The Global Maritime Distress and Safety System
Cover Photo by Matt Hardy
The Global Maritime Distress and Safety System (GMDSS) is an internationally agreed set of safety procedures, equipment, and communication protocols used to increase safety, making it easier to rescue people in distress. There are now two satellite providers of GMDSS: Inmarsat, which is good for equatorial regions, and Iridium, with their 66-satellite constellation in low earth orbit for higher latitudes.
1 / Emergency Position-Indicating Radio Beacons (EPIRBs)
EPIRB’s work by transmitting a coded message on the 406 MHz distress frequency via satellite and earth stations to the nearest rescue coordination centre. There are two types of EPIRB; standard and GPS. Both transmit a signal on 406MHz including an identification code. GPS-enabled-EPIRBs also transmit position information that GEO satellites (Geostationary Orbit) will immediately download to an earth station. The position information may come from a built-in receiver or from a link to the vessel’s own GPS receiver.
Standard EPIRBs’ positions are found using Doppler Frequency Shift Theory by Cospas-Sarsat satellites, requiring two overhead satellite passes before an appropriate position can be found.
It’s important when in distress not to activate all your EPIRBs at once. The larger handheld yacht units built to SOLAS standards should transmit for 48hrs. Once their batteries have died, it’s time to transmit on another unit to ensure the longest period of emergency positioning.
TIP: We recommend the Ocean Signal PLB1 to be installed in life jackets as it has a battery life of 24Hrs minimum.
2 / Digital Selective Calling (DSC)
This is the red button on your VHF/ HF radio. DSC distress alerts, which consist of a preformatted distress message, are used to initiate emergency communications with ships and rescue coordination centres. DSC was intended to eliminate the need for persons on a ship’s bridge or on shore to continuously guard radio receivers on voice radio channels, including VHF channel 16 (156.8 MHz) and 2182 kHz now used for distress, safety and calling.
Modern DSC-equipped MF/HF and VHF radios are connected to a GPS ensuring accurate location information is sent to a rescue coordination centre if a distress alert is transmitted.
TIP: Without a valid MMSI number, depressing your radio’s red button will do nothing! MMSI stands for Maritime Mobile Service Identity. It is a 9 digit unique number that is associated with your specific VHF installation, and really like a digital “Call Sign”.
- Make sure your VHF has DSC capability. If not, invest in a new one.
- Make sure it’s connected to a GPS unit.
- Register and get your individual MMSI number. www.boatus.com/products-and-services/membership/mmsi
- Program your MMSI number into your VHF.
After the setup is complete, depressing your DSC red button on your VHF will send out a general emergency call including details of your MMSI number and your exact position automatically. Even if everyone on board becomes incapacitated, the VHF continues to broadcast the emergency with all relevant details.
A personal MOB AIS /SART (Search and Rescue Transponder) is basically a low power class-A transmitter (1W). Once activated it should start transmitting its position every 1 min and continue until the battery is dead. They also output a new safety-related message (SRM) every four minutes. When held 1m above sea level the AIS/ SART should be received by all AIS receiver units within a 5NM radius.
The best chance of a successful rescue, if you fall overboard, comes from your own vessel. Even in the most moderate of seas, it is alarming how quickly a visual sighting of a man overboard can be lost. A MOB AIS/ SART, once activated, will transmit an alert to all AIS receivers and AIS enabled plotters in the vicinity. The integrated GPS ensures a precise location is sent to your vessel and any others that may be assisting. An additional feature of some units is their ability to activate the DSC alarm on your vessel’s VHF, alerting your crew. Make sure you follow the manufacturer’s instructions when setting up the unit.
SART’s produce a disincentive ‘echo’ on the radar screen of any 9GHz radar. On initial contact with a SART, the radar shows a line of dots giving the range and direction of the casualty. As the radar closes in on the SART the dots broaden into arcs. When the arcs complete one complete circle the SART is within one mile. A search and rescue helicopter at 3000ft can pick up a SART 48 miles away and a radar scanner seven meters above sea level can ‘see’ a SART at about 6 miles.
TIP: The SART starts transmitting when it receives a radar signal. Switch off your vessel’s radar before abandoning ship to prevent your SART from transmitting before rescuers are in range. Position the SART as high as possible to gain the greatest range.
A final reminder is to make sure your personal kit and equipment are regularly tested and maintained. All 406 MHz PLBs/EPIRBs are required to be registered with the local maritime/coastguard agency of your vessel’s flag. According to the MCA, about half of the UK’s population of EPIRBs and PLBs (approximately 40,000) are not registered. This limits the effectiveness of the beacons. Registration is free and can be entered/updated online at www.gov.Uk/406beacon. Remember, if you change your personal details, sell your vessel, or throw away your beacon, contact your local authority.
Batteries need to be tested regularly before use and replaced by the date stamped on the unit.
Air Travel
The lifejacket can be taken on most airlines as cabin/checked luggage but airline ground staff must be notified at check-in. The general rule is one life jacket and two refill canisters per person.
