It is supplemental to the International Convention on Maritime Search and Rescue (ICMSaR) adopted in 1979 and provides basis for the communication.
[1]: 1 [2] GMDSS consists of several systems which are intended to perform the following functions: alerting (including position determination of the ship in distress) ships in the vicinity and ashore authorities,[1]: 1 search and rescue coordination, locating (homing), maritime safety information broadcasts, general communications, and bridge-to-bridge communications.
This group also passed a resolution calling for development by IMO of a Global Maritime Distress and Safety System (GMDSS) to provide the communication support needed to implement the search and rescue plan.
The GMDSS provides for automatic distress alerting and locating in cases where a radio operator does not have time to send an SOS or MAYDAY call, and, for the first time, requires ships to receive broadcasts of maritime safety information which could prevent a disaster from happening in the first place.
In 1988, IMO amended the Safety of Life at Sea (SOLAS) Convention,[5] requiring ships subject to it to fit GMDSS equipment.
The main types of equipment used in GMDSS are: Cospas-Sarsat is an international satellite-based search and rescue system, established by Canada, France, the United States, and Russia.
These four countries jointly helped develop the 406 MHz Emergency Position-Indicating Radio Beacon (EPIRB), an element of the GMDSS designed to operate with Cospas-Sarsat system.
The certification of Iridium in 2020 ended a monopoly on the provision of the satellite-based portion of maritime distress services that had previously been held by Inmarsat since the system became operational in 1999.
Fleet 77 fully supports the Global Maritime Distress and Safety System (GMDSS) and includes advanced features such as emergency call prioritisation.
SSAS provides a means to covertly transmit a security alert distress message to local authorities in the event of a mutiny, pirate attack, or other hostile action towards the vessel or its crew.
Worldwide broadcasts of maritime safety information can also be made on HF narrow-band direct printing channels.
The GMDSS installation on ships include one (two on vessels over 500 GT) search-and-rescue locating device called Search and Rescue Radar Transponders (SART) which are used to locate survival craft or distressed vessels by creating a series of twelve dots on a rescuing ship's 3 cm radar display.
Once detected by radar, the Search and Rescue Locating device will produce a visual and aural indication to the persons in distress.
The IMO also introduced digital selective calling (DSC) on MF, HF and VHF maritime radios as part of the GMDSS system.
IMO and ITU both require that the DSC-equipped MF/HF and VHF radios be externally connected to a satellite navigation receiver (GPS).
IMO and the USCG also plan to require ships carry a Universal Shipborne automatic identification system, which will be DSC-compatible.
GMDSS equipment is required to be powered from three sources of supply: The batteries are required to have a capacity to power the equipment for 1 hour on ships with an emergency generator or built prior to February 1995, and 6 hours on ships not fitted with an emergency generator or built after February 1995 in order to comply with SOLAS.
Changeover from AC to battery supply must be automatic, and effected in such a way that any data held by the equipment is not corrupted ("no break").
During Coast Guard inspections, the batteries must be able to go from 100% discharge to fully charged in no longer than 10 hours in order to pass certification.
Storage batteries provided as a reserve source of energy must be installed in accordance with applicable electrical codes and good engineering practice.
Prior to the GMDSS, the number and type of radio safety equipment ships had to carry depended upon its tonnage.
U.S. ships whose voyage allows them to always remain within VHF channel 16 coverage of U.S. Coast Guard stations may apply to the Federal Communications Commission for an individual waiver to fit to Sea Area A1 requirements.
Similarly, those who remain within 2182 kHz coverage of U.S. Coast Guard stations may apply for a waiver to fit to Sea Area A2 requirements.
However, to obtain this certificate an applicant must also hold a General radiotelephone operator license (GROL), which requires passing commercial written exam elements 1 and 3 (and thus supersedes the MROP).
Upon the further passing of optional written exam element 8 the ship radar endorsement will be added to both the GROL and Maintainer licenses.
[13] Since an older certificate does show an expiration date, for crewmembers sailing internationally it may be worth paying the fee (as of 2010 it was $60) to avoid any confusion with local authorities.
Finally, to actually serve as a GMDSS operator on most commercial vessels the United States Coast Guard requires additional classroom training and practical experience beyond just holding a license.