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The Global Maritime Distress and Safety System (GMDSS)
“A ship in the harbor is safe, but that’s not what ships are built for.”
- John A. Shedd
Who comes to mind when we think of modern visionaries that changed the world? Steve Jobs, Elon Musk, or Satoshi Nakamoto? Ever heard of Malcom McLean? He is the man who came up with the idea of the standardized cargo container, revolutionizing how cargo moves to and from ships, trucks, and trains.
As with any revolutionary technology, these changes were not without conflict. The world of dock workers who were previously required to break up cargo, store it and reship it changed overnight. On the upside, it spurred the development of larger and more specialized ocean vessels and opened the floodgate to enormous economic growth in the maritime industry.
Surprisingly though, as the cargo ship grew in size, the technology of containerization also reduced the need for a large ship crew. Satellite comms and innovation in electronics made Morse code radios obsolete, eliminating dedicated radio officers and requiring deck officers to take over communications. But this transfer of radio management tasks to deck officers also increased the risk of missing distress calls from other ships. There was a pressing need to improve the handling of maritime distress calls and search and rescue operations for ships, boats, and aircraft.
That’s what this article is about; the communications technology that keeps these sailors safe at sea.
The Global Maritime Distress and Safety System
The Global Maritime Distress and Safety System (GMDSS) is an international treaty and a set of regulations developed by the International Maritime Organization (IMO) Safety of Life at Sea Convention (SOLAS).
GMDSS gives ship crews a reliable way to receive hazard warnings, make distress calls, and assist in search and rescue operations, no matter where they sail. GMDSS establishes standard procedures, equipment, and protocols that:
Automate ship-to-shore and ship-to-ship communications using both terrestrial radio and satellite-based systems.
Inform vessels of navigation hazards and weather conditions.
Enables distress calls with pertinent location and identification information with the push of a button.
Requires a backup power system to enable emergency communications if primary power fails.
Defines the record-keeping of distress-related communications.
System readiness testing procedure.
The text of the GMDSS regulations for US-based ships can be found in 47 C.F.R. Part 80, Subpart W, and they apply to:
Cargo ships of 300 gross tons and over when traveling on international voyages or in the open sea
Passenger ships carrying more than twelve passengers when traveling on international voyages or in the open sea.
Commercial fishing vessels.
So while this wouldn’t have applied to the S.S. Minow, it certainly would have helped.
While pleasure crafts on open seas have their own set of regulations, this technology is often practical and becoming more affordable.
GDMSS mandates that ships must have the following communications equipment onboard.
Two-way VHF radiotelephone - Cargo ships of 300-500 gross tons require at least two two-way VHF radiotelephones, and all passenger ships and cargo ships of 500 gross tons and above require three.
VHF Digital Selective Calling (DSC) - This digital radio system enables users to initiate calls to specific ships, communicate with ship-to-shore, and share safety and distress information. It transmits the ship ID, location, and time of fix.
NAVTEX receiver - A radio system used to distribute maritime safety information, weather forecasts and warnings, navigational warnings, and search and rescue notices.
Search and rescue transponder (SART) - A self-contained radio communicates a homing signal to either shipboard 9 GHz band RADAR or certain VHF frequencies used by search and rescue aircraft. Cargo ships of 300-500 gross tons require at least one SART, while all passenger ships and cargo ships of 500 gross tons and above require at least two.
Emergency Position Indicating Radio Beacon (EPIRB) - a device that initiates search and rescue operations by transmitting your location using a 406 MHz distress signal to the Cospas-Sarsat satellite system.
Inmarsat / Iridium - If a ship operates outside the coverage of the NAVTEX system, they are required to use a satellite-based system to provide telex, telephone, and data transfer services.
Backup power system - A reserve source(s) of energy to supply radio installations must be provided on every ship for the purposes of conducting distress and safety radio communications in the event of failure of the ship's main emergency sources of power.
Digital Selective Calling
As you can imagine, not having a dedicated radio officer on full-time watch could increase the risk of missing a distress call from other ships. One way to mitigate this problem is with the maritime paging system known as the Digital Selective Calling (DSC) system.
It just occurred to me that thanks to text messaging, there are now multiple generations who don't know what a pager is.
The DSC receiver is programmed to respond to a unique nine-digit Maritime Mobile Service Identity (MMSI) assigned to that ship. The MMSI number is transmitted in a DSC message when a ship or shore station wishes to communicate. A ship's DSC receiver maintains a constant watch on the frequencies assigned to DSC and will alert the crew with an audible alarm for incoming calls to the MMSI.
Depending on what the first few digits of an MMSI are, the number indicates whether it refers to a vessel, group of vessels, shore station, group of shore stations, SAR aircraft, or maritime navigation aid.
This feature allows for simultaneous calling of stations within a group. For instance, 03669999 MMSI can address any US Coast Guard Base station, while 009990000 addresses any VHF coast station.
While at sea, all ships are required to maintain a continuous radio watch for DSC signals at VHF Channel 70 (156.8 MHz) and six other MF/HF marine band frequencies.
The message category: Distress, Urgency, Safety, Routine
The senders MMSI - who sent it.
A code indicating the nature of distress - what’s the problem
The distress coordinates (when connected to GPS) - where are you
Time indication (UTC) - when was this sent
A code indicating the method preferred by the station in distress for follow-up distress communications - how should we reach you
A required feature of DSC radios is the dedicated distress button, which automatically sends a pre-formatted alert to the nearest Coast Guard station and all radio-equipped vessels nearby. Once activated, the DSC will transmit every 3.5 to 4.5 minutes until the message is received or canceled. After sending the message, the radio switches to the corresponding emergency audio band to continue contact with the rescue party.
In addition to distress messages, the DSC system can also be used to initiate routine radio communication between ships and ship-to-shore. In fact, the United States Coast Guard encourages sailors to become familiar with the operation of DSC equipment through this practice.
It’s easy to take modern technologies for granted, we often forget that today’s satellite communication systems were not always ubiquitous. When the SOLAS Convention enacted the GMDSS regulations in 1993, it needed to solve the problem of reliably communicating long distances over open seas. Radio signals over medium and high-frequency bands were the most reliable method of communication at that time. It could be argued that this is still true to some extent.
This spawned the adoption of the NAVTEX (NAVigational TEleX) system. NAVTEX also called narrow-band direct printing (NBDP), is a free global automated service for transmitting navigational and meteorological warnings, forecasts, and urgent maritime safety information to ships at sea. The system, using FSK modulation at a rate of 100 baud, makes it a simple, low-cost, and reliable way to transmit information.
Coast stations transmit NAVTEX messages in English over a frequency of 518 kHz, or 4209.5 kHz for local languages. Time-sharing is used to prevent mutual interference, and the range extends up to 200 nm offshore.
NAVTEX is built on the SITOR (Simplex Teletype Over Radio) protocol. An ingenious system from the 1960s (think Cold War) that uses error correction modes for reliable communication over noisy mediums. To give you an idea of how old NAVTEX technology is, it is based on TELEX, which used teletype machines. TELEX is used to send messages ship-to-ship as well as ship-to-shore.
These days though, the adoption of satellite technology has made SITOR less relevant, to the point where the US Coast Guard has proposed dropping the broadcast of NAVTEX over Medium Frequency (MF) since it is also available on satellite systems.
What about TELEX, is it still used today? You could argue that it is used as part of the cargo transaction process. But the bottom line is that it is still required by International Maritime Organization (IMO) directives for use with Inmarsat as part of the GMDSS station, and you will be tested on it when applying for a GMDSS license.
Search and rescue transponder (SART)
One of the most critical pieces of GMDSS equipment is the Search and Rescue Transponder (SART). SARTs are either fixed permanently into the lifeboat or ship, or they can be carried as a portable device.
Once activated, the SART will listen for and responds to a ship's 9 GHz navigation RADAR with an unmistakable signal that appears as a series of 12 dots on their RADAR screen. The SART will also beep every two seconds when it is detected to let you know help is on the way.
Someone to watch over me
Since the end of the Cold War, international cooperation in maritime rescue missions has significantly improved. The former Soviet Union, the United States, Canada, and France were able to collaborate to create the Cospas-Sarsat system.
Cospas-Sarsat is an array of Low Earth Polar Orbiting (LEO), Medium Earth Orbiting (MEO), and Geostationary Earth Orbiting (GEO) that can detect signals coming from the Earth’s surface transmitted by emergency radio beacons operating at 406 MHz.
The satellites in different orbits can work together:
Low-orbit satellites provide global coverage and Doppler locating capabilities but have an inherent delay due to their orbital characteristics and field of view.
The geostationary satellites offer near-instantaneous detection of 406 MHz distress beacons but do not provide Doppler locating capabilities.
When combined, these satellites offer accuracy of around 3 nm for 406 MHz beacons using Doppler processing. For more modern GPS-capable transmitters, the accuracy significantly improves to within meters.
At mission control centers (MCCs) on the ground, data is received from the various user terminals (LUT) and relayed to the appropriate search and rescue services.
EPIRB and PLB
The Cospas-Sarsat satellites listen for a 406 MHz distress signal from the ground from an Emergency Position Indicating Radio Beacon (EPIRB).
There are different types of EPIRB devices. Some devices are designed to be mounted on a bulkhead and automatically release, float free, and activate when submerged in water. There are also EPIRBs that require manual activation and are typically used in lifeboats. EPIRBs also come equipped with a strobe light.
The EPIRBs are battery-powered, and they should have enough capacity to signal the satellites for at least 48 hours.
The 406 MHz distress signal transmitted by the EPIRBs includes a Unique Identifier Number (UIN) which identifies the ship or user. Registering your UIN in advance helps Search and Rescue teams to access vital information about you and your emergency contacts. ( There is no subscription fee to register a UIN ).
Modern EPIRBs also have a GPS receiver and will also transmit these coordinates Cospas-Sarsat satellites providing accurate location data.
Some Emergency Position Indicating Radio Beacons (EPIRBs) are also equipped with a 121.5 MHz homing signal, an artifact of the aviation Emergency Locator Transmitters (ELTs) system. However, the FAA is attempting to phase them out in favor of the GPS-enhanced 406 MHz Cospas-Sarsat beacons.
The Personal Locator Beacon (PLB) is a smaller version of the EPIRB. They are registered to an individual instead of a vessel. The PLB can be carried by a person or in a ditch bag. PLBs are usually manually triggered, although some are designed to be active when submerged. While some PLBs are also equipped with a strobe light, they are required to function for at least 48 hours.
Similar to the EPIRBs, each PLB has a UIN and should also be registered in advance of use.
PLBs have a place in non-marine applications, and I have carried them for several years on hiking, mountain, and rescue adventures.
I first tried the SPOT gen3 device but switched to the 406 MHz PLB. The frequencies (1610 MHz) that SPOT uses to reach its GlobalStar satellite system require a line-of-sight to the sky and do poorly in forest canopy, mountain terrain, and valleys. SPOT also requires a subscription fee, and the devices are not GMDSS compliant.
GMDSS Satellite Systems
The Cospas-Sarsat is only used to locate EPIRBs and PLBs. A separate satellite system must be used by ships for GMDSS communications. At this time, there are only two certified providers of GMDSS satellite communications service: Inmarsat and Iridium.
The Inmarsat network consists of 14 geostationary satellites with worldwide coverage, with the exception of the Earth's polar regions. The most commonly used shipboard terminals are the Inmarsat-C and Inmarsat-Fleet devices.
Inmarsat-C is a low-speed (600 bps) digital network that supports Telex, Fax, Email, SMS, and data, but not telephone calls. The terminal includes a transceiver unit, display, and omnidirectional non-parabolic antenna that does not require satellite aiming.
Inmarsat-Fleet is a high-end model that uses a directional antenna to track the satellite and GPS assistance for initial aiming. It is a high-speed real-time network that supports voice calls.
Both systems unit has a dedicated distress button and Enhanced Group Call (ECG) function. The distress button can transmit a precoded message in an emergency. ECG on the other hand is used by Inmarsat to selectively address messages to specific groups of ship stations. For example when sending maritime safety information (MSI) to a region.
The other popular network is Iridium. Iridium provides GMDSS service via a constellation of low-earth polar-orbiting satellites covering the entire globe including the polar regions.
Similar to Inmarsat, The Iridium terminal has a dedicated distress button and an Enhanced Group Call (ECG) service for Maritime Safety Information (MSI). But users can also real-time make voice calls through the Iridium satellites
While I have seen Starlink used on some cruising yachts as they are fantastic for use in anchorages with no high-speed cellular data connection. But it is not yet suitable for safety-related purposes mid-ocean, nor is it compliant with GMDSS.
Terra est omnis divisa in partes quadrifariam
One thing to note is that the specific GMDSS communication equipment required depends on a ship's intended operating area and routes. GMDSS divides sea routes into four areas based on practical communication options for each area's distance from a specific type of radio signal.
Sea area A1. An area within the radiotelephone coverage of at least one VHF coast station in which continuous DSC alerting is available.
Sea Area A2. An area, excluding sea area A1, within the radiotelephone coverage of at least one Medium Frequency (MF) coast station in which continuous DSC alerting is available.
Sea Area A3. An area, excluding sea areas A1 and A2, within the coverage of an Inmarsat or Iridium satellite.
Sea Area A4. An area outside sea areas A1, A2, and A3 (generally polar regions). This area is reachable using the Iridium GMDSS terminals.
Ship Security Alert System (SSAS)
There is another safety-related communication system on ships, which while not part of GMDSS, is also required by Safety of Life at Sea (SOLAS chapter XI-2). This is the Ship Security Alert System (SSAS).
SSAS is a joint project between Cospas-Sarsat and the International Maritime Organization (IMO). Think of it as a silent security alarm system that can be activated by the crew in case of a pirate (Maersk Alabama saga) or terrorist attack.
Once activated, rather than sound an alarm on board the ship or alert other ships, it discreetly notifies the ship’s owner or a management third party to dispatch appropriate military or law enforcement to handle the threat.
SSAS-equipped ships must have at least two security alert buttons. One button on the bridge, and the other should be in a prominent position, such as ship the accommodation. All crew members must know the location of the buttons. To prevent false alarms, the activation switch has a protective latch cover. It can also be temporarily locked out during dry dock or layups by the Master or the ship or Ship Security Officer.
GMDSS Crew Requirements
At the start of this article, I mentioned that ships no longer employ dedicated radio officers and instead rely on deck officers to handle communications.
There is a little more to this story. Each officer in charge of a navigational watch and the ship’s master must have a valid GMDSS Radio Operator's License and demonstrate competency in distress, urgency, and safety communications. In a distress situation, one must be available as a dedicated radio operator.
The radio licenses must be posted next to the vessel’s Certificate of Inspection (COI) or Safe Manning Certificate.
The GMDSS Radio Operator's License (DO) is issued by the FCC and requires the applicant to pass both the written FCC Element-1 and the Element-7 exams. The exams are proctored by an FCC-approved COLEM. The FCC does not administer exams.
The Element-1 exam covers basic radio law and operating practices, with a minimum passing score of 18 out of 24 questions. The Element-7 exam covers a wide range of material related to GMDSS radio operating practices, with a minimum passing score of 75 out of 100 questions.
As with all FCC exams, the question pools are published, although each pool must contain at least ten times the number of questions required for a single examination.
Alternatively, applicants may submit proof of passing a certificate issued by the United States Coast Guard or its designee representing a certificate of competency from a Coast Guard-approved training course for a GMDSS endorsement.
Repairing and Inspecting GMDSS equipment
As Captain Ed Murphy has taught us, electronic equipment, especially in marine environments, will fail at the most inconvenient time possible. GMDSS gives you three ways to handle this:
Keep duplicates of certain equipment.
At-sea electronic maintenance.
For some lower-cost gear, it makes more sense to keep a box of extras stowed away and toss the failed unit overboard. But even then, there are going to be times when you need to fix the equipment yourselves. This requires a ship to have someone trained as a qualified radio/electronic officer with a GMDSS Radio Maintainer License.
To qualify as a GMDSS Radio Maintainer, you must pass the FCC Element-1, Element-3 (GROL), and the Element-9 GMDSS Radio Maintenance Practices and Procedures exam. The Element-9 exam covers radio system theory, amplifiers, power sources, troubleshooting, digital theory, and GMDSS equipment and regulations. The last update for the question pool was in September 2012, so there are several questions that do not reflect state-of-the-art technologies. Either way, to pass, you must correctly answer at least 38 out of 50 questions.
Another advantage of obtaining a GMDSS Radio Maintainer is that it allows you to conduct the FCC portion of the compulsory GMDSS inspections on small passenger vessels and larger GMDSS ships.
The GMDSS license exams can be challenging. The good news is you can use the study and testing methods I wrote about in my GROL article to pass the exam. The license, however, is only a starting point; there is no substitute for actual experience with the equipment.
No phone, no lights, no motor car,
not a single luxury
like Robinson Crusoe
it's primitive as can be.