Telecommunications
GMDSS
by Simon Boyde
When the Titanic sank in 1912 it changed the way that organisations and governments thought about search and rescue at sea. Some 1500 people were killed in the disaster. Fortunately, 700-odd were saved, thanks mainly to the efforts of the Titanic's Radio Officers, who managed to summon help from nearby vessels.
However, the vessel closest to the disaster could not be summoned, as her Radio Officer had just gone off watch after 12 hours on duty. Out of the analysis of this disaster the first SOLAS (Safety of Life at Sea) standards were created which included formal times for radio watch keeping at specific frequencies.
These early standards were based on Morse code of course; voice communications came later, primarily as a result of developments during the Second World War. In the aftermath of the war, the standard spoken vocabulary was developed from British and US Navy practices, which is the origin of the Alpha, Bravo… Zulu letters for spelling words accurately over the radio.
As you can imagine, typing out distress messages using a single key (and, of course, hearing and decoding the same) quite definitely did not help clarity. In the post-war era voice distress messaging formats were standardized in order to assist with summoning help as quickly as possible. It became mandatory for high quality short range communications to be available, together with necessarily lower quality longer range radio systems. We refer to these today as VHF and HF (or SSB) radios.
Major navies round the world switched over to satellite communications in the 1960s, and were closely followed by the merchant marine. An international organization was set up by the members of the International Maritime Organisation (IMO - a sub-body of the United Nations) to manage satellite services for their vessels – this organization, now in private hands, is called Inmarsat. Inmarsat has a special role in maritime communications as the sole provider of satellite based distress signaling.
Roll on to the 1980s and the advent of satellite communications: the original Morse code and parallel voice based communication system was updated to reflect huge changes in technology. The new system (formally adopted in 1979, with mandatory compliance from 1999) is the Global Maritime Distress and Safety System (GMDSS).
There are several differences between the GMDSS systems and what it replaced. Firstly, satellite distress and safety signals became a central part of the process; next: goodbye Morse code.
Clever heads then looked at the costs of running a commercial ship. With 24-hour mandatory radio watch keeping, there was a large cost in keeping trained radio operators on board. It was decided to change the radio watch keeping system: previously either the radio operator in his shack, or a trained officer on the ship’s bridge had to listen to both VHF and HF radios while at sea; this was changed in the 90s so that it was no longer necessary for a physical listening watch to be kept on the radios.
Instead, a messaging facility was added to both VHF and HF radios so that you could call a ship up over the radio in a manner analogous to making a phone call. The radio on the receiving end would signal on its screen and perhaps with an audible signal as well, that an incoming call for that ship needed to be responded to. This facility, also extended to include automated distress messaging, is known as Digital Selective Calling (DSC).
Since 2005, unless an individual flag state has extended previous requirements for ships registered to it, no commercial ship has been required to listen to radios on board – only to DSC alerting.
In the present day, GMDSS equipment encompasses the following:
VHF Radio. All ships need to have at least one permanently installed VHF radio with full DSC support. In addition, they are required to carry at least one handheld VHF radio.
MF/HF Radio. All ships which operate more than 150 miles from land (though properly this should be described in GMDSS sea area A3, which in some countries is right inshore) are required to carry two separate methods of communicating to shore or have one method and the ability to fix the communications device while under way. No one does that, so almost all commercial ships have an Inmarsat C system as well as an HF DSC radio to fulfill this requirement.
Most yachtsmen call an HF radio an SSB radio, though that refers to the method of transmission as opposed to the frequency it transmits at.
Marine Communications Terminology
DSC: Digital Selective Calling. This is a method of calling another ship in a manner similar to making a phone call. You type in the MMSI number of the ship to be called and, as long as they are in range, the phone rings on their bridge. In terms of distress communications, this is a way to transmit a text distress message by radio to other DSC equipped radios and of course shore stations simply by the press of one button.
Navtex/EGC. A way of transmitting weather and other safety information by radio (Navtex) or satellite (when using EGC) to ships at sea. EGC stands for Enhanced Group Call: a satellite message broadcast service.
Inmarsat – the satellite system designated by the IMO to carry this distress and safety information. Distress and safety communications are centred on Inmarsat C, a text messaging service capable of broadcast text messaging via satellite.
Note that this is not a voice telephone system. It is a good idea to have such a system as well. Commercial systems which include voice and support Inmarsat C are readily available but are of course expensive. In the Asian region, good choices for lower cost voice communication are Thuraya (a system which incorporates a mobile phone which snaps into a docking station) and the new Inmarsat Fleetphone. Neither works anywhere near the US and Fleetphone does not like the Eastern half of Australia
AIS – Automatic (ship) Identification System. All commercial vessels transmit a signal at frequent intervals which can be picked up by an AIS receiver and displayed on a screen such that the course and speed of all vessels within range can be easily seen. Yachts can optionally carry a transmitter which will send the same information out to anyone listening. Also broadcast is the ship’s Maritime Mobile System Identity. This looks just like a phone number, and once you know a ship’s MMSI you can call it up on your DSC radio by punching in its number. How do you know a ship’s MMSI? Either they have told you already, or you read it on the screen from its AIS transmissions. Warning: The ISAF website says that an AIS transponder will be mandatory for offshore racing as from January 2010!
EPIRB – Emergency Position Indicating Radio Beacon. Once activated, and when floating in water, it transmits a signal to a satellite giving its position and thereby indicating that a vessel is in distress. This also uses the MMSI number as a unique way of identifying the ship. The ITU has a searchable database of registered EPIRBs.
PLB – Personal Locator Beacon. The same technology as an EPIRB except that they are required to be able to transmit for 24 hours rather than 48 hours duration (ie smaller batteries) and they are not designed to transmit from a floating position, but instead are meant to be hand held. So, the same electronics, but shorter battery life, and therefore small enough to put in a pocket. In most large countries there is a central register as of course these are best registered to an individual. In Hong Kong, like the UK, alas, at the moment we have to register them as secondary EPIRBs to the main EPIRB on board. Please remember though that a PLB is NOT an EPIRB – it will not transmit automatically when immersed in sea water, and cannot be registered as the primary EPIRB for your boat.
SART – Search and Rescue Transponder – designed, when activated, to provide a track back to the unit on a searching vessel’s radar screen. All commercial ships are required to have two or more on board.
GMDSS Equipment for Pleasure Vessels
The equipment list above of course refers to larger commercial vessels. Normal documentation you may read will refer to Convention and non-Convention vessels. The Convention they are talking about is the SOLAS Convention which mandates standards for lifesaving equipment on such ships. Basically, Convention vessels are anything over 300 tonnes or carrying paying passengers, and making an international voyage. A flag state may mandate SOLAS equipment to be on board commercial vessels in local waters as well – and in fact most do, including Hong Kong.
Radio Operators’ Qualifications
A full radio course for a commercial ship is normally at least two weeks long, full time. The reason is of course, is that commercial equipment is intensely complicated. Luckily, for the main equipment on board, there is much simplified equipment available, and therefore the radio course to qualify you to operate it is much shorter – normally around four days long. For VHF radio, the simplified set is Class D DSC; for HF radio, it is Class E DSC.
For non-convention vessels, and non-commercial vessels in shore, what should you have?
Inshore Equipment
VHF radio with DSC Class D – available from GME
EPIRB (yes, that’s right. In Australia, for example, you are required to have one if you go two miles away from land) – also from GME
Navtex – a simple receiver available from Nasa Marine.
AIS – the market leader is Comar
Offshore Equipment
In addition to the Inshore equipment, add:
HF radio with DSC Class E – only one, the ICOM 802E
One PLB for each person on deck at night – again from GME.
Optional but very strongly recommended for Offshore
SART – various suppliers in the commercial field.
Inmarsat C satellite communications system – Thrane and Thrane dominate this market.
Satellite telephone system – for the Asian region, Thuraya (better), Fleetphone (fine – but not Eastern Australia or southern Pacific).
This is a summary of where GMDSS is right now in the commercial field (and believe me, it is a very brief summary) and where we, as non-commercial vessel operators, should be heading to make sure that when it gets tight, we can communicate with those who may rescue us, or perhaps just even turn the wheel so they don’t run us down.
More information on the above products and technologies is available from Storm Force Marine (www.stormforcemarine.com).
Comar AIS Equipment for all AIS gear
Communication Aerials for all antennas
GME Transceivers
Navtex Receiver from Nasa Marine