How GMDSS Work

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GMDSS Station

How GMDSS Working

GMDSS enables a ship which is in distress to send a message in various ways and be virtually certain that it will be heard and acted upon. The distress or safety message is picked up by ships in the area and by shore stations within range if sent on MF and VHF or by shore stations if transmitted using HF, Inmarsat or COSPAS‑SARSAT.

While ships can transmit an alert using any or all of the distress equipment available on board, ships transmit a ship‑to‑ship alert on MF or VHF and a ship‑to‑shore alert in areas A3 or A4, as appropriate, by a ship earth station, HF digital selective calling (DSC) communications or a satellite EPIRB as appropriate.

Ships sailing in area A2 should at least be capable of transmitting a ship‑to‑shore alert on 2,187.5 kHz using DSC and satellite EPIRB and ships sailing in area A1 should at least be capable of transmitting a ship‑to‑shore alert on 156.525 MHz (Channel 70) using DSC.

The system means that distress messages are received much more reliably than before and with the SAR Convention of l979, search and rescue operations are better co‑ordinated. In the event of an incident, the whole operation is co‑ordinated by a designated rescue co‑ordination centre (RCC) which is informed of the alert either through the Inmarsat or COSPAS‑SARSAT systems or from coast radio stations participating in the GMDSS.

The search itself is conducted according to procedures laid down by the SAR Convention and amplified in the IAMSAR manual.

The GMDSS, for its part, provides the means of communications regardless of the area in which the ship is located. For ships equipped with an Inmarsat ship earth station (SES) sending a distress alert is both simple and certain. It only involves pressing a special distress button or using an abbreviated dialling code.

This automatically gives priority access to the system and establishes contact with a coast earth station (CES) via the Inmarsat satellite.

The message automatically gives the ship’s name and position.

The CES, being part of the international search and rescue system, will for its part immediately inform the rescue co‑ordination centre (RCC) located nearest to the ship in distress and thereby initiate a search and rescue operation. Although satellite communications provide a primary means of sending distress messages for ships fitted with an Inmarsat SES, the latter can also use other features of the system if desired ‑ for example they can establish direct contact with an RCC by telex or telephone.

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