Radiocommunication devices are one of the fundamental supports of maritime safety. Since the end of the 19th century this technology has been used to safeguard life at sea, hence its importance is not only for our safety but also for third parties. If all mariners are aware of how communications and GMDSS works, the error margins are reduced when making a rescue or assisting a crew in distress.
From its origin in 1959 the International Maritime Organization (IMO) has strived to safeguard the safety of human life at sea by adopting the highest standards to improve radiocommunications and the Convention on the Safety of Life at Sea (SOLAS) using technological advances in radio devices and ensuring the proper training of radio operators on board.
Thus, in 1979, IMO decided to work on the creation of a new global distress and security system that would also have a properly organized and coordinated structure to carry out Search and Rescue (SAR) operations. In this way the Global Maritime Distress and Safety System (GMDSS) was launched, which began to be implemented in 1992 and entered into force on 1 February 1999, having been adopted by practically all countries with the signing of the SOLAS Convention.
Briefly, how does the GMDSS works?
Radio devices with Digital Selective Call (LSD) have an exclusive transmitter and receiver on the reserved frequencies of 156.525 MHz (VHF channel 70) and 2,187.5 KHz on MF. An alarm is triggered on the device when a DSC call is received.
The device has a red distress button, that when pressed for 5 seconds transmits a DSC distress alert. These alerts are received by all the vessels sailing on proximity and the Maritime Authority, as long as they are within the range of communications. If the radio device is connected to the GPS, the distress alert will indicate the position of the vessel in distress.
Distress alerts should be only sent on situations of serious and imminent danger to the safety of the vessel or persons on board.
There are 4 different categories of GMDSS calls:
Distress: "Mayday" in radiotelephony, it is used to warn of a serious and imminent danger to the safety of a vessel or people when assistance is required immediately. Examples: severe fire on board; sinking; need to abandon the ship; man overboard.
Urgency: "Pan Pan" in radiotelephony, it is used to transmit urgent messages related to the safety of the ship or people when there is no serious or immediate danger. These communications have priority over all communications, except for distress ones. Examples: request of medical assistance for a person seriously injured on board; remain without propulsion in an area of intense maritime traffic.
Security: "Securité" in radiotelephony, it is used to transmit messages related to the safety of navigation or important weather warnings. Examples: reporting light from a buoy that is not working or out of position; warn of sighting of large drifting ice formations or of a dangerous element floating in the sea; give a temporary warning.
Routine: used to establish communication with another station on a working channel.
When the Digital Selective Call is used, a transmission is normally performed in two phases: The first phase includes the transmission of the digital call and the second, the transmission by radiotelephony of the message.
Tips for proper use of radio equipment
- Inform your crew and guests of the importance of radio device and prevent them from being manipulated incorrectly.
- Children should not be able to handle the radio without the supervision of an adult.
- A false alarm can trigger a SAR operation that, in addition to human and economic effort, can divert essential resources for a real emergency that may occur.
- Be especially respectful on the call and distress channel (Channel 16 in VHF).
- Never transmit a DSC alarm to test the radio. Uses the test mode provided by the manufacturer (TEST button/option).
- Regularly check with a friend about the quality of your transmission and reception.
- Your GPS navigator must be correctly connected to the radio so that, in case of emergency, your position is transmitted and the search is effective.
- You must obtain training to operate your VHF DSC radio station correctly.
- Keep the radio always on while you are at sea, so it will maintain permanent listening on the DSC distress frequencies and will be ready for use if required.