GMDSS, the Global Maritime Distress and Safety System, gets a distress alert ashore without anyone having to hear your voice, and brings safety information to you. On a yacht you meet it as the DSC radio, the EPIRB, the SART and NAVTEX, with AIS working alongside.
What is sea area A1, and what alerts a rescue centre beyond it?
Sea area A1 is the water within range of VHF DSC coast stations, where most coastal cruising takes place. Beyond it your VHF no longer reaches a coast station, but a 406 MHz EPIRB alerts a rescue centre through satellites from anywhere.
Before GMDSS a distress call depended on somebody listening. Its main idea is automatic alerting: a DSC radio or an EPIRB sends who you are and where you are to a rescue centre, even if no one hears a voice call.
What reaches the shore depends on where you sail. Sea area A1 is the water within range of VHF DSC coast stations, where most coastal cruising takes place. Further out, your VHF no longer reaches a coast station. A 406 MHz EPIRB, working through satellites, still alerts a rescue centre from anywhere.
| Sea area | Defined by |
|---|---|
| A1 | Range of VHF DSC coast stations |
| A2 | Range of MF DSC coast stations |
| A3 | Satellite communication coverage |
| A4 | Everything beyond, mainly the polar regions |
How does an EPIRB tell rescuers where I am?
An EPIRB transmits a coded 406 MHz alert that Cospas-Sarsat satellites pass to a rescue centre, with its own position if it has built-in GPS. A weak 121.5 MHz signal lets a lifeboat or helicopter home in.
An EPIRB is the yacht's emergency beacon. Switched on, it transmits on 406 MHz a coded alert that the Cospas-Sarsat satellites pick up and pass to a rescue centre. A beacon with built-in GPS sends its own position in the alert, so rescuers get it faster and more precisely; without GPS the satellites have to work the position out.
The beacon also sends a weak 121.5 MHz signal, which a lifeboat or helicopter homes in on for the final approach.
A Category I EPIRB sits in a bracket with a hydrostatic release: if the yacht sinks, it floats free and switches itself on. A PLB alerts through the same satellites, but it is worn by a person and registered to that person; the EPIRB is registered to the boat.
How do I test my EPIRB without sending a false alert?
Use only the built-in self-test, as the maker's manual says: switching the beacon on sends a live alert. If it does go off by mistake, switch it off and tell the coastguard or MRCC at once.
| Job | How |
|---|---|
| Registration | Keep your details and the boat's up to date: rescuers use them to phone the owner and identify the yacht. A used boat's beacon must be re-registered to you |
| Testing | Only the built-in self-test, as the maker's manual says. Switching the beacon on sends a live alert |
| False alert | Switch it off and tell the coastguard or MRCC at once: the alert may already be in the system |
What does a SART look like on a ship's radar screen?
A SART paints a line of 12 dots on a ship's 9 GHz (X-band) radar. The SART is at the dot nearest the ship; the line runs on beyond it.
A SART goes with you into the liferaft. It answers a ship's 9 GHz (X-band) radar and paints a line of 12 dots on her screen. The SART is at the dot nearest the ship; the line runs on beyond it. Its range depends on height, so mount it on its pole or hold it as high as you can.
An AIS-SART does the same job another way: it transmits AIS messages with its own position and shows on any AIS display nearby, with no radar needed.
Can I rely on AIS instead of keeping a lookout?
No: AIS is an aid, not a lookout. Many boats carry no AIS and a set can be switched off, so an empty screen does not mean an empty sea. Keep a proper lookout whatever the plotter shows.
AIS sets broadcast a vessel's identity, position, course and speed on VHF, and plotters show them as targets. Ships carry Class A. Yachts usually fit Class B, a simpler small-craft set that transmits at lower power and reports less often.
An empty AIS screen does not mean an empty sea. Many boats carry no AIS, and a set can be switched off. Keep a proper lookout whatever the plotter shows.
Questions from this topic, as the app asks them. Open one to see the answer.
Which GMDSS sea area are you sailing in?
B. A1
Sea area A1 is defined by the range of VHF DSC coast stations.
You are buying an EPIRB for the boat. Why choose B?
C. Its position reaches rescuers faster and more precisely
A GPS EPIRB sends its own position in the alert; without GPS the satellites must work it out.
What happens to this beacon if the yacht sinks before anyone can reach it?
A. It floats free and switches itself on
Category I: the hydrostatic release frees it at depth; it floats up and activates automatically.
The rescue ship's radar shows this. Where exactly is the SART?
B. At the dot nearest the ship
The SART is at the first dot, the one closest to the ship; the line runs on beyond it.
Your NAVTEX prints this header. What does the letter B tell you about the message?
A. It is a meteorological warning
The second letter is the subject: A navigational warning, B meteorological warning, D SAR, E forecast.
Does this mean the way ahead is clear of other vessels?
D. No — many boats have no AIS; keep a lookout
AIS is an aid, not a lookout: many craft carry none or have it switched off.
All 20 questions of this topic are in the app: practice by topic with the reason after every answer, your mistakes brought back, and a timed mock exam. Free, no sign-up, in the browser or in Telegram.