Radio was vital in aiding the rescue of those who survived, and Maritime Radio Day celebrates a global telecoms service based on voice communication and Morse Code.
Its history ranges from its inception on the world’s oceans in 1900 through to the arrival of the advanced Global Maritime Distress Safety System (GMDSS) in 1999, which brought a degree of digital automation to the service.
Marine telecoms services use shortwave radio frequencies, because these signals can bounce between sea level and the ionosphere high above the Earth – which allows modestly powered transmitters to achieve global range.
In recent years, however, the development of satellite phones plus satellite internet VoIP services has added a 21st-century facet to maritime telecoms.
BT’s predecessor, the GPO, were maritime radio pioneers, and set up Portishead Radio in 1928, providing worldwide maritime communications and long-range aeronautical communications right through to 30 April 2000. Until its closure, it was the world’s largest and busiest radiotelephony station, constructed by Marconi and run by the GPO until 1981, when BT took control of the operation.
Portishead Radio played a vital role in preserving North Atlantic maritime shipping from attack during the Second World War, and its operations expanded as the sea lanes grew ever busier in the decades following the war – with its operators handling more than 11 million words of traffic per year by 1974.
Portishead Radio’s decline began in the 1980s, with the rise of satellite services, and after its closure in 2000, the radio station buildings were demolished for a housing development. Alas, not a single plaque commemorates the vital work carried out there.
Marine radio telecoms operate between 156.0 and 174 MHz inclusive, and equipment is installed on all large ships plus most seagoing small craft. It is also used on rivers and lakes. As well as summoning rescue, maritime telecoms is used by vessels to communicate with operators in harbours and locks.
Traditionally, a marine VHF set is a combined transmitter and receiver operating on fixed international frequencies known as channels – the most important being Channel 16 (156.8 MHz), which is the international calling and distress channel.
Most Marine VHF uses what is known as simplex transmission, where communication can only take place in one direction at a time. So, a transmit button is used to determine whether a set is being used to transmit or receive.
Some channels, however, have a duplex capability – where communication can take place in both directions simultaneously when the equipment on both ends allows it.
Modern-day marine VHF radios on seagoing vessels are also required to have some degree of what is called Digital Selective Calling (DSC) capability, which allows a distress signal to be sent with a single button press on a reserved channel (Channel 70) – and also identifies the vessel.
The GMDSS system used today for maritime radio also allows a connection to a GPS receiver, which not only sends a digital distress signal with a single button press but also identifies the vessel’s position.
Vessels at sea also have “phone numbers”, for voice communications, just like landlubbers. Ships from the UK have numbers beginning with the prefixes 232, 233, 234 and 235 – thus, a British ship might have a maritime telecoms number 232003556.
Coastal stations, meanwhile, have the prefix 00 – for example, the Solent Coastguard number for a maritime call is 002320011. Remember that if you find yourself in trouble at sea near the Isle of Wight.
Though it began in 1900, marine radio communications only became relatively widespread on a global scale during the 1930s. At that time, most long-range aircraft had long-wire antennas that would be let out during a call and reeled in afterwards.
Some ships – particularly military vessels – also carry teletypewriters which communicate via shortwave signals in what is known as marine radiotelegraphy. The equipment uses a shortwave radio transceiver with an attachment that generates and receives audio tones, which then drive the teletypewriter.
Maritime radio networks are also used on some land-based telecoms. UK Search and Rescue (UKSAR) teams have access to the simplex (one-way) versions of Channels 24, 62, 63, 64, 85 for operational and training needs, including mountain rescue work in England, Wales and Scotland.
While the “SOS” distress call, created in 1908, remains the most urgent on the high seas, it was not an SOS but the older CQD (often mistakenly thought to mean “Come quick, danger!”) that helped to save 700 lives from the stricken Titanic on that fateful day 105 years ago, which is now Maritime Radio Day.
The BT film archive contains some fascinating insight into the early day-to-day workings of marine telecoms as seen in this 1965 production, Ship to Shore, and 1979’s The Sea Has Many Voices.
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Source: The Telegraph
