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Global Maritime Distress Safety System – GMDSS: During the 18th century, ships operating in international and coastal seas relied on the Morse code to communicate any distress signal to a coastal authority or adjacent vessels in the event of an emergency.

This type of notification was never very apparent to understand what kind of emergency onboard ships because it was a broadcast of textural information utilizing tones or lights.

As a result, the International Maritime Organization (IMO) adopted a globally approved safety protocol known as the GMDSS (Global Maritime Distress Safety System) under SOLAS Chapter IV.

Global Maritime Distress Safety System and Its Applications

The GMDSS was completely operational on February 1, 1999. It was a collection of guidelines for the ship’s communication protocol, procedures, and safety equipment to follow in a distressing emergency.

All passenger ships and freight ships over 300 GT that travel in international waters must carry GMDSS-compliant equipment.

When a ship employs GMDSS, it simply sends out a distress signal by satellite or radio. It delivers and receives navigational safety information and a general communication channel.

There are different sea areas to allot the working equipment in the respective area.

A120 to 50 MVHF DSC
A250 to 400 MVHF + MF
A370° N to 70° SVHF + MF + One INMARSAT
A4Above 70° N or SHF + MF + VHF

The following are the frequencies in a specific band:

  • Medium Frequencies: 300 kHz to 3 MHz
  • High Frequencies: 3 MHz to 30 MHz
  • Very High Frequencies: 30 MHz to 300 MHz

Very High Frequencies (VHF)

Distress, Urgency, and Safety communications are carried on Channel 16, set to 156.800 MHz. The VHF DSC (Digital Selective Calling) channel 70, set at 156.525 MHz, is for routine VHF DSC (Digital Selective Calling) monitoring.

To avoid interference on Channel 16, GUARD channels are placed above and below. Aside from distress, safety, and Urgency, it is impossible to have uninterrupted traffic on Channel 16 without interfering with other communications. 156.775 MHz and 156.825 MHz are the Guard channel frequencies.

The VHF set, for example, relies on a 24 Volt DC source and uses J3E type transmission for radiotelephony and G2B type transmission for data transmission.

The following are the many components of GMDSS:


It is a satellite-based system incorporating the Inmarsat B, C, and F77 ship earth station terminals. It provides ship-to-ship, ship-to-shore, shore-to-ship telex, telephone, and data transfer services.


It is an internationally recognized automated system for distributing MSI-maritime safety information, such as weather forecasts and alerts, navigational warnings, search and rescue notices, and similar safety information.

EPIRB (Emergency Position Indicating Radio Beacon):

An EPIRB is a piece of equipment that aids in determining the location of survivors during a search and rescue operation. It’s a backup method of distress signaling. Here’s where you can learn more about EPIRB.

Search and Rescue Locating Equipment (SART):

The Search and Rescue Radar Transponder is the most common piece of search and rescue equipment. This is used to direct Search and Rescue units to a distress location detected through questioning.

DSC (Digital Selective DSC (Digital Selective Calling)

It is a ship-to-ship, ship-to-shore, or call service that uses high or medium frequency and VHF maritime radio to communicate safety and distress information.

GMDSS Education

Handling GMDSS equipment necessitates certification and licensing from the department’s Telecommunications department. An officer must have a General Operators Certificate (GOC) before being allowed to use GMDSS equipment onboard the ship.

To earn this GOC, you must first complete a short course, after which you must pass a test (both written and oral) that must be given. This course is designed for Cadets who need to become licensed Radio Operators to operate all equipment by the GMDSS requirements.

The training lasts about 12 days, and because the course is required, it is recommended that you phone an accredited institute to reserve a spot for a future session.

The officer is taught many parts of GMDSS throughout the course, ranging from Radio Log to transmitting INMARSAT messages and all other components required when carrying out communication onboard. The written exam assesses theory, whereas the oral exam is a one-on-one session with a surveyor who assesses the candidate on all areas of GMDSS, encompassing the entire syllabus (theory and practical).

Admiralty List of Radio Signals (ALRS)

  • Distress Communication And False Alert
  • Operation Procedure For Use Of DSC Equipment
  • Search And Rescue Transponder
  • Extract From ITU Radio Regulations
  • VHF DSC List Of Coast Stations For Sea Area A1
  • MF DSC List Of Coast Stations For Sea Area A2
  • HF DSC List Of Coast Stations For Sea Area A3
  • Maritime Safety Information (MSI)
  • SafetyNet
  • Distress, Search And Rescue

Marine Radio (Portable)

The portable marine radio, also known as the survival craft transceiver, is a piece of equipment kept in the bridge if the ship’s crew has to board the survival craft. It can also be used for communication on board. It is utilized for on-scene coordination between the survival craft and the search and rescue personnel in an emergency. The following are the IMO criteria for survival craft transceivers:

  • Unskilled personnel can operate it.
  • 156.8 MHz (Channel 16) and 156.3 MHz (Channel 16) are used for transmission and reception (Channel 6)
  • Withstand a 1-meter drop
  • For 5 minutes, it was watertight to a depth of 1 meter.
  • A minimum power of 0.25 watts is required.
  • There is a power-saving switch accessible.
  • An omnidirectional, vertically polarised antenna is needed.
  • 8-hour battery power capacity (Nickel Cadmium or Lithium Battery)

The scope of GMDSS is broad, and the only way to improve at handling the equipment and learn more about the setup is to study extensively about it, whether through publications, manuals, or any other available means.

Because the GMDSS is a mandated setup onboard ships and a critical setup in emergencies, it is in the ship’s officer’s best interests to learn everything there is to know about it.

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