency 2182 kHz for the foreseeable future. The mandatory equipped vessels however, discontinued monitoring MF frequency 2182kHz on February 1st, 1999, and are only obligated to monitor VHF channel 16 until February 1st, 2005. The GMDSS equipment on these vessels will instead be monitoring for digital data on VHF channel 70 and MF frequency 2187.5 kHz.


Which types of vessel GMDSS apply to:

  • GMDSS will apply to all Cargo Ship of 300 GT and above, and
  • To all passenger ship regardless of size on international voyage.

GMDSS is largely but not fully automated system. The GMDSS emphasizes the ability to alert SAR authorities ashore as well as shipping in the vicinity in order to receive a rapid co-ordinated response to distress situations.

Functional Requirements of GMDSS equipments :-

  1. Transmission of ship to shore distress alert by at least two separate and independent means, each using a different radio communication.
  2. Reception of shore – to ship distress alerts.
  3. Transmission and reception of Ship to ship distress alert.
  4. Transmission and reception of SAR (Search and rescue) coordinating communication.
  5. Transmission and reception of on-scene communication (At the point distress location)
  6. Transmission and reception of signals for locating.
  7. Transmission and reception of MSI (Maritime safety Information).
  8. Transmission and reception of general radio – communication to and from shore based radio system or networks; and
  9. Transmission and reception of bridge to bridge communications.


GMDSS divides the world’s oceans into four “sea areas”, designated A1 through A4.

About the author

Amit Sharma

Graduated from M.E.R.I. Mumbai (Mumbai University), After a brief sailing founded this website with the idea to bring the maritime education online which must be free and available for all at all times and to find basic solutions that are of extreme importance to a seafarer by our innovative ideas.

1 Comment

  • Man Overboard is a distress situation. Even the RT message will be Distress message . Information given that RT message will be Urgency is absolutely wrong. Students following this in GOC examination will fail. Request you to correct this. You may consult ITU manual for maritime mobile & maritime mobile satellite services.
    Thanking you

Leave a Comment

error: Content is protected !!