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Basic Concepts of the GMDSS

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What is GMDSS? The Global Maritime Distress and Safety System (GMDSS) is all about maritime safety at sea. Overall, GMDSS creates a standardized system for communication and safety at sea, helping to save lives and prevent maritime disasters.

This article of a GMDSS, explaining its importance, components, and how it ensures safety for crews navigating.

Functional requirements

The GMDSS regulations (chapter IV of the International SOLAS Convention), require that every GMDSS equipped ship shall be capable of:

  • transmitting ship-to-shore Distress Alerts by at least two separate and independent means, each using a different radio communication service;
  • 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 receiving locating signals;
  • receiving maritime safety information;
  • transmitting and receiving general radio communications relating to the management and operation of the vessel;
  • transmitting and receiving bridge-to-bridge communications.

Application

The GMDSS applies to vessels subject to the SOLAS Convention – that is:

Commercial vessels of 300 Gross Registered Tons (GRT) and above, engaged on international voyages.

The GMDSS became mandatory for such vessels as at February 1, 1999.

Commercial vessels under 300 GRT, or those above 300 GRT engaged on domestic voyages only are subject to the requirements of their Flag State – Definition and PronunciationFlag State. Some Flag States have incorporated GMDSS requirements into their domestic marine radio legislation – however many have not.

Equipment and Operational requirements GMDSS zones

The major difference between the GMDSS and its predecessor systems is that the radio communications equipment to be fitted to a GMDSS ship is determined by the ship’s area of operation, rather than by its size.

Because the various radio systems used in the GMDSS have different limitations with regards to range and services provided, the new system divides the world’s oceans into 4 areas:

  • Area A1 lies within range of shore-based VHF coast stations (20 to 30 nautical miles);
  • Area A2 lies within range of shore based MF coast stations (excluding A1 areas) (approximately 100 – 150 nautical miles);
  • Area A3 lies within the coverage area of INMARSAT communications satellites (excluding A1 and A2 areas – approximately latitude 70 degrees north to latitude 70 degrees south);
  • and Area A4 comprises the remaining sea areas outside areas A1, A2 and A3 (the polar regions).

GMDSS communication systems

The GMDSS utilises both satellite and terrestrial (i. e.: conventional) radio systems.

Sea Area A1 requires short range radio services – VHF is used to provide voice and automated distress alerting via Digital Selective Calling (DSC).

Sea Area A2 requires medium range services – Medium Frequencies (MF – 2 MHz) are used for voice and DSC.

Sea Areas A3 and A4 require long range alerting – High Frequencies (HF – 3 to 30 MHz) are used for voice, DSC and Narrow Band Direct Printing (NBDP – radio telex).

Read also: Personal health and safety crew members on board a gas carrier

Equipment requirements vary according to the area the ship is trading to or through. Accordingly, it is quite possible that a small 300 ton cargo vessel may carry the same amount of communications equipment as a 300 000 ton oil tanker, if they are both operating in the same area….this is a marked change from the pre-GMDSS systems.

This is illustrated in the diagram below:

The GMDSS Concept
Fig. 1 Global Maritime Distress and Safety SystemConcept

GMDSS operational requirements

General

The GMDSS enables a ship in distress to send an alert using various radio systems. These systems are designed such that the alert has a very high probability of being received by either shore rescue authorities and/or other vessels in the area.

Equipment performing GMDSS functions must be simple to operate and (wherever appropriate) be designed for unattended operation.

Distress Alerts must be able to be initiated from the position from which the ship is normally navigated (i. e. the bridge).

EPIRBs are required to be installed close to, or capable of remote activation from the position from which the ship is normally navigated.

Equipment to be carried

The SOLAS GMDSS regulations are structured such that all GMDSS ships are required to carry a minimum set of equipment, with (basically) more equipment being required the further the ship travels from land.

The SOLAS GMDSS regulations do not make particularly easy reading – a simplified version of the equipment required to be carried for each sea area is detailed below.

Minimum requirements

GMDSS ships are required to carry the following minimum equipment:

  • A VHF radio installation capable of transmitting DSC on channel 70, and radiotelephony on channels 16, 13 and 6.
  • One SART if under 500 GRT, 2 SARTs if over 500 GRT.
  • Two portable VHF transceivers for use in survival craft if under 500 GRT, three if over 500 GRT.
  • A NAVAREA receiver, if the ship is engaged on voyages in any area where a NAVTEX service is provided.
  • An Inmarsat EGC receiver, if the ship is engaged on voyages in any area of Inmarsat coverage where MSI services are not provided by NAVTEX or HF NBDP (see note 1).
  • A 406 MHz or 1,6 GHz EPIRB.

Note 1 – in practice, this means that all GMDSS A3 and A4 vessels are required to carry at least one Inmarsat C system.

Radio equipment – Sea area A1

Every ship engaged on voyages exclusively in sea area A1 shall be provided with the minimum equipment specified previously, with the option to replace the 406 EPIRB with a VHF DSC EPIRB.

VHF Radiotelephone
Fig. 2 Very high frequency Radiotelephone

Radio equipment – Sea areas A1 and A2

Every ship engaged on voyages beyond sea area A1, but remaining within sea area A2, shall be provided with the minimum equipment specified previously, plus:

  • An MF radio installation capable of transmitting and receiving on the frequencies 2 187,5 kHz using DSC and 2 182 kHz using radiotelephony;
  • a DSC watchkeeping receiver operating on 2 187,5 kHz;
  • A 406 MHz EPIRB.

The ship shall, in addition, be capable of transmitting and receiving general radiocommunications using radiotelephony or direct-printing telegraphy by:

  • A HF radio installation operating on working frequencies in the (marine) bands between 1,605 kHz and 27 500 kHz. (This requirement is normally fulfilled by the addition of this capability in the MF equipment referred to earlier).

Radio equipment – Sea areas A1, A2 and A3

These vessels have two options to satisfy their GMDSS carriage requirements and basic provisionsGMDSS requirements. The options allow a vessel to choose from the primary method to be used for ship-shore alerting.

Typical GMDSS A2 station
Fig. 3 Typical Global Maritime Distress and Safety System A2 station

Every ship engaged on voyages beyond sea areas A1 and A2, but remaining within sea area A3 shall be provided with the minimum equipment specified previously, plus either:

  • An Inmarsat C ship earth station:
  • An MF radio installation and 2 187,5 kHz DSC watchkeeping receiver;
  • A 406 MHz EPIRB.

or

  • An MF/HF radio installation capable of transmitting and receiving on all distress and safety frequencies in the (marine) bands between 1 605 kHz and 27 500 kHz: using DSC, radiotelephony;
  • and NBDP An MF/HF DSC watchkeeping receiver capable of maintaining DSC watch on 2 187,5 kHz, 8 414,5 kHz and on at least one of the distress and safety DSC frequencies 4 207,5 kHz, 6 312 kHz, 12 577 kHz or 16 804,5 kHz; at any time, it shall be possible to select any of these DSC distress and safety frequencies;
  • A 406 MHz EPIRB;
  • An INMARSAT ship earth station.

In addition, ships shall be capable of transmitting and receiving general radiocommunications using radiotelephony or direct-printing telegraphy by an MF/HF radio installation operating on working frequencies in the (marine) bands between 1 605 kHz and 27 500 kHz. This requirement is normally fulfilled by the addition of this capability in the MF/HF equipment referred to earlier.

 GMDSS station
Fig. 4 Typical GMDSS A3 station

In practice, MF only transceivers are not produced – all marine MF radio equipment is also fitted with HF facilities.

Radio equipment – Sea areas A1, A2, A3 and A4

In addition to carrying the equipment listed previously, every ship engaged on voyages in all sea areas shall be provided with:

  • An MF/HF radio installation as described earlier;
  • An MF/HF DSC watchkeeping receiver as described earlier;
  • A 406 MHz EPIRB.

In addition, ships shall be capable of transmitting and receiving general radiocommunications using radiotelephony or direct-printing telegraphy by an MF/HF radio installation as described earlier.

Means of ensuring availability of ship station equipment

Regulation 15 of the SOLAS GMDSS regulations defines 3 methods to ensure availability of GMDSS equipment at sea:

  • at sea electronic maintenance, requiring the carriage of a qualified radio/electronic officer (holding a GMDSS First or Second class Radio-Electronics Certificate) and adequate spares and manuals;
  • duplication of certain equipment;
  • or shore based maintenance.

Ships engaged on voyages in sea areas A1 and A2 are required to use at least one of the three maintenance methods outlined above, or a combination as may be approved by their administration. Ships engaged on voyages in sea areas A3 and A4 are required to use at least two of the methods outlined above.

And of course what all that means is that 99 % of A3 GMDSS ships, along with probably 100 % of A1 and A2 GMDSS ships do not opt for at sea maintenance – they either duplicate the equipment and use shore based maintenance (for A3 ships), or use shore based maintenance only (A1 and A2 ships).

Equipment to be duplicated for area A3 vessels

GMDSS ships operating in A3 areas are required to provide the following duplicated equipment:

  • two complete VHF installations (including DSC), and either;
  • two complete INMARSAT C systems and one MF radio system;
  • or one complete Inmarsat C system and one complete MF/HF radio system (including a scanning DSC receiver and NBDP equipment).

Many GMDSS ships opt for the latter option (1 INMARSAT C and one MF/HF DSC system), on cost grounds. Unfortunately, this has proven to be one of the underlying causes of the present extremely high false alerting rate on some GMDSS systems.

Power supply requirements

GMDSS equipment is required to be powered from three sources of supply:

  • ship’s normal alternators/generators;
  • ship’s emergency alternator/generator (if fitted);
  • and a dedicated radio battery supply.

The batteries are required to have a capacity to power the equipment for 1 hour on ships with an emergency generator, and 6 hours on ships not fitted with an emergency generator.

The batteries must be charged by an automatic charger, which is also required to be powered from the main and emergency generators.

Changeover from AC to battery supply must be automatic, and effected in such a way that any any data held by the equipment is not corrupted (i. e. : “no break“).

Operator qualifications

There are a number of different types of GMDSS qualifications, as follows:

  • second Class Radio-Electronic Certificate;
  • and GMDSS General Operator’s Certificate

The First and Second Radio-Electronic Certificates are diploma and associate diploma level technical qualifications. They are designed for Ship’s Radio-Electronic Officers, who sail on GMDSS ships which use the option of at-sea electronic maintenance.

The GMDSS General Operator’s Certificate is a operator qualification, designed for Navigating Officers.

Survival Craft Radio Equipment

Search And Rescue (Radar) Transponders (SARTs)

SART is a self contained, portable and buoyant Radar Transponder (receiver and transmitter).

SARTs operate in the 9 GHz marine radar band, and when interrogated by a searching ship’s radar, respond with a signal which is displayed as a series of dots on a radar screen.

SAR-16 AIS SART
Fig. 5 Search and rescue radar transponder

Although SARTs are primarily designed to be used in lifeboats or liferafts, they can be deployed on board a ship, or even in the water.

SARTs are powered by integral batteries which are designed to provide up to 96 hours of operation.

Operation

When activated, a SART responds to a searching radar interrogation by generating a swept frequency signal which is displayed on a radar screen as a line of 12 dots extending outward from the SARTs position along its line of bearing.

The spacing between each dot is 0,6 nautical miles.

As the searching vessel approaches the SART, the radar display will change to wide arcs. These may eventually change to complete circles as the SART becomes continually triggered by the searching ship’s radar.

SART signal
Fig. 6 SART signal on radar display

Although not an actual SART response, this radar picture gives an impression of how a SART signal would be displayed.

Some slight position error will also be caused by the SART switching from receive to transmit mode.

SARTs will also provide a visual and audible indication to users when interrogated by a searching radar.

Range

The range achievable from a SART is directly proportional to its height above the water. A SART mounted at 1 m (i. e.: in a liferaft) should be able to be detected at 5 nautical miles by a ship’s radar mounted at 15 m.

The same SART should be able to be detected at 30 nautical miles by an aircraft flying at 8 000 feet.

GMDSS carriage requirements

GMDSS vessels from 300 to 500 GRT are required to carry 1 SART, and vessels over 500 GRT are required to carry 2.

Portable VHF transceivers

These units are designed to allow communications between searching vessels and survivors in liferafts.

VHF portable transceivers
Fig. 7 Typical GMDSS VHF portable transceivers

They operate on the VHF marine band in voice mode. DSC capability is not fitted.

Performance standards

The IMO performance standard requires that the equipment:

  • provide operation on VHF channel 16 (the radiotelephone distress and calling channel) and one other channel;
  • be capable of operation by unskilled personnel;
  • be capable of operation by personnel wearing gloves;
  • be capable of single handed operation, except for channel changing;
  • withstand drops on to a hard surface from a height of 1 metre;
  • be watertight to a depth of 1 metre for at least 5 minutes, and maintain watertightness when subjected to a thermal shock of 45 degrees Celsius.
  • not be unduly effected by seawater or oil;
  • have no sharp projections which could damage survival craft;
  • be of small size and weight;
  • be capable of operating in the ambient noise level likely to be encountered on board survival craft;
  • have provisions for attachment to the clothing of the user;
  • be either a highly visible yellow/orange colour or marked with a surrounding yellow/orange marking strip;
  • be resistant to deterioration by prolonged exposure to sunlight.

GMDSS carriage requirements. GMDSS vessels from 300 to 500 GRT are required to carry 2 VHF portables, and vessels over 500 GRT are required to carry 3.

Author
Author photo - Olga Nesvetailova
Freelancer
Literature
  1. General operator’s Certificate for The Global Maritime Distress and Safety System, Course + Compendium, Model Course IMO 1.25, Printed by PMS UK Ltd London, 2004.
  2. European Radiocommunications Committee ERC Decision of 10 March 1999 on the harmonised examination syllabi for General Operator’s Certificate (GOC) and Restricted Operator’s Certificate (ROC)(ERC 99 01).
  3. IMO GMDSS-Handbook, London, U. K., 2004.
  4. Norcontrol Capella GMDSS Simulator, Technical documentations, Kongsberg Maritime Ship Systems, Norway, 2005.
  5. INMARSAT MARITIME COMMUNICATIONS HANDBOOK – INMARSAT – London, U. K, 2005.
  6. Seafarers’ Training, Certification and Watchkeeping CODE 1995 (STCW Code 95, published by IMO, London, 1996), – Part A Mandatory standards regarding provisions of the annex to the Convention Chapter IV Standards regarding radio personnel.
  7. Seafarers’ Training, Certification and Watchkeeping CODE 1995 (STCW Code 95, published by IMO, London, 1996), – Part B Mandatory guidance regarding provisions of the STCW and its annex; Chapter IV Guidance regarding radiocommunication and radio personnel.
  8. V. Pipirigeanu, M. Udrea, Introducere in GMDSS – Sistemul Mondial de Primejdie si Siguranta Maritima, Ed. Europolis, Constanta, 2002.
  9. Graham D. Lees, William G. Williamson, Handbook for Marine Radio Comunication, e d. LLOYD S OF LONDON PRESSLTD., 2004.
  10. ITU Manual for Use by The Maritime Mobile and Maritime Mobile Satellite Services, 2006.
  11. IAMSAR Manual – International Aeronautical and Maritime Search and Rescue Manual, 2001.
  12. C/S G.003 – Introduction to Cospas-Sarsat System, (G3OCT28.99D Issue 5 – Rev 1 October 1999), C/S Documents published by Cospas-Sarsat in Handbook of Regulations on 406 MHz and 121,5 MHz Beacons, (1999);
  13. Tor R. Kristensen – An Introduction to GMDSS, revised GOC Edition, – 7th edition, Leknes, Norway, 2007.
  14. C/S T.001 – Specification for Cospas-Sarsat 406 MHz Distress Beacon, (T1OCT30.99D – Issue 3-Rev. 2 October 1999), Documents published by Cospas-Sarsat in Handbook of Regulations on 406 MHz and 121,5 MHz Beacons (1999).
  15. IMO SOLAS (SAVE OF LIVE AT SEA), Consolidated Edition, London, 2001.

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