The Global Maritime Distress and Safety System (GMDSS) means important technological progress in radiocommunications in order to achieve an effective, fast and viable system to handle maritime distress and safety communications.

The system,considers the integration of different communication services, even simultaneously, in order to reduce the uncertainty of the abscence of a link through just one mean. The normalization of the information contained in the distress and safety messages provides the necessary data for the precise localization of the damaged vessel and for aid and rescue tasks. Simplification and automatization of the procedure for the generation of distress and safety calls. Provide a world-wide cover for the reception of alerts. This way, we would replace the traditional methods of MORSE and radiotelephony, which have demonstrated and justified their use in a number of occasions, but still manifested their numerous imperfections as they are subject to reception uncertainty and involuntary human error.

As part of the GMDSS and for the communication systems in VHF, MF and HF, Digital Selective Calling has been defined. This is an automatic calling system for ship-shore, shore-ship or ship-ship alerts.

Due to the limited range of each of the radio communication systems, several operation and cover areas have been defined:

  • A1- Zone near the coast with VHF-DSC coverage (approx. 25-30 miles).
  • A2- Navigation zone with MF-DSC coverage, excluding zone A1 (approx. 250 miles).
  • A3- Navigation zone excluding zones A1, A2 and the polar regions (> 70°), with HF-DSC And INMARSAT coverage.
  • A4- Polar zones, >70°N, >70°S.

Therefore the communication services that make a complete GMDSS system in a ship are:

  • Radio range beacon for damaged vessel localization.
  • Radar transponder (SART).
  • NAVTEX Transmitter.
  • VHF portables.
  • VHF radio station with DSC.
  • HF radio station with DSC..
  • MF radio station with DSC.

INVELCO, S.A., is the design leader of communications equipment addressed to (GMDSS). It is manufacturer of all the equipment that usually set a system of these characteristics.

INVELCO, S.A., has designed, installed and started all the Global Maritime Distress and Safety System operating in Spain for the Merchant Marine Administration.

imagen 1 2x - Maritime Safety Compliance

As it was previously mentioned, Digital Selective Calling DSC is part of the G.M.D.S.S. and it is used in this system mainly as an automatic calling system for distress alerts from ships and for the acknowledgment of receipt of the corresponding coastal stations. It can also be used by the ships and the coast stations for distress alert relays and any type of urgent and safety marine calls.

In general, it can be said that the use of a DSC call will be part of a procedure with the following sequence of processes. In the first place a notice is generated by means of DSC. Next, an acknowledgment of receipt is produced by the destination of the notice, in case when this is necessary and by the same DSC system. Finally communication is established through a radiotelephony channel, associated to the DSC channel, or through the channel/frequency and mode specified in the previous DSC communications.