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This lesson explains the purpose, components, and requirements of a vessel’s Global Maritime Distress and Safety System (GMDSS). The lesson includes Port State Control examination points as well as indicators that an expanded inspection may be warranted.

• STATE the purpose of GMDSS.
• IDENTIFY the components of GMDSS
• BE FAMILIAR with the requirements of vessels operating in each sea area, and the proper functioning of GMDSS equipment.
• DEMONSTRATE an understanding of GMDSS equipment and certification issues that would indicate non-compliance with international conventions.

• SOLAS 74, Chapter IV
• STCW 95, Chapter IV


GMDSS: is the acronym for the Global Maritime Distress and Safety System.

GMDSS is an integrated communication system that uses satellite and terrestrial radio communications equipment to establish communication between land units and vessels at sea (ship-to-shore, shore-to-ship, and ship-to-ship).

2. DSC: is the acronym for Digital Selecting Calling.  DSC is the signaling method that, through a control unit, monitors the required frequencies and lets the radio operator know if there is a call for his or her station, and whether that call is distress, urgent, or routine. DSC is the fundamental reason why GMDSS is different from previous communications systems.

3. MF/ HF: represents Medium Frequency/High-Frequency designation communications.

4. MSI: is the acronym for Maritime Safety Information, which of navigational and meteorological warnings, meteorological forecasts, and other urgent safety-related messages broadcast to ships. It is a functional requirement of GMDSS for all ships to be able to receive MSI. MSI may be received by three systems: NAVTEX, safety NET, and HF NBDP.

5. NBDP: is the acronym for Narrow Band Direct Printing, which is the text messaging system for receiving MSI over HF

6. SafetyNET: is the INMARSAT system for receiving

7. EPIRB: is the acronym for Emergency Position Indicating Radio B It is a device that broadcasts a signal that is intercepted by a satellite and translated into a position on earth so that rescue units may be dispatched to the scene.

8. SART: is the acronym for Search and Rescue Transponder. SARTs automatically transmit a signal upon reception of a designated incoming signal from a 3-cm. radar unit. The signal transmitted by the SART appears as a distinctive pattern on a nearby vessel’s radar to alert that vessel to the presence of an active SART (probably a vessel in distress), and its location relative to the vessel.

9. STC: is the acronym for a Survival Craft Transceiver. These are portable two-way VHF transceivers that can be used for on-scene communications and onboard

10. INMARSAT: is the acronym for International Maritime Satellite Organization. It is a treaty organization that pioneered the emergency and routine use of satellite communications at sea. This acronym is used mostly to indicate the pieces of equipment that have access to the communication satellites, namely, INMARSAT B, C, and Fleet

11. Sea Areas: of the oceans into four different areas for the purposes of identifying GMDSS system components required by a vessel to comply with GMDSS regulations.

12. MMSI: this stands for Maritime Mobile Service Identity. Maritime Mobile Service Identities are formed of a series of nine digits that are transmitted over the radio path in order to uniquely identify ship stations, ship earth stations, coast earth stations, and group calls. These identities are formed in such a way that the identity or part thereof can be used by telephone and telex subscribers connected to the general telecommunications network principally to call ships automatically.


  1. BACKGROUND: Prior to  GMDSS,  most radio communication from ships was initiated by making a voice call to the desired station, and then relying on somebody at that station to hear the call and respond to it. Frequency crowding, radio noise, distance, and poor quality of transmission combined to make communication a difficult task. Changes in communications made a higher quality and more integrated system possible. GMDSS uses a combination of previously used terrestrial radio communications systems and newer satellite communications technology to automate and improve communications for the world’s shipping industry.
  2. PURPOSE: GMDSS is an automated ship-to-shore alerting system that relies on satellite and terrestrial communications links. It is based on the linking of Search and Rescue (SAR) authorities ashore with shipping in the immediate vicinity of a vessel in distress or in need of assistance, so that both land and sea resources can assist in a coordinated SAR operation with minimum.
  3. APPLICABILITY: All ships subject to SOLAS, including all passenger ships, and all cargo ships of 300GT and upwards must meet GMDSS requirements. SOLAS Chapter IV, Regulation 1.
  4. FUNCTIONAL REQUIREMENTS: Ships, while at sea, must be capable of:
  • Transmitting ship-to-shore distress alerts by two separate and independent means using different radiocommunications services;
  • Receiving shore-to-ship distress alerts;
  • Transmitting and receiving SAR coordinating communications;
  • Transmitting and receiving on-scene communications;
  • Transmitting receiving signals for locating;
  • Transmitting and receiving Maritime Safety Information (MSI);
  • Transmitting and receiving general radiocommunications to and from shore-based radio systems or networks; and
  • Transmitting and receiving bridge-to-bridge communications

A ship must not depart from any port unless and until the ship is capable of performing all nine distresses and safety functions in the GMDSS functional requirements.


  1. GENERAL: To meet the nine functional requirements of GMDSS, several pieces of previously  “stand-alone”  equipment have been integrated into one system.

This integrated system is sometimes called the “GMDSSD suite even though some pieces of equipment still stand alone (such as the EPIRBs, SARTs, SCTs,  and some radios).  Several manufacturers of  GMDSS  equipment exist and it is possible to have equipment from several manufacturers contained in a vessel’s GMDSS suite.    The following equipment is included in a standard GMDSS suite:

  • VHF radio /VHF DSC (may be combined): Transmits and receives on VHF frequencies, including required frequencies: 156.3 MHz (channel 6), 156.65 MHz (channel 13), and 156.8 MHz (channel 16). DSC alerting on frequency 156.525 MHz (channel 70) and maintaining a continuous DSC watch on VHF channel 70 is also
  • MF/ HF radio /MF/HF DSC (may be combined): Transmits and receives on MF/HF frequencies including required frequencies: 2182.0 kHz (MF) and working frequencies in the MF and HF bands. DSC alerting on frequencies 2187.5 (MF) and one of five HF DSC frequencies is also required.
  • MF/HF NBDP for follow-on communications after a DSC call, for routine telex communications, and for receiving
  • NAVTEX Receiver: A direct printing service that receives Marine Safety Information (MSI) terrestrial broadcasts containing meteorological and navigational warnings and urgent information to ships in the English language by telex exclusively on 518
  • INMARSAT B: Provides a two-way direct dial telephone and telex from the mobile station (ship) to any location on earth. Fax, e-mail, high-speed computer data, and voice may be transmitted and
  • INMARSAT C: Provides a two-way store and forward message system with small, low-cost terminals. (i.e. laptop computer). This is a text-only system. Text messages, two-way telexes, and low-speed computer data can be transmitted and received. In addition, MSI via Safety Net can be received.


1. Required equipment for GMDSS-equipped ships varies according to GMDSS Sea Area in which the vessel is operating. Sea Areas are as follows:

  • Sea AREA A1: An area within the radiotelephone coverage of at least one VHF coast station in which continuous digital selective calling (DSC) alerting is available
  • Sea AREA A2: An area, excluding sea area A1, within MF radiotelephone coverage of at least one coast station in which continuous digital selective calling is available.
  • Sea AREA A3: An area, excluding sea areas A1 and A2, within the coverage of an INMARSAT satellite in which continuous alerting is available.
  • Sea AREA A4: An area outside sea areas A1, A2, and A3.

2. All ships which are subject to the requirements of SOLAS, regardless of the primary Sea Area of operation are required to have:

3. In addition, when a vessel is operating in Sea Area A1 at times the GMDSS installation should include:

  • A radio installation capable of initiating the transmission of ship-to-shore distress alerts either: whit VHF DSC, a 406 MHz EPIRB, MF DSCD,  or through an INMARSAT terminal capable of two-way communications.
  • VHF radio communications on general  VHF  frequencies,  in addition to those required frequencies for all ships.

4. In addition, when a vessel is operating beyond Sea Area A1, but remaining in Sea Area A2, the GMDSS installation should include:

  • An MF radio installation capable of radiotelephony on frequencies 2182 kHz, and 2187.5 using
  • A radio installation capable of maintaining a continuous DSC watch on 2187.5 (may be combined with MF radio
  • Means of initiating the transmission of ship-to-shore distress alerts by a radio service other than MF, either: 406 MHz EPIRB, on HF DSC, or through INMARSAT
  • Either an MF/HF capable of radiotelephony on working freqs. (ca be combined with the first radio) or an INMARSAT

5. In addition, when a vessel is operating in Sea Area A3, the GMDSS installation should include:

  • An INMARSAT ship on earth
  • An MF/ HF radio capable of radiotelephony on MF/ HF working

6. There are no additional requirements for vessels operating in the sea area


EPIRB: All ships must have a satellite EPIRB capable of transmitting a distress alarm via satellite on the 406 MHz band.

The EPIRB must be installed in an accessible position, ready for either manual release or automatic release and activation in the event that the vessel sinks.

This float-free release and activation occur by means of a hydrostatic Automatic Release Mechanism (ARM) on the EPIRB mounting bracket.

These hydrostatic ARMs have a mandatory replacement date affixed in a conspicuous location, and they must be replaced by this date to ensure proper operation of the EPIRB.

The battery of an EPIRB has an expiration date marked on the outside. The battery must be replaced by this date.

EPIRB: testing is required at various intervals set by the flag state. Tests should be logged.

SART: All vessels must have a 9GHz radar transponder to indicate the location of a distressed vessel by means of a signal sent to a searching vessel’s radar to indicate the presence of an activated SART.

SARTS: are usually carried into a survival craft and activated manually. They must be stowed in such a location that they can be rapidly placed in a survival craft.

The following chart indicates carriage requirements for SARTs:

Survival Craft Transceiver (SCT): All vessels must have two-way VHF transceivers capable of radiotelephone communications between survival craft and rescue units and survival craft and the ship in distress.

These units may be portable or fixed installations within the survival craft.

These units must operate on 156.8 MHz (VHF channel 16) and at least one additional channel.


1. The radio installation must:


The standards put forth in STCW 95 require that “every” person in charge of or performing radio duties on a ship required to participate in the GMDSS shall hold an appropriate certificate related to the GMDSS, issued or recognized by the administration under the provisions of the Radio Regulations” (STCW 95 Reg. IV/2).

The table in STCW A-IV/2 details the performance standards required of a GMDSS operator.

If an onboard maintainer is on the vessel to complete required servicing, he or she must be certified as a GMDSS Maintainer.


1. There are three maintenance options available:

• Duplication of equipment (including antenna)
• Shore-based maintenance
• At-sea maintenance capability (by a licensed at-sea maintainer).

2. Ships sailing in Sea Areas A1 and A2 must be provided with at least one maintenance option.

3. Ships sailing in Sea Areas A3 and A4 must provide at least two maintenance options.


1. All ships should maintain a continuous watch:

• On VHF DSC channel 70 (if fitted with a VHF installation)

• On MF DSC channel 2187.5 kHz (if fitted with an MF installation)

• On HF DSC channels 4207.5 kHz, 6312 kHz, 12577 kHz, or 16804.5 kHz (if fitted with an HF installation) –these frequencies can be monitored on a scanning receiver.

• For satellite shore to ship distress alerts (if fitted with INMARSAT)

• For Marine Safety Information broadcasts (on NAVTEX, HF NBDP, OR INMARSAT Safety Net).

• Does the ship have a valid Ship Safety Radio Certificate supplemented by a Record of Equipment of Radio Facilities?
• Does the vessel have the required GMDSS equipment for its area of operation according to its certificates?
• Are the required numbers of certified GMDSS operators for its area of operation according to its certificates?
• Is there proof of an elected maintenance option (one for the sea are A1 and A2, and two for sea areas A3 and A4)?
• Is the EPIRB stowed in an accessible location where it is permitted to float free in case of sinking?
• Does the vessel have the correct number of SARTs for its size?
• Does the vessel have the correct number of SCTs for its size?



The requirement for GMDSS on passenger vessels and cargo vessels over 300GT was effective as of February 1, 1999. All extensions and waivers have expired, except for those granted on a case-by-case basis because of exceptional circumstances for a single voyage. All vessels subject to SOLAS should be in compliance with the GMDSS regulations, which are found in SOLAS 74/ 78, Chapter IV.

  • GMDSS installations must be inspected by the station license issuing authority every year (periodical survey). During the GMDSS inspection, it is necessary to locate the radio station license to confirm that the equipment on board the vessel conforms to the standard set forth by the issuing authority.


Exam Questions

1. Chapter IV - Radiocommunications of SOLAS Convention is applicable to:

2. The Definitions to ´Sea Area´ include:

4. Every radio installation shall:

6. Satellite EPIRBs shall be annually tested for all aspects of operational efficiency, with special emphasis on checking the emission on operational frequencies, coding and registration, at intervals as specified below:

8. The radio installations of cargo ships shall be subject to the surveys specified below: