Shipping was relatively slow in its time to use and implement technological developments. However, this has never been the case when it comes to maritime communications.

From the use of flag signals as the primary means of communication for ships to the advent of the GMDSS system, maritime communications have undergone a long and tortuous evolution over the years.

Maritime communications include interactions between ship and shore, including contact with ports for arrival notices, navigation instructions, and interactions between ships (e.g., navigation safety issues). In today’s age of increased connectivity, shipping legislation is expected to require reporting of information and communication with ships.

Maritime Signal Flags

The use of maritime signal flags has a long history. The system uses a series of flags to spell out a specific message, with each flag representing a specific letter.

Each science has its specific meaning. For example, when a diving support vessel raises flag A, it cannot move from its current position because the divers are underwater. The purpose of this flag is to warn other ships to stay away. Therefore, even without technology, maritime signal flags are considered the most effective means of conveying information.

This basic system of maritime signal flags is also accompanied by associated symbols, known as the International Code of Signals. This is an international system of principles and signals used by ships to communicate critical information, such as information related to navigational safety. This is necessary when there are language difficulties.

Signals are transmitted using radio communications, radiotelegraphs, flag signals, flagpoles, signal lights, or flashing lights. The International Maritime Organization currently maintains the Code, with its most recent printed version published in 2005.

Radiotelegraph

In the early 19th century, Morse code and other similar coded signals made it possible for ships and shores to communicate by radio. Morse code is a method of encoding text characters as a uniform sequence of two signal durations (da and da).

International Morse code encodes the 26 basic Latin letters from A to Z, Arabic numerals, a small set of procedural symbols and punctuation or generation symbols, and a suspended Latin letter É. However, the fact that each letter needed to be sent separately soon made the technology obsolete, as it only added to the expense of shipboard communications.

VHF

The introduction of very high-frequency radio paved the way for a major revolution in maritime communications. This makes communication between ships a reality and improves safety for all involved.

By using FM channels in the VHF or Very High-Frequency radio band, two-way radio transceivers can be used for marine VHF radio on ships, enabling voice communication not only between ships but also between ships and shore with the help of the harbor master.

Marine VHF (VHF) became popular around the world in the early 20th century, soon after Guillermo Marconi invented radio technology. However, with a frequency below 1 GHz, VHF technology is also expected to face some daily challenges related to radio restrictions.

Satellite

To eliminate the challenges of using VHF radio, the International Maritime Organization encouraged all member states to establish a Maritime Mobile Satellite Communications (MMSC) system in 1979. Since the late 20th century, satellite antennas, as the enabler of modern maritime communications, have been the weak link of shore-based systems.

Very Small Aperture Terminal Station (VSATS)

The huge amount of data generated by most satellite communication systems has long posed a serious challenge to maritime communications. This is exactly the problem that small aperture terminals (VSAT) hope to solve.

By subscribing to VSAT services on a monthly basis, operators can make exclusive use of satellite channels to transmit, receive, and avoid data. This enables the network to transmit large amounts of data.

Maritime and Maritime Distress and Safety System

In the early 1990s, maritime communications entered a new era with the introduction of GMDSS (Global Maritime Distress and Safety System). GMDSS is an integrated communication system using radio and ground satellite systems. On February 1, 1999, GMDSS was fully implemented. He officially canceled Morse code as a means of maritime communication.

Under Chapter IV of the International Convention for the Safety of Life at Sea, all cargo and passenger ships over 300 gross tonnage engaged in international voyages are required to carry designated satellite and terrestrial radiocommunication equipment for sending and receiving maritime safety information and distress alerts. This is also mandatory for IMO-based public communications. The Global Maritime Safety System (GMDSS) has also introduced email communications as an option that was previously required for improvement.

In 2022, the International Maritime Organization approved the Global Maritime Distress and Safety System Modernization Plan. The relevant amendments are expected to be implemented in 2024.

Digital Selective Contact

DSC, or Digital Selective Calling, is part of the GMDSS system and enables enhanced communication capabilities. The commands include a remote control to receive and send distress signals, broadcast regular messages, and make emergency safety calls.

As required by the SOLAS protocol, DSC controllers are usually integrated into VHF radios. DSC technology is designed to replace the voice calls used in traditional procedures, transmitting predefined digital messages over VHF.

Automatic Sender Identification System

Under the Basel Convention, the use of ATIS (Automatic Transmitter Identification System) as part of VHF radio is required for inland waterways in Europe. This system transmits the identity of the vessel in the form of a 10-digit code after each voice transmission.

Challenges in Maritime Communications

As modern maritime communications become increasingly digital, this will likely also lead to a large number of network vulnerabilities, requiring satellite communication operators and providers to remain vigilant. This also prompted the International Maritime Organization to recommend in 2017 that ship operators address this issue in their safety management systems.