GLOBAL MARITIME DISTRESS&SAFETY SYSTEM Pogue Muhone
The basic concept of 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 agency 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.
Components of GMDSS
GMDSS consists of several different safety systems based around different communications technologies.
Click on these hotlinks DSC and NAVTEX There is also an INMARSAT facility we need not know about.
Digital Selective Calling (DSC)
Digital Selective Calling (DSC) is one of the most important parts of GMDSS. DSC provides a means of automating all day-to-day marine terrestrial calling - making marine radio as easy to use as a telephone. DSC effectively provides the operator with a digital dialling system capable of ringing an alarm at a distant radio station when a call is addressed to that station.
Like a telephone, you do not need to know how the call has been routed or even the frequency or channel being used.
All you need is a means of alerting the other party by calling their number, and then a means of talking to them.
Under GMDSS, all vessels are allocated a unique Maritime Mobile Service Identity (MMSI), which is a unique nine digit code. The digital calling information is transmitted on specially designated channels. In the case of a VHF radio, this is Channel 70.
Channel 70 is dedicated for DSC use and must under no circumstances be used for anything else.
An added benefit of DSC is that the digital dialling signal can carry other information, such as your vesselís identity, position and the nature of the call as well as information specifying the channel upon which subsequent communication should take place. The entire message is transmitted in one quick burst, thus reducing the demand time on the calling channel.
In a distress situation, all necessary information is sent automatically at the touch of a single button.
The vesselís position can be determined from a GPS navigation receiver connected to the radio or entered manually. Its identity is permanantly coded into the radio in the form of the vessel's allocated MMSI number. The nature of distress can also be selected by the operator if there is time to do so.
Using digital coding, DSC automates all the radio functions with which existing marine operators are familiar. It also relieves the person at the other end from the tedious task of manual watch-keeping. All the old familiar functions are still in place, but they now have English names and are accesible at the touch of a button.