GMDSS and regulatory communications

25 min read


Overview of GMDSS through to 2021 review changes

Regardless of whether or not a ship makes use of modern communications infrastructure and equipment for commercial and welfare reasons, it is obliged to do so for safety purposes under GMDSS (Global Maritime Distress and Safety System) which began in 1992.

Although it did not entirely replace radio, GMDSS was aimed at putting satellite technology at the heart of the safety communications system for maritime users. The advent of GMDSS saw a major change in the way all maritime communications including commercial messages were handled on ships. It also ensured the demise of the dedicated radio officer.

For over ten years a review of the GMDSS infrastructure and system has been taking place at the IMO. The review is now in its final stages after a working group of the NCSR Sub-Committee completed its deliberations in April 2021.

The changes, which include opening up the GMDSS to satellite service providers other than Inmarsat and removing requirements to carry obsolete systems, will require changes to the Safety of Life at Sea Convention (SOLAS). The decision to allow Iridium to operate as a second GMDSS provider is already incorporated into the rules.

This revision of the relevant regulations in SOLAS chapters II-1, III, IV and V and preparation of related and consequential amendments to other existing instruments will now be submitted to the 104th session of the Maritime Safety Committee (MSC), scheduled to meet in October 2021, with a view to approval and subsequent adoption at MSC 105 in 2022 for their entry into force on 1 January 2024. It is anticipated that all ships communications regulations will be contained in a new dedicated Chapter IV.

Although probably responsible for saving many lives, the maritime communication system that existed prior to GMDSS suffered from a multitude of limitations. GMDSS is an international system that uses land-based and satellite technology and ship-board radio systems to ensure rapid and automated alerting of shore-based communication and rescue authorities, in addition to ships in the immediate vicinity, in the event of a marine distress.

It was adopted by the IMO by way of amendments to SOLAS 1974 Chapter IV in 1988 and entered into force on 1 February 1992 with a phase-in period running until 1 February 1999, depending on ship type and size. With the phase-in period now well past, all ships are now subject to the full GMDSS carriage and maintenance requirements, which vary depending on ship type and area of operation.

The scope of GMDSS and how it operates in practice even in its present form is vast and warrants a complete book in itself in the shape of the IMO-published GMDSS Manual.

Under GMDSS, all oceangoing passenger ships and cargo ships of 300gt and above engaged on all but the shortest of international voyages must be equipped with radio equipment and satellite communications equipment that conforms to international standards.

A survey of GMDSS equipment is needed at regular intervals for the ship to be issued with and retain a valid Safety Radio Certificate. Surveys of radio installation on SOLAS ships should be carried out in accordance with the rules laid down in IMO Res. A.746(18) Survey Guidelines under the harmonised system of survey and certification R 8 (adopted by IMO), and SOLAS 1974 as amended, chapter I, part B.

The radio survey should always be performed by a fully-qualified radio surveyor who has adequate knowledge of the IMO’s relevant conventions and associated performance standards and appropriate ITU Radio Regulations. It is considered very important that the responsible radio operators are properly instructed and trained in how to use the GMDSS radio equipment. The radio licence and certificate for the radio operator/operators should be checked during the survey.

GMDSS operational zones

For the purpose of GMDSS, four operational zones were established, loosely based on distance from shore and in range of different maritime communication systems.

  • Sea Area A1: the area within the radiotelephone coverage of at least one VHF coast station in which continuous DSC (Digital Selective Calling) alerting is available
  • Sea Area A2: the area, excluding Sea Area A1, within the radiotelephone coverage of at least one MF coast station in which continuous DSC alerting is available

  • Sea Area A3: the area, excluding Sea Areas A1 and A2, within the coverage of an approved satellite constellation in which continuous alerting is available; and
  • Sea Area A4: an area outside sea areas A1, A2 and A3.

In practical terms, this means that ships operating exclusively within about 35n-miles from the shore may need to carry only equipment for VHF-DSC communications; those which go beyond this distance, up to about 150 to 400 nautical miles from shore, should carry both VHF-DSC and MF-DSC equipment; while those operating further from the shore but within the footprints of an approved satellite service should additionally carry approved satellite terminal(s). Previously, and until approved Iridium terminals became available in 2021, this has meant that only Inmarsat connected vessels met this requirement.

Sea Area changes post review

As a consequence of the review the sea areas have been redefined as follows;

  • In the updated SOLAS Chapter IV, sea area A3 will be defined as an area, excluding sea areas A1 and A2, within the coverage of a recognised mobile satellite service supported by a shipboard radio station, in which continuous alerting is available.
  • Thus, the sea area A3 will vary depending on the type of mobile satellite service:
  • if Inmarsat is used, the area remains unchanged
  • if Iridium is used, A3 will become global (merging of the areas A3 and A4)
  • if a regional satellite system is used (once approved by MSC), the area A3 will be limited to the coverage zone of this system.

There will be no redefinition of the sea area A4, but it will change for different mobile satellite service providers. That means that the sea area A4 will not exist in the case of a mobile satellite provider such as Iridium with global coverage.

Radio rules in coastal waters

Only ships operating in areas A3 and A4 are obliged to carry satellite communications, which means that radios (operating on VHF, HF and MF) are still considered the primary means of communication in emergency situations. In addition, search and rescue transponders (SARTs) and NAVTEX (Navigational Telex) are also required for GMDSS compliance. However, the latter is now considered as obsolete and the requirement will be removed in the revised chapters of SOLAS.

SARTs are devices that are used to locate survival craft or distressed vessels by creating a series of dots on a rescuing ship’s X-band radar display. The detection range between these devices and ships, dependent upon the height of the ship’s radar mast and the height of the SART, is normally less than about ten miles. Initially only radar SARTS were allowed but since the advent of AIS, a hybrid AIS-SART has been permitted as an alternative.

NAVTEX is an international automated MF direct-printing service for delivery of navigational and meteorological warnings and forecasts, as well as urgent marine safety information to ships. It was developed to provide a low-cost, simple, and automated means of receiving information aboard ships at sea within approximately 200 nautical miles of shore. A NAVTEX is usually in a bracket-mounted cabinet with a small LCD screen displaying broadcast messages with an optional printout.

This equipment is now considered as obsolete and the requirement for it will disappear in the revised SOLAS regulations. Some countries may continue to operate NAVTEX warnings and forecasts, but others are likely to migrate the services to satellite communications.

Inmarsat’s SafetyNET service is an alternative to NAVTEX for ships that are equipped with satellite GMDSS equipment and provides similar information.

GMDSS Satellite service providers

In the early days of GMDSS, Inmarsat C was the preferred option and minimum requirement where satellite services were mandated. The larger Inmarsat A and B systems were also approved but these were quite expensive and considered as ‘overkill’ by many shipowners. In 2018, after more than four years of lobbying, Iridium was finally given the green light as an authorised GMDSS supplier at MSC 99 and ending Inmarsat’s monopoly on safety service provision.

Current compliant Inmarsat services include Inmarsat B, Inmarsat C, Mini C and Fleet Broadband which was approved in 2018 as a replacement for Fleet 77.  

Inmarsat’s L-Band satellite network is available in areas A1 to A3 but does not extend to area A4 which is effectively waters in Polar regions. In these areas HF communications are required although vessels equipped with Iridium communication systems can communicate with shore and ship-to-ship providing both vessels have the equipment.

China’s BeiDou has also applied for recognition as a GMDSS service provider but this has not yet been granted.

Ensuring GMDSS availability (on ship)

GMDSS regulations define three methods of ensuring availability of GMDSS equipment at sea:

  • At-sea electronic maintenance, requiring the carriage of a qualified radio/electronic officer (holding a GMDSS First- or Second-class Radio-Electronics Certificate) and adequate spares and manuals;
  • Duplication of certain equipment; or
  • Shore-based maintenance

Ships engaged on voyages in sea areas A1 and A2 are required to use at least one of the three maintenance methods outlined above, or a combination as may be approved by their administration. Ships engaged on voyages in sea areas A3 and A4 are required to use at least two of the methods outlined above. The lower requirement for A1 and A2 areas recognises that, being closer to shore, ships will have more opportunity to rectify problems.

The vast majority of ships do not opt for at-sea maintenance, preferring instead to duplicate the equipment and use shore-based maintenance (for A3 ships), or use shore-based maintenance only (A1 and A2 ships).

GMDSS equipment is required to be powered from three sources of supply:

  • ship’s normal alternators/generators;
  • ship’s emergency alternator/generator (if fitted); and
  • a dedicated radio battery supply. (The batteries are required to have a capacity to power the equipment for 1 hour on ships with an emergency generator and 6 hours on ships not fitted with an emergency generator).

Other regulatory maritime communications


Automatic Identification System (AIS)

AIS consists of a transponder system in which ships continually transmit data over VHF. The data transmitted is derived from ship’s equipment as regards position, course and speed, from initial input for the ID, which comprises ship’s name and call sign, and from direct manual input for other details such as port of destination and type of cargo.

Updated information is transmitted at regular intervals of very short duration. When received by other ships, the data is decoded and displayed for the officer of the watch, who can view AIS reports from all other AIS-equipped ships within range in graphic and text format. The AIS data may optionally be fed to the ship’s integrated navigation systems and radar plotting systems to provide AIS ‘tags’ for radar targets. It can also be logged to the ship’s Voyage Data Recorder (VDR) for playback and future analysis.

In 2000, IMO adopted a new requirement as part of a revised new SOLAS Chapter V for all ships to carry AIS capable of providing information about the ship to other ships and to coastal authorities automatically. The regulation requires AIS to be fitted aboard all ships of 300gt and upwards engaged on international voyages, cargo ships of 500gt and upwards not engaged on international voyages and all passenger ships irrespective of size. The requirement became effective for all ships by 31 December 2004.

The IMO regulation requires ships fitted with AIS to maintain AIS in operation at all times except where international agreements, rules or standards provide for the protection of navigational information. The regulation requires that the AIS must provide information – including the ship’s identity, type, position, course, speed, navigational status and other safety related information – automatically to appropriately-equipped shore stations, other ships and aircraft and to receive automatically such information from similarly-fitted ships.

AIS transmitters can also be attached to navigational marks or to hazards and transmit information that will complement the sight/ sound signals that may be present. These fixed AIS transmitters can also be used to give other information such as current strength and direction.

Although initially intended only for navigation use by ships and shore authorities, AIS data is now regularly disseminated by commercial operations either to subscribers or on a gratis basis allowing almost anyone to determine any specific ship’s current whereabouts and operational status. The IMO does not condone this use but appears powerless to prevent it.

Because AIS operates on VHF radio, there is a natural limit to the distance over which it can be transmitted. However, there is a number of service providers using satellites that can receive AIS signals when ships are out of the range of shore stations. These services are generally referred to as satellite AIS or S-AIS. Most of the service providers say that their services are targeted purely at national security organisations, but others make no secret of the fact that their customers are often commercial organisations including commodity traders and analysts.

As the IMO further develops the concept of e-navigation, a potential new technology that is sometimes referred to as ‘AIS on steroids’ is being explored: VHF Data Exchange System (VDES). VHF had traditionally been used for voice transmission until the advent of AIS and VDES began as a concept developed by the International Association of Lighthouse Authorities’ (IALA’s) e-NAV Committee. It was originally developed to address emerging indications of overload of the AIS VHF Data Link (VDL) and simultaneously to enable a wider seamless data exchange for the maritime community.

With VDES it will be possible to send broadband data, making it more economical for ships to maintain a data connection at sea by eliminating the need to use satellites in coastal waters, while not compromising on the global connectivity that satellites will be able to provide in the future. VDES is expected to cover up to 50km from the nearest land-based equipment, which will allow ships to benefit from modern communication and navigation methods without increasing costs. VDES is capable of facilitating numerous applications for safety and security of navigation, protection of marine environment, efficiency of shipping and others. Proponents claim it could have a significant beneficial impact on maritime information services including Aids to Navigation and VTS in the future.

Long range identification & tracking (LRIT)

After the use of AIS for reasons of security (rather than its intended aim of an aid to navigation) was found to be inefficient, at MSC 81in 2006 the IMO adopted proposals for long-range tracking and identification (LRIT) of ships, to form part of SOLAS Chapter V.

The obligations of ships to transmit LRIT information and the rights and obligations of SOLAS Contracting Governments and of Search and rescue services to receive LRIT information are established in regulation V/19-1 of SOLAS. Provisions of the amendment came into force in 2009 after which all internationally-trading vessels over 300gt operating outside of GMDSS Sea Areas A1 were required to install the necessary equipment and transmit via satellite technology their identity, location, date and time of position to shoreside bodies authorised to receive it. Ships operating exclusively in coastal Sea Area A1 and fitted with an AIS are exempt.

LRIT requires ships to make regular transmissions of identification and position every six hours to a tracking service which can only release the information with the authority of the vessel’s flag state. Other states with an interest in particular ships may make applications to the flag state for access to the information. If security levels are raised, or if a particular ship becomes of special interest, then the regularity of transmissions and monitoring may be stepped up to as much as once every 15 minutes. The operating standards for LRIT demand that the transmissions can be controlled remotely, without intervention on board. Effectively this means that the transmitter must be of a type that can be polled by a service nominated by the flag state.

For most vessels the Inmarsat C GMDSS system is acceptable, as are some SSAS devices. Some Iridium systems are also approved for LRIT compliance. Whatever equipment is used must either have its own in-built GPS system or be connected to an external GPS.

Ship security alert system (SSAS)

Following the terrorist attacks in New York in September 2001, the IMO Diplomatic Conference on Maritime Security held in London in December 2002 adopted several amendments to SOLAS. These amendments include the introduction of Maritime Security in Chapter XI of SOLAS 74 and incorporated the International Ship and Port Facility Security (ISPS) Code which came into effect on 1 July 2004.

As a consequence, all passenger vessels and other ships over 500gt are required to be provided with a ship security alert system (SSAS). The exact type of equipment that can be used to satisfy the regulation is not specified but some operators have chosen to make use of the GMDSS radio station while many others have installed separate and dedicated satellite equipment. By the standards of modern communications technology, SSAS is quite basic, consisting of a GPS receiver linked to a transmitter, a power supply, some software and activation buttons.

Because the technology is simple and the market huge, a sizeable number of manufacturers have come up with SSAS products. They can all be expected to meet the necessary legal obligations but the ways in which they do this vary somewhat.

The principal differences centre on the methods used to transmit the alarm message, but there are also a number of other features and benefits. As an example, some suppliers will act as a co-ordinating centre and when an alert signal is received, they will contact selected personnel of the owner or manager. At least one has developed an app for smart phones that will give all the information to designated persons whenever an alert is mad

Maritime Single Windows (MSW)

Most ships entering or leaving a port are required to obtain clearance from local authorities. Historically this was done by means of paper documents defined under the FAL Convention submitted by local agents and this is still the case in many ports.

The IMO has attempted to make submission of documents automated and performed electronically in the belief that it is more efficient. A mandatory requirement for national governments to introduce electronic information exchange between ships and ports came into effect from 8 April 2019, under the FAL Convention.

The IMO has encouraged the use of the “single window” concept, to enable all the information required by public authorities in connection with the arrival, stay and departure of ships, persons and cargo, to be submitted via a single portal without duplication. The obligation to create systems for the electronic interchange of information established by Standard 1.3bis does not refer specifically to “single window”, so the Contracting Governments can use systems other than it to comply with this obligation too.  

In June 2021, the FAL Committee issued revised guidelines for setting up a maritime single window that serve as a source of information, advice and guidance for those Member States looking to create a MSW and provides examples of the experience and knowledge gained by some Member States in approaching the implementation of MSW.

As things stand there does not appear to be a universally accepted requirement to use MSWs and very little momentum for their introduction. In most states, port agents are still submitting the data on behalf of ships but there may yet come a time when ships will be submitting the information using their own communication channels.

USCG Notice of Arrival and Departure (NOAD) requirements

After the NY 9/11 terror attacks in 2001, the US authorities became very security conscious. One of the consequences was a requirement by ships to submit information regarding the ship, its crew, cargo and trading history to the US Coast Guard 96 hours before arrival in a US port.

Initially this information could be given by phone, fax or email. Later a dedicated National Vessel Movement Center was established with the possibility to submit the data electronically by way of an e-NOAD.

With many ships’ email systems now being managed by software services, the method of submitting e-NOADs can be effectively managed. The NOAD form is a length and complex document, and the use of software can simplify its completion and transmission. GTMailPlus.eNOAD is GTMaritime’s software solution for the submission of -NOADs.

Performance monitoring

This is an aspect of communications that is likely to come to the fore as the drive to decarbonise shipping accelerates. There are already two regulatory regimes (one operated for ships regardless of flag calling to EU ports or ships flagged in EU countries and another operated by the IMO) that require ships above 5,000gt to monitor, verify and report fuel consumption and CO2 emissions on an annual basis.

There have been arguments made that this information should be sent more frequently – perhaps as part of ships normal noon reporting – so that more transparent data can be obtained by interested bodies.

Currently there is no requirement for this but some ship operators do take performance monitoring seriously and collate data in real time to monitor fleet and individual ship operations for internal purposes.

IMO regulations, with the possible exception of LRIT reporting, have generally not required ships to make regular reports based on the fact that all relevant information should be recorded in logbooks, by data loggers on certain items of machinery or by the ship’s Voyage Data Recorder. 

It is always a possibility that with the trend towards more sophisticated communications equipment being installed on ships then at some future point real time reporting of some aspects of operation may be regulated.