GMDSS for non-commercial vessels

by Simon Boyde, Technical Director, Storm Force Marine

GMDSS is the Global Maritime Distress and Safety System - a system of terrestrial and satellite communications to enable fast response to Distress situations at sea from shore-based resources.

The basic concept of this new system is that Search and Rescue (SAR) authorities ashore, as well as shipping in the immediate vicinity of the vessel or persons in distress, will be rapidly alerted so that they can assist in a coordinated SAR operation with the minimum of delay.

The new system moves the emphasis from ship-to-ship alerting to ship-to-shore alerting. The GMDSS has introduced technology which has completely transformed maritime communications.

The system also provides for urgency and safety alerting, and also for the broadcast of Maritime Safety Information (weather and navigation reports and warnings).

Rescue in South China SeaWhy is it important to us, non commercial mariners, what the commercial marine boys do? Easy - if we get into difficulty, it is commercial mariners who will come to our rescue, not fellow yachties. And this has been proven in the overwhelming majority of rescues of yachtsmen at sea in the last few years.

It means we need to be able to think the way a professional mariner would, react how they would expect us to react, and communicate with them using the methods they would use for distress and routine communications. There is no point inventing our own little world of yacht to yacht communications which does not permit us to talk to the professional mariners, on ships, who will actually be doing the rescuing.


Commercial operators wanted a way to cut manning levels on ships to save money. Search and Rescue authorities also needed a way to get costs down. So an international system was designed which reduced response times to distress calls, and reduced manning requirements on ships and Marine Rescue Coordination Centres. The IMO, the UN body where mobile marine matters get discussed, calls it the Global Maritime Distress and Safety System - GMDSS.

Essentially, MRCCs needed to cut their expenses down by reducing the time required to rescue people at sea. The best way to do this was to take the 'Search' out of 'Search and Rescue'. Searching take a lot of time!

Ship operators wanted fewer people on board (salaries cost money) so wanted a way to dispense with dedicated radio operators.

The System

What the IMO came up with was a system whereby a requirement for listening watch on distress radio frequencies (listening to the radio) was removed, and instead, in a manner akin to a pager, an alarm rang on the bridge of a ship to tell a watch officer to go to the radio when someone needed to communicate.

They added to that a system whereby, in a distress situation, by simply pressing a prominent (red) button, the ship's position, nature of distress, and identity could be automatically transmitted to shore authorities. Thus was born Digital Selective Calling, or DSC.

In a distress signal, because of how the information is encoded before transmission, there is a much higher quality of transmission. meaning that your position and identity information, extremely important to rescue authorities, has a much higher chance of getting through clearly.

In order to enhance safety at sea the IMO also incorporated text radio broadcasts of navigational warnings, meteorological warnings as well as scheduled weather forecasts for coastal areas into the GMDSS. This system is called NAVTEX.

They coupled this with a high seas system, where similar information, (but with the focus on areas away from coasts), is broadcast to ships at sea by satellite - the Inmarsat Sat C system. As a back up to radio-generated DSC alerts from the ship when in distress, Sat C incorporates distress alerting facilities as well.

Added to all of this were secondary alerting methods (EPIRBs and PLBs, that is, radio beacons) so that if it all went terribly wrong and there was no time to get a radio alert or satellite alert out, the EPIRB (ship) or PLB (personal) beacon could signal to a satellite your distress position. The last part of the jigsaw is enhanced short range locator beacon devices (SARTs) which effectively turn all ship radars into SAR radar devices.

A big complex system it is true. But, it means fast location and detection of distress signals, fast location of distressed vessels, and therefore fast response in an emergency. And it cuts ship operatoring costs down.

The net result however is that no one is listening to voice-over-radio Mayday calls any more. Ships don't have their radios on becasue they are expecting DSC alerts. So if you can't make send a DSC alert, they won't know you are in distres and they won't come to help. You might as well not have a radio at all if it is not DSC capable!

The GMDSS applies to all cargo ships of 300 gross tons or more and to all passenger vessels regardless of size on international voyages
. It became mandatory in 1999. Due to worldwide implementation through regulation, it effectively means that ALL commercial vessels which go offshore have on board:

VHF DSC radio
MF/HF DSC radio
NAVTEX receiver
Inmarsat Sat-C terminal
EPIRB, SART, handheld VHF radios.

All yachtsmen should do the same.

Simon Boyde is a director of Storm Force Marine, regularly races Cave Canem and never ventures offshore without a full set of GMDSS equipment.