Things You Should Know About Global Maritime Distress and Safety System (GMDSS)
In the 18th century, ships sailing in international and coastal waters relied on Morse code to send distress signals to coastal authorities or nearby ships in the event of emergencies.
As such, messages were transmitted as text messages via tones or lights, but they were not clear enough for shipboard personnel to identify the type of emergency.
Therefore, the International Maritime Organization (IMO) adopted an internationally recognized safety procedure, GMDSS – Global Maritime Distress and Safety System, under Chapter IV of the International Convention for the Safety of Life at Sea (SOLAS).
GMDSS and its uses
GMDSS became fully implemented on 1 February 1999. The system sets standards for communication protocols, procedures, and safety equipment used by ships in distress.
Under the Global Maritime Distress and Safety System (GMDSS), all passenger and cargo ships sailing in international waters with a gross tonnage of more than 300 tons must be equipped with equipment that complies with the system.
When a ship uses the GMDSS system, it sends distress signals via satellite or radio communication equipment. In addition to serving as a general communication channel, the system also functions as a means of exchanging maritime safety information.
In the GMDSS system, the sea area is divided into distinct areas based on the distribution of operating equipment. They are as follows:
- Area Frequency Band Equipment
- A1: 20 to 50 meters (VHF DSC)
- A2: 50 to 400 meters (VHF + MF)
- A3: 70°N to 70°S (VHF + MF) + one INMARSAT equipment
- A4: 70°N or above 70°S (HF + MF + VHF)
To better understand the above table, the frequency ranges within a particular band are listed below:
- MF: 300 kHz to 3 MHz
- HF: 30 MHz to 30 MHz
- VHF: 30 MHz to 300 MHz
VHF (VHF)
The 156 MHz to 174 MHz band is allocated for maritime communications. Channel 16 (set to 156800 MHz) is reserved for distress, emergency, and safety communications. Channel 70 is set at 156.525 MHz for routine VHF DSC communications.
Guard channels are set above and below channel 16 to avoid interference. If other communications, except for distress, safety, and emergency communications, are interfered with, smooth communication on channel 16 cannot be guaranteed. Therefore, the guard channel frequencies are 156.775 MHz and 156.825 MHz.
Additionally, the VHF band is powered by a 24 V DC power supply. Radio communications utilize J3E transmission, while VHF DSC communications employ G2B transmission.
The various components of the Global Maritime Distress and Safety System (GMDSS) are as follows:
International Maritime Satellite Organization (INMARSAT):
A satellite-based system that includes ship-borne ground stations – Inmarsat B, C, and F77. It provides ship-to-ship, ship-to-shore, and shore-to-ship telex, telephone, and data transmission services, as well as priority telex and telephone services connected to shore rescue centers.
NAVTEX:
The NAVTEX system is an internationally recognized automated system for distributing maritime safety information (MSI), including weather forecasts and warnings, navigational warnings, search and rescue (SAR) notices, and other similar safety information.
Emergency Position Indicating Radio Beacon (EPIRB):
An EPIRB is a device used to assist in locating survivors during search and rescue operations. It is an adjunct to the distress signal. Click here to learn about EPIRBs.
Search and rescue locating equipment: Primarily a search and rescue radar transceiver. This equipment is used to guide search and rescue units to the location of distress and to transmit distress signals when queried. Click here to learn about search and rescue equipment.
Digital Selective Calling (DSC):
A communications service provided between ships, between ships and shore, or between shore and ship, providing safety and distress information primarily on high or medium frequencies and marine very high frequency (VHF) frequencies.
Documents required for GMDSS on board:
- Ship Radio License
- Radio Operator Certificate
- Radio Safety Certificate
- GMDSS Radio Register
ITU List of Base Station Signals and Digital Identifications used by Maritime Mobile and Maritime Mobile Satellite Services
- ITU List of Coast Stations
- ITU List of Ship Stations
- ITU List of RFID Stations and Special Service Stations
- Antenna Equipment Diagram
- Valid Shoreline Maintenance Certificate
GMDSS Training
Operating GMDSS equipment requires approved training and a license issued by the communications department of the administration. A driver needs to hold a General Operator Certificate (GOC) to operate GMDSS equipment on board a ship.
To obtain this certification, you must attend a short course and pass written and oral examinations. This training is designed for students who must hold a radio operator’s license and are authorized to operate all equipment in accordance with the Global Maritime Distress and Safety System (GMDSS) regulations.
The course takes approximately 12 days. As the course is mandatory, it is recommended that you register in advance with the certifying body to reserve a seat later. Depending on your country, please visit the certifying body’s website and the Ministry of Shipping’s website (or the corresponding ministry in your country) for complete information on the GMDSS course requirements and entry criteria.
During the course, the officer will learn all aspects of the GMDSS, from radio signal recording to INMARSAT information transmission, as well as all aspects required for onboard communications. The written examination assesses the theoretical part, while the oral examination is a one-on-one interview with an inspector who evaluates the student’s knowledge of all aspects of the GMDSS, encompassing the entire syllabus (both theoretical and practical).
UK List of Naval Radio Signals (ALRS) Volume 5:
NP285 or ALRS Volume 5 is a publication containing comprehensive theoretical and practical information on all matters relating to the Global Maritime Distress and Safety System (GMDSS). Relevant corrections can be found in the Weekly Notices to Mariners (NTM) Part 6. It includes:
- Distress communications and false alarms
- Digital Direct Calling (DSC) equipment operating procedures
- Search and rescue transceivers
- Extracts from the International Telecommunication Union Radio Regulations
- List of VHF Coast DSC stations in A1 marine area
- List of VHF Coast DSC stations in A2 marine area
- List of VHF Coast DSC stations in A3 marine area
- International Maritime Satellite Organization (INMARSAT)
- Maritime Safety Information (MSI)
- SafetyNet
- NAVTEX
- Distress, search and rescue
Portable maritime radio
The portable maritime transceiver, also known as a lifeboat transceiver, is a crucial component of the Global Maritime Distress and Safety System (GMDSS). It is a device placed in the wheelhouse for use when ship personnel need to board a lifeboat and can also be used for onboard communications.
Jotron TX indicator
In emergency situations, it is used for on-site coordination between lifeboats and search and rescue units. The International Maritime Organization (IMO) requirements for lifeboat transceivers are as follows:
- Can be operated by non-professionals.
- Transmit and receive on 156.8 MHz (16 channels) and 156.3 MHz (6 channels).
- The devices can withstand a drop from a height of one meter.
- Can withstand 5 minutes underwater4 at a depth of one meter.
- Minimum power: 0.25 watts.
- Equipped with a power reduction switch.
- The antenna must be omnidirectional and vertically polarized.
- Battery life must be at least 8 hours (NiCd or Li-ion).
The scope of the Global Maritime Distress and Safety System (GMDSS) is extensive and having comprehensive information about the system through publications, manuals and other available means is the only way to improve the operation of the equipment and gain a deeper understanding of its configuration.
It is in the best interest of the vessel to have maximum knowledge of all aspects of the GMDSS system as mandatory training on board and necessary training in emergency situations.
