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PART - 2 Basic concept of the GMDSS
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2.1 General
2.1.1 The basic concept of the GMDSS is that search and rescue authorities ashore, as well as shipping in the immediate vicinity of the ship in distress, will be rapidly alerted to a distress incident so that they can assist in a co-ordinated SAR operation with the minimum delay. The system also provides for urgency and safety communications and the promulgation of maritime safety information (MSI) - navigational and meteorological warnings and forecasts and other urgent safety information to ships. In other words, every ship is able, irrespective of the area in which it operates, to perform those communication functions which are essential for the safety of the ship itself and of other ships operating in the same area.
2.1.2 Recognizing that the different radio subsystems incorporated in the GMDSS system have individual limitations with respect to the geographical coverage and service provided, the equipment required carried by a ship is determined in principle by the ship's area of operation. Which is designated as follows (regulation IV/2.1.12-2.1.15): |
- Sea area A1 - an area within the radiotelephone coverage of a least one VHF coast station in which continuous digital selective calling (DSC) alerting is available, as may be defined by a Contracting Government;
� Sea area A2 - as area, excluding sea area A1, within the radiotelephone coverage of a least one MF coast station in which continuous DSC alerting is available, as may be defined by a Contracting Government;
� Sea area A3 - an area, excluding sea areas A1 and A2, within the coverage of an INMARSAT geostationary satellite in which continuous alerting is available; and
� Sea area A4 - an area outside sea areas A1, A2 and A3. In all areas of operation the continuous availability of alerting is required. Criteria for establishing those GMDSS sea areas are given in annex 2-12 (resolution A.704(17)).
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2.2 Communications functions in the GMDSS
The GMDSS comprises the following communications functions as required by regulation IV/4. These functions are individually performed by the radio subsystems set out in part 3. |
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Alerting (regulation IV/4.1.1-4.1.3)
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2.2.1 Distress alerting is the rapid and successful reporting of a distress incident to a unit which can provide or co-ordinate assistance, as prescribed in RR N3112 . This would be rescue co-ordination centre (RCC) on another ship in the vicinity. When an alert is received by an RCC, normally via a coast station or coast earth station, the RCC will relay the alert to SAR units and to ships in the vicinity of the distress incident. A distress alert should indicate the ship's identification and the position of the distress and, where practicable, its nature and other information which could be used for rescue operations (RR N3113*).
2.2.2 The communication arrangements under the GMDSS are designed to enable distress alerting to be performed in all three directions - ship-to-shore, ship-to-ship and shore-to-ship - in all sea areas (regulation IV/4.1.1-4.1.3). The alerting function is based on both satellite and terrestrial means and the initial distress alert is primarily transmitted in the ship-to-shore direction. When the distress alert is transmitted by DSC on VHF, MF or HF, ships within DSC range of the ship in distress will also be alerted (ship-to-ship alerting).
2.2.3 A distress alert is normally initiated manually and all distress alerts are acknowledged manually. When a ship sinks, a float-free satellite emergency position-indicating radio beacon (EPIRB) is automatically activated. Ships operating exclusively in sea area A1 may, in lieu of satellite EPIRBs, use VHF EPIRBs on channel 70.
2.2.4 The relaying of a distress alert from an RCC to ships in the vicinity of a distress incident is made by satellite communication or by terrestrial communication using appropriate frequencies. In either case, to avoid all ships in a large sea area being alerted, an "area call" is normally transmitted so that only those ships in the vicinity of the distress incident are alerted. On receipt of relayed distress alert, ships in the area addressed are required to establish communication with the RCC concerned to enable the assistance to be co-ordinated. Parts 5 and 6 deal with the operational procedure and routeing of the distress alert. |
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SAR co-ordinated communications (regulation IV/4.1.4)
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2.2.5 In general these are the communications necessary for the co-ordination of ships and aircraft participating in a search and rescue operation following a distress alert and include communications between RCCs** and any "on-scene commander (OSC)"*** or "co-ordinator surface search (CCS)"*** in the area of the distress incident.
2.2.6 The SAR operations messages are transmitted in both directions, as distinct from "alerting", which is generally the transmission of a specific message in one direction only, and distress and safety traffic by radiotelephony and direct-printing telegraphy will normally be used for passing such messages.
2.2.7 The techniques which are available for SAR co-ordinating communications are radiotelephony or direct-printing telegraphy or both. These communications can be carried out by terrestrial or satellite means, dependent upon the equipment fitted on the ship and the sea area in which the incident occurs. |
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On-scene communications (regulation IV/4.1.5)
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| 2.2.8 On-scene communications normally take place in the MF and VHF bands on frequencies designated for distress and safety traffic (given in annex 9.3), by radiotelephony or direct-printing telegraphy. These communications between the ship in distress and assisting units relate to provision of assistance to the ship or the rescue of survivors. When aircraft are involved in on-scene communications they are normally able to use 3023, 4125 and 5680 kHz. In addition, SAR aircraft can be provided with equipment to communicate on 2182 kHz or 156.8 MHz or both, as well as on other maritime mobile frequencies. |
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Locating (regulation IV/4.1.6)
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| 2.2.9 Locating is the finding of a ship/aircraft in distress or its survival craft or survivors, as defined by regulation IV/2.1.8. In the GMDSS this function is performed by means of 9 GHz SAR radar transponders (SARTs) by the ship in distress or survivors, whose position is indicated when the SART is interrogated by the searching unit's 9 GHz radar. Use of the frequency 121.5 MHz in most satellite EPIRBs is provided for homing by aeronautical SAR units. |
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Promulgation of MSI (regulation IV/4.1.7)
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| 2.2.10 Ships need to be provided with up-to-date navigational warnings and meteorological warnings and forecast and other urgent safety information (MSI). MSI is made available by narrow-band direct-printing telegraphy broadcasts, using forward error correction on the frequency 518 kHz (international NAVTEX service - regulation 2.1.7) and, for ships which navigate beyond the NAVTEX coverage, by broadcasts via the INMARSAT enhanced group call (EGC) system (known as the international SafetyNET system). A high seas MSI broadcast system by HF direct-printing telegraphy is under development. Details for MSI systems are given in section 3.7. |
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General radiocommunications (regulation IV/4.1.8)
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| 2.2.11 General radiocommunications in the GMDSS are those communications between ship stations and shore-based communication networks which concern the management and operation of the ship and may have an impact on its safety (regulation IV/2.1.5). These communications can be conducted on any appropriate channel, including those used for public correspondence. Examples are orders for pilot and tug services, chart replacement, repairs, etc. |
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Bridge-to-bridge communications (regulation IV/4.1.9)
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| 2.2.12 Bridge-to-bridge communications are inter-ship safety communications conducted from the position from which the ship is normally navigated (regulation IV/2.1.1), normally performed by VHF radiotelephony. |
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* - See annex 9.3
** - They are defined in the 1979 SAR Convention annex, chapter I
.*** - See regulation IV/7.1.5 and annex 2-14, paragraph 3.5. See also annexes 3-5-3, 3-5-4 and 3.5.6. |
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