The development of maritime communications | Panda Anku

Shipping has traditionally been slow to integrate technological developments, but maritime communications is certainly not a representative case. From flag semaphores as ships’ primary means of communication to the GMDSS, the evolution of maritime communications has been a long one.

SModern communication includes both ship-to-shore interactions, such as voyage instructions, arrival reports, contact with ports, etc., and ship-to-ship interactions, such as navigational safety matters. In an era of increased connectivity, maritime legislation is expected to increasingly mandate ship communications and information reporting (see IMO DCS and EU MRV). But what have been the main means of communication over the years?

Maritime signal flags

This is an ancient system where a series of flags can represent a message, with each flag representing a letter. Individual flags have specific meanings, e.g. B. When diving support vessels hoist the “A” flag, they indicate that they cannot move from their current position because they have a diver underwater and warn other vessels to keep clear. Therefore, maritime signals are the most effective way to send messages without the use of technology.

The main system of flags and associated codes is the International Code of Signals, an international system of signals and codes used by ships to communicate important messages (e.g. relating to the safety of navigation), particularly when language difficulties are encountered. Signals can be sent by flag, signal lamp (“turn signal”), flag semaphore, radiotelegraphy and voice radio. The Code is currently maintained by the IMO, which published a new printed edition in 2005.

The radiotelegraphy

early 19thth In the early 1900s, radio enabled ship-to-shore communication using Morse code or other coded signals. Morse code is a technique that encodes text characters as standardized sequences of two distinct signal durations (dits and dahs). International Morse Code encodes the 26 basic Latin letters (A through Z), one accented Latin letter (É), the Arabic numerals, and a small set of punctuation and procedural marks (prochars). However, the fact that each letter had to be transmitted individually increased the ship’s communication costs and eventually rendered the technology obsolete.


The integration of VHF radio resulted in a drastic transformation of maritime communications, making ship-to-ship communications a reality and improving the safety of all involved. Using VHF channels in the VHF (Very High Frequency) radio band, marine VHF includes two-way radios on ships that provide voice communication not only from ship to ship but also from ship to shore (e.g. harbor masters). The marine VHF has been used around the world since the early 1900s, shortly after Guillermo Marconi invented radio technology. However, it is understood that VHF technology, which provides a frequency of less than 1 GHz, presents several daily challenges related to radio restrictions.

Did you know?

The first significant sea rescue made possible by radio technology took place in 1909 when 1,500 people were rescued from the sinking of the luxury cruise ship RMS Republic. Furthermore, the Titanic tragedy three years later brought the field of marine radio to public attention and marine radio operators were viewed as heroes.

The satellites

To overcome the disadvantages associated with VHF radio, in 1979 the IMO encouraged all member states to deploy Maritime Mobile Satellite Communications Systems (MMSC). As a pioneer of modern ship communication since the end of the 20thth At the beginning of the 20th century, the satellite antenna is a weak link to systems on land.


Ship communications are often challenged by the large amounts of data that most satellite communications systems generate. This is what the VSAT (Very Small Aperture Terminal) is trying to address. By subscribing to VSAT services for a monthly fee, operators can use satellite channels exclusively for sending and receiving voice and data, enabling a network capable of transmitting large amounts of data.


A new era for ship communications began in the early 1990s with the implementation of the Global Maritime Distress and Safety System (GMDSS); an integrated communication system using satellite and terrestrial radio communication systems. Full implementation of GMDSS occurred on February 1, 1999, officially abolishing Morse code as a means of communication at sea.

Under SOLAS Chapter IV, IMO requires all passenger ships and all cargo ships over 300 GT engaged in international voyages to carry certain terrestrial and satellite radiocommunications equipment for sending and receiving distress alerts and maritime safety information, as well as for general communications. The GMDSS offered communication by e-mail as an option that was not previously available.

In early 2022, the IMO approved a modernization plan of the GMDSS with related changes expected to come into force by 2024.

The digital selective call

As part of the GMDSS, Digital Selective Calling (DSC) enabled greater communications capabilities, including remote control commands that could send and receive distress signals, make urgent safety calls, and broadcast routine messages. Nowadays DSC controllers under SOLAS are often integrated into the VHF radio. DSC broadcasts pre-defined digital messages over VHF and is designed to replace the voice calls used in traditional methods.

The automatic transmitter identification system

Under the Basel Accord, European inland waterways require the use of an Automatic Transmitter Identification System (ATIS) as part of the VHF radio, which transmits the vessel’s identity in the form of a 10-digit code after each voice transmission.

Current Challenges

As expected, the increasing digitization of maritime communications has brought corresponding cyber vulnerabilities, requiring constant vigilance from satellite communications providers and operators and prompting the IMO in 2017 to recommend ship operators to address the issue in their SMS.

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