Prerequisites
To sit the Yachtmaster Offshore exam you must hold a GMDSS-compliant marine radio operator's certificate, normally the RYA/Ofcom Short Range Certificate (SRC), or a higher one such as the Long Range Certificate (LRC) or a GOC. This lesson assumes you have passed the SRC and know how to operate a VHF DSC set: selecting channels, making routine calls, using the MMSI, and the phonetic alphabet. Your yacht should also hold a Ship Radio Licence from Ofcom, which issues the vessel's MMSI and call sign. The lesson builds on that knowledge to the depth an offshore skipper needs: sea areas and equipment beyond VHF, distress procedures under pressure, relay and cancellation, and beacon management.
Learning Objectives
By the end of this lesson you should be able to:
- Describe the purpose and structure of GMDSS, and define sea areas A1 to A4.
- Explain the equipment carried for each sea area and what a well-equipped offshore yacht should carry.
- Send a DSC distress alert and a correct voice Mayday, Pan-Pan and Securite.
- Respond correctly to a distress alert received from another vessel, including Mayday Relay.
- Cancel a false distress alert.
- Explain MF/HF DSC, Inmarsat C, SafetyNET and NAVTEX, and use them to receive Maritime Safety Information.
- Register, test, maintain and activate a 406 MHz EPIRB, and understand PLBs, SARTs and AIS-SARTs.
- Keep a radio log, observe the correct watchkeeping and licensing requirements, and brief the crew so that anyone can raise an alert.
RYA syllabus mapping. This lesson covers the Yachtmaster Offshore course objectives for GMDSS operations: operate VHF DSC and MF DSC equipment correctly for all priority levels (Mayday, Pan-Pan, Securite, routine); execute distress, urgency, safety and routine call protocols without hesitation; manage EPIRB, SART and NAVTEX equipment including testing and maintenance; and handle false alert cancellation and relay procedures. It also supports the entry requirement for a GMDSS-compliant certificate (SRC minimum), and the safety awareness and signals part of the practical exam.
Exam note. The examiner may hand you a scenario ("your crewman has gone over the side, show me what you would do on the radio") and expect you to operate the set correctly and send a complete message with the right wording and no hesitation. A laminated MIPDANIO card at the set is allowed and sensible.
What GMDSS Is and Why It Exists
Before 1999, rescue depended on ships keeping a listening watch on 500 kHz Morse and 2182 kHz voice. If the crew was overwhelmed before they could send a message, or no one heard it, nobody came. The Global Maritime Distress and Safety System, adopted by IMO into SOLAS and fully implemented in 1999, replaced listening with automation. Its functions are:
- Alerting (ship to shore, ship to ship and shore to ship)
- Search and rescue coordination communications
- On-scene communications
- Locating signals (homing)
- Promulgation of Maritime Safety Information (MSI)
- General radiocommunications
- Bridge-to-bridge communications
GMDSS is mandatory for SOLAS vessels (cargo ships of 300 gross tonnage and over, and passenger ships). Pleasure yachts are not obliged to carry the full GMDSS fit, but commercially coded yachts must carry equipment set by the MCA codes for their category, and every offshore skipper uses the same system: the coastguard listens for DSC on Ch 70, rescue centres receive EPIRB alerts, and MSI arrives by NAVTEX and SafetyNET.
Sea Areas
GMDSS divides the oceans into four sea areas based on the range of the shore-based facilities.
| Sea area | Definition | Typical range | Primary equipment |
|---|---|---|---|
| A1 | Within radiotelephone coverage of at least one VHF coast station with continuous DSC alerting | 20 to 30 miles offshore | VHF DSC |
| A2 | Excluding A1, within coverage of at least one MF coast station with continuous DSC | About 100 to 150 miles | MF DSC |
| A3 | Excluding A1 and A2, within coverage of a recognised mobile satellite service (Inmarsat geostationary, roughly 70 degrees N to 70 degrees S; Iridium) | Ocean basins | Inmarsat C or Iridium GMDSS, or HF DSC |
| A4 | Outside A1, A2 and A3 | Polar regions | HF DSC (or Iridium) |
The diagram below shows the relationship between A1 and A2 around a coast station.
Typical ranges are guidance only. VHF range is roughly 2.2 times the square root of the antenna height in metres for each station, plus the same for the other: a yacht with a masthead antenna at 15 m and a coast station antenna at 100 m gives about 2.2 x (3.9 + 10) = 31 nautical miles, but a handheld set held at 2 m reaching a small craft gives only about 2.2 x (1.4 + 1.4) = 6 miles. Always judge your own range from the antenna heights, and always assume that your signal will not be heard beyond the horizon.
Around the UK, HM Coastguard covers almost the whole coastline to A1 standard. Note that some countries never declared A2 areas, and the UK withdrew its MF DSC watch in some regions; always check the current Admiralty List of Radio Signals (ALRS) Volume 5 (GMDSS) for the area you are sailing in. A typical Yachtmaster Offshore passage, for example Falmouth to Crosshaven or across the Bay of Biscay, will take you well outside VHF range, so you must plan for what you will rely on there: EPIRB, satellite communications and, if fitted, SSB/HF.
Equipment Carriage
For SOLAS ships the carriage requirements grow with the sea area:
For an offshore yacht going beyond A1, a sensible fit is:
- Fixed VHF DSC (Class D) connected to GPS, with a masthead antenna, plus an emergency antenna in case the mast is lost.
- Waterproof handheld VHF, ideally with DSC and GPS, kept in the grab bag.
- 406 MHz EPIRB with GPS, registered, in a float-free bracket with hydrostatic release.
- Personal Locator Beacons (PLBs) and/or AIS MOB beacons on lifejackets.
- SART or AIS-SART for the liferaft.
- NAVTEX receiver.
- A satellite communications device (Iridium handset or terminal, Inmarsat C, or a messenger service) for weather, medical advice and routine traffic when out of VHF range.
- AIS transponder (Class B at least).
Image: Billlion, CC BY-SA 3.0, via Wikimedia Commons
Priority of Communications
Every radio message has one of four priority levels, in this order:
| Priority | Voice prefix | Use | Example |
|---|---|---|---|
| Distress | MAYDAY | A vessel, aircraft or person is threatened by grave and imminent danger and requires immediate assistance | Sinking, fire out of control, person overboard not recovered, life-threatening medical emergency |
| Urgency | PAN-PAN | A very urgent message about the safety of a vessel or person, where danger is not imminent | Dismasted with no engine drifting slowly towards a lee shore 10 miles off; seriously ill crew needing medical advice (Pan-Pan medico) |
| Safety | SECURITE | Important navigational or meteorological warning | A floating container, a gale warning, a buoy off station |
| Routine | none | Everything else | Marina calls, link calls |
Ch 16 (156.8 MHz) is the VHF voice distress, urgency and safety channel; Ch 70 is reserved exclusively for DSC. You must never use voice on Ch 70.
Sending a Distress Alert by VHF DSC
DSC turns a long, error-prone voice message into a short digital burst that every DSC set in range receives with an alarm, and which carries your MMSI and position automatically. The correct order is DSC alert first, then voice Mayday.
Procedure
- Check that the radio has a valid GPS position. If not, enter position and time manually if time allows.
- Lift the cover of the red DISTRESS button. If time permits, select the nature of distress from the menu (fire, flooding, collision, grounding, listing, sinking, disabled and adrift, abandoning ship, piracy, man overboard, undesignated).
- Press and hold the distress button for about 5 seconds until the alert is sent.
- The set automatically returns to Ch 16. It will repeat the alert every few minutes until an acknowledgement is received.
- Wait about 15 seconds for an acknowledgement from a coast station, then send the voice Mayday on Ch 16 whether or not acknowledged. Do not wait indefinitely.
- Listen for a reply; if none, repeat the voice Mayday.
If the alert is acknowledged by DSC, the set stops repeating. The coastguard will then reply by voice on Ch 16.
The voice Mayday: MIPDANIO
The voice message must follow a fixed format so that the listener knows where each piece of information will come.
A complete example:
MAYDAY MAYDAY MAYDAY. THIS IS yacht Blue Heron Blue Heron Blue Heron, call sign MABC7, MMSI 235 123 456. MAYDAY Blue Heron, call sign MABC7, MMSI 235 123 456. My position is 49 degrees 42 minutes North, 006 degrees 15 minutes West. I am holed and sinking. I require immediate assistance. Four persons on board. Abandoning to liferaft, red hull, EPIRB activated. OVER.
Points to note:
- The identity appears twice: three times at the start (after "This is") and once more in the "Mayday" line.
- Position as latitude and longitude, or as a bearing and distance from a charted point ("170 degrees from Lizard Point, 12 miles"). Speak it slowly.
- Nature of distress in plain words.
- Information: anything that helps the rescuers find and help you: intention to abandon, liferaft and hull colour, EPIRB and SART activated, injuries.
- Keep a written card by the radio so that any crew member can send it.
Controlling traffic during distress
The station controlling distress traffic (normally the coastguard, or the casualty) may impose radio silence with "SEELONCE MAYDAY". Others must not transmit on that channel. "SEELONCE FEENEE" means distress traffic has ended and normal working may resume. "PRUDONCE" means restricted working may resume. A station other than the controller may use "SEELONCE DISTRESS" to quieten interference.
Direction finding
Lifeboats and some SAR aircraft carry VHF direction finders and may ask you to transmit for a bearing: "Mayday, yacht Blue Heron, this is Falmouth Lifeboat, for direction finding purposes request you hold your press to transmit button closed for ten seconds followed by your name, repeat three times on this frequency, over." Reply "Mayday, Falmouth Lifeboat, this is Blue Heron," transmit for ten seconds, say the boat's name, and repeat the sequence three times. The request may be repeated as the rescue craft closes. Several Coastguard stations can also take a DF bearing on a Channel 16 transmission.
Pan-Pan and Securite
A Pan-Pan is preceded by a DSC urgency alert (all ships or to a specific station), then a voice call on Ch 16:
PAN-PAN PAN-PAN PAN-PAN. ALL STATIONS ALL STATIONS ALL STATIONS. THIS IS yacht Blue Heron Blue Heron Blue Heron, call sign MABC7, MMSI 235 123 456. My position is 50 degrees 05 minutes North, 004 degrees 52 minutes West. I have lost my rudder and am drifting south-east at 2 knots. I require a tow. Three persons on board. OVER.
A Securite call is normally announced on Ch 16 (and by a DSC safety alert), with the message itself sent on a working channel:
SECURITE SECURITE SECURITE. ALL STATIONS ALL STATIONS ALL STATIONS. THIS IS yacht Blue Heron. For navigational warning listen on channel 67. OUT.
MF/HF DSC
Beyond VHF range, the same DSC principles work on medium and high frequencies.
| Band | DSC distress frequency | Voice distress frequency | Range |
|---|---|---|---|
| MF | 2187.5 kHz | 2182 kHz | About 150 miles (groundwave) |
| HF 4 MHz | 4207.5 kHz | 4125 kHz | Long range by skywave, varies with time of day |
| HF 6, 8, 12, 16 MHz | 6312, 8414.5, 12577, 16804.5 kHz | 6215, 8291, 12290, 16420 kHz | Global, depending on propagation |
The higher HF bands work better by day and over longer distances; the lower bands by night and over shorter distances. A long-range MF/HF set requires the LRC. Many yachts fit an SSB receiver for weather and HF email, but transmitting requires the right licence and certificate.
Satellite Systems: Inmarsat C and SafetyNET
Inmarsat C is a text-only, store-and-forward satellite terminal using an omnidirectional antenna, so no pointing is needed. It sends and receives messages and includes a distress button that sends an alert with MMSI, position and nature of distress to a Rescue Coordination Centre.
Its Enhanced Group Call (EGC) receiver picks up SafetyNET, the satellite equivalent of NAVTEX, which broadcasts MSI to defined NAVAREAs and METAREAs, coastal areas, or circular areas around an incident.
Since 2020 Iridium has also been recognised as a GMDSS satellite provider, and its "SafetyCast" service carries MSI. For most yachts, an Iridium handset with an SOS button, or a satellite messenger, is the realistic long-range alerting backup after the EPIRB, though messenger devices are not part of GMDSS and route their alerts via commercial emergency centres, adding delay.
NAVTEX
NAVTEX is an automated, printing or screen receiver for MSI in coastal waters, out to about 300 to 400 miles from the transmitter.
Image: K. Krallis, SV1XV, CC BY-SA 3.0, via Wikimedia Commons
- 518 kHz carries the international service in English.
- 490 kHz carries national services, often in the local language (the UK uses it for inshore waters forecasts).
- Each station has a letter and transmits in a fixed time slot every 4 hours, which avoids interference between stations.
Each message begins with a four-character identifier, for example EA47:
| Character | Meaning | Example |
|---|---|---|
| 1st | Transmitting station | E = Niton |
| 2nd | Subject indicator | A = navigational warning |
| 3rd and 4th | Serial number | 47 |
Common subject indicators: A navigational warnings, B meteorological warnings (gales), C ice reports, D search and rescue information and piracy, E weather forecasts, F pilot service messages, G AIS messages, J GNSS messages, K other electronic navaid messages, L additional navigational warnings, Z no messages on hand. Subject indicators A, B, D (and normally L) cannot be deselected by the user, because they are essential to safety. The receiver will not print a message it has already received correctly, using the serial number.
Before an offshore passage, set the receiver to the stations along the route and to the subjects you need (A, B, D, E and L at least), and check for gale warnings and navigational warnings the night before departure.
EPIRBs, PLBs and SARTs
406 MHz EPIRBs
An Emergency Position Indicating Radio Beacon transmits on 406 MHz to the Cospas-Sarsat satellites. The modern MEOSAR constellation (on Galileo, GPS and GLONASS satellites) detects and locates an alert within minutes almost anywhere in the world. A GPS-equipped beacon includes its position in the burst, typically to within 100 m; without GPS the satellites calculate position by Doppler, to within a few miles and with delay. The beacon also transmits a low-power 121.5 MHz homing signal (and on newer models AIS) so that rescue aircraft and lifeboats can home onto it. A Category I EPIRB is float-free with a hydrostatic release unit (HRU) and activates automatically when it floats; Category II is manual.
The alert flows from the satellite to a ground station (LUT), to a Mission Control Centre (in the UK, the UK MCC at the Aeronautical Rescue Coordination Centre), then to the responsible MRCC. The coastguard looks up the beacon's 15-character hex ID in the registration database to find your vessel, emergency contacts and passage details, and starts calling the boat and the contacts.
Registration. In the UK, register free with the UK Beacon Registry (run by the MCA). The registration is linked to the vessel and her MMSI, and the hex ID is coded for the flag state. Update the registry if you sell the boat, change the name, change emergency contacts or move the beacon to another vessel. An unregistered beacon still works, but rescuers lose valuable time identifying you. Before each long passage, update your emergency contact with your passage plan.
Testing and maintenance.
- Carry out the self-test monthly following the manufacturer's instructions. The self-test checks the circuitry without sending a live alert. Never test by activating it.
- Check the battery expiry date (typically 5 to 10 years) and the HRU expiry date (usually 2 years), and service as specified.
- Check the bracket, lanyard and that the beacon is not obstructed in its float-free position.
Activation. In grave and imminent danger, activate the EPIRB and keep it with you. If you abandon ship, take it into the liferaft and tie it on outside by its lanyard, floating, with a clear view of the sky. Do not switch it off until rescued, unless told to by the rescue authorities.
Image: Addshore, CC BY-SA 3.0, via Wikimedia Commons
Personal Locator Beacons are smaller 406 MHz beacons registered to a person rather than a vessel. They are excellent on a lifejacket offshore, but most must be held out of the water with the antenna vertical, and most have shorter battery life (minimum 24 hours).
SART and AIS-SART
A radar SART (9 GHz) responds when hit by an X-band radar, producing a line of 12 dots outward from its position on the searching vessel's display. As the searching vessel gets closer, the dots become arcs and then complete circles around the SART's position.
Image: National Imagery and Mapping Agency, public domain, via Wikimedia Commons
Image: Ulflarsen, CC BY-SA 3.0, via Wikimedia Commons
The SART must be switched on in the liferaft and raised on its pole at least 1 m above sea level (higher if possible), because the range depends on its height: about 5 miles to a ship's radar and about 30 miles to an aircraft's. A SART listens for a radar pulse and it only starts to respond when it detects one, so it will not respond if there is no X-band radar in range. An AIS-SART transmits its GPS position as an AIS target, displayed on chart plotters and ship AIS within about 5 miles at sea level. AIS MOB beacons on lifejackets work the same way and can also trigger a DSC alert to the mother vessel.
Radio Licensing, MMSI and the Radio Log
- Three requirements. Equipment must be type approved (conformity marked; sets bought abroad may lack the international channels and can be confiscated), licensed, and operated by or under the supervision of a certificate holder.
- Ship Radio Licence. Every vessel that carries VHF, DSC, EPIRB, AIS or other radio transmitters needs an Ofcom Ship Radio Licence (free online, revalidated every ten years and amended when equipment changes; carried on board, since foreign inspections are stricter than UK ones). It records the call sign, which stays with the vessel through changes of ownership, the MMSI and the equipment on board. A handheld VHF used on a vessel normally needs to be listed on the licence, or covered by a Ship Portable Radio Licence if it is used on several vessels.
- MMSI. A nine-digit Maritime Mobile Service Identity, beginning with the Maritime Identification Digits of the flag state (232 to 235 for the UK). Your DSC set transmits it in every call. Enter it correctly, and have the radio programmed with it before leaving the dock: a set with no MMSI cannot send a DSC alert. A handheld DSC set needs its own MMSI.
- Operator certificate. The person using the set must hold the SRC or higher (the Long Range Certificate for MF, HF and satellite equipment), or be operating under the supervision of a certificate holder, as the licence requires. The SRC has two parts, the Certificate of Competence and the Authority to Operate, which is issued from age 16. The skipper is responsible for having someone competent aboard, and a distress alert is sent on the skipper's authority.
- Radio log. Record the date and time (UTC), the stations called, any distress, urgency or safety traffic and routine tests of the equipment. Alerts sent in error must be logged. The log is also evidence in any investigation.
- Testing. Do not test the distress function. Test DSC by an individual call to another vessel or a test call to a coast station. Test the handheld and the main radio on a radio check with the Coastguard, who will normally reply on Ch 16 or a working channel. If asked to change channel, reply on the stated channel.
- Watchkeeping at sea. Keep a continuous listening watch on Ch 16 and DSC Ch 70 at sea (the DSC receiver on Ch 70 is a requirement of the Radio Regulations on any vessel fitted with DSC). Do not switch the radio off in harbour if you are leaving within hours.
Maritime Safety Information You Receive Underway
MSI reaches a yacht by several routes, and an offshore skipper should have at least two.
| Source | Where | Notes |
|---|---|---|
| NAVTEX | 518 kHz, to about 300 to 400 miles | Automatic; set to the stations on your route |
| Coastguard VHF broadcasts | Announced on Ch 16, then a working channel (Ch 67 for small craft in the UK) | Gale warnings, inshore waters forecast, shipping forecast times announced by the coastguard |
| SafetyNET (Inmarsat C EGC) | Whole ocean areas (NAVAREAs and METAREAs) | Needs an Inmarsat C or an EGC receiver |
| Iridium SafetyCast | Global | Needs Iridium terminal |
| Weather fax, HF email, GRIB files | Via SSB or satellite | Used for routing; not GMDSS |
NAVAREA I covers the UK and North-East Atlantic. Gale warnings and forecasts for METAREA I are broadcast by NAVTEX and SafetyNET. Record warnings that affect your route in the log and plot dangerous areas on the chart.
Receiving a Distress Alert and Mayday Relay
If your DSC set alarms with a distress alert, record the details (MMSI, position, nature, time) and listen on Ch 16. In sea area A1, a coast station should acknowledge within a short time.
- Do not acknowledge by DSC. Under current IMO guidance, ships should only acknowledge a DSC distress alert by DSC if directed by a coast station or RCC. Unnecessary DSC acknowledgements stop the casualty's set from repeating and can cause confusion. Wait about five minutes for a coast station to acknowledge. If none has, and you can help, acknowledge by voice on Ch 16 (on MF/HF, the ITU procedure is DSC acknowledgement).
- If you hear the voice Mayday and you are able to help, and the coast station has not acknowledged, acknowledge by voice on Ch 16: "MAYDAY Blue Heron, Blue Heron, Blue Heron, THIS IS Sea Swallow Sea Swallow Sea Swallow, RECEIVED MAYDAY." Then give your position, speed and estimated time to reach the casualty.
- Inform the coastguard by any means.
Mayday Relay is sent when a vessel in distress cannot transmit herself, or when you have heard a Mayday that has not been acknowledged and you cannot help directly, or when you consider further help is needed.
MAYDAY RELAY MAYDAY RELAY MAYDAY RELAY. ALL STATIONS ALL STATIONS ALL STATIONS (or Falmouth Coastguard x3). THIS IS Sea Swallow Sea Swallow Sea Swallow, call sign 2ABC4, MMSI 235 987 654. Following received from yacht Blue Heron, MMSI 235 123 456, at 1432 UTC. MAYDAY Blue Heron, position 49 42 North 006 15 West, holed and sinking, four persons on board, abandoning to liferaft. OVER.
You may also relay by DSC, addressed to the coast station (individual call), using the distress relay format. Do not send a DSC "all ships" relay in A1 when a coast station is within range.
Duty to assist
Under SOLAS Chapter V Regulation 33, the master of a vessel at sea that is able to provide assistance, on receiving information that persons are in distress, is bound to proceed with all speed to their assistance. If you are unable to, or it would be unreasonable or unnecessary, you must record the reason in the log and inform the SAR authority. UK law makes failure to assist an offence.
False Alerts
Thousands of false DSC and EPIRB alerts occur each year, wasting SAR resources and sometimes masking genuine emergencies. A false alert is not an offence if it is cancelled promptly; failing to cancel it can be.
To cancel an inadvertent VHF DSC distress alert:
- Switch off the transmitter immediately if the alert is still repeating, or use the set's cancel function if it has one (some sets can send a DSC distress cancel, many cannot, and the voice cancellation is always needed).
- Switch on again and set to Ch 16.
- Broadcast: "ALL STATIONS ALL STATIONS ALL STATIONS. THIS IS Blue Heron Blue Heron Blue Heron, call sign MABC7, MMSI 235 123 456, position 50 08 North 005 03 West. CANCEL my distress alert of 1215 UTC. Blue Heron. OUT."
- Note it in the radio log.
For an inadvertent EPIRB activation, do not switch the beacon off first. Contact the nearest coastguard by any means (VHF DSC urgency call, phone, satellite phone), give your position and the beacon's hex ID, and switch it off only when the rescue centre tells you to. The satellites will already have passed the alert on, and a beacon that goes silent before the RCC knows it was a mistake can keep a search going for hours. A SART switched on by accident is switched off and reported, in case a passing ship has seen the echo and started a search.
Common Mistakes
The diagram summarises the most common errors examiners and coastguards see.
- Voice Mayday without a DSC alert. The DSC alert sounds an alarm on every set in range and gives an exact position; do it first.
- Waiting for acknowledgement before speaking. Send the voice Mayday about 15 seconds after the DSC alert regardless.
- Missing elements in the Mayday, especially position. Keep a MIPDANIO card by the radio.
- Not cancelling a false alert, or switching off a beacon without telling anyone.
- Using Mayday when Pan-Pan is appropriate (or vice versa). Dismasted in open water with an engine is not Mayday; drifting onto rocks is.
- Acknowledging a DSC distress alert by DSC when a coast station is in range.
- Unregistered or out-of-date EPIRB, expired battery or HRU.
- No MMSI programmed, or the wrong MMSI, so DSC calls and alerts fail or identify the wrong vessel.
- Radio not connected to GPS, so the alert carries no position.
- Not keeping watch on Ch 16 and DSC Ch 70 at sea.
- Forgetting that VHF range is line of sight. A handheld with its antenna 1.5 m above the sea may reach only a few miles to another small craft.
Worked Scenario: Fire 60 Miles South-West of Scilly
At 0310 a fire breaks out in the engine compartment of your 11 m yacht, 60 miles south-west of the Isles of Scilly, outside VHF coast station range (sea area A2/A3 depending on charts). Extinguishers have failed and smoke is filling the saloon. Four crew.
- Alert. Send a VHF DSC distress alert with nature "fire". It may be heard by a ship in range even though no coast station will hear it. Follow with a voice Mayday on Ch 16.
- Activate the EPIRB. This is the alert that will reach the MRCC. With a GPS beacon, Falmouth Coastguard will have your position within minutes, call your registered emergency contact and broadcast a Mayday Relay by satellite and MF to ships in the area.
- Satellite phone. If you have one, call the coastguard directly; the number should be programmed in.
- Prepare to abandon. Crew in lifejackets, liferaft ready, grab bag (with handheld VHF, PLBs, SART, flares) and the EPIRB.
- In the liferaft. EPIRB tied on outside, SART raised high, handheld VHF on Ch 16. Answer the aircraft or ship when they call.
The point: VHF DSC alone is not enough offshore. The EPIRB is your primary alerting tool beyond A1.
Worked Example: Man Overboard at Night, 12 Miles Offshore
At 0140 your crew member falls overboard, 12 miles south of the Lizard, in Force 5 and a lumpy sea, and you cannot find him in the dark. You are in A1 for a Falmouth Coastguard VHF coverage area. The immediate actions are to shout, press the MOB button on the plotter (which stores the position), throw the lifebuoy and light, and turn.
- The first radio act is the DSC distress alert, nature "man overboard", then the voice Mayday on Ch 16, including the MOB position and time, the casualty's details (lifejacket, light and PLB), and what you are doing.
- If the casualty has a PLB, the coastguard will receive his alert and locate him. If he has an AIS MOB beacon, your plotter will show his position and may sound an alarm.
- Coastguard directs resources and will ask other ships to keep a lookout. Ship-to-ship and on-scene communications are normally on Ch 16 or Ch 6 (international ship-to-ship search and rescue).
- If you recover the casualty, tell the coastguard immediately and give his condition, because the coastguard will ask whether you want a lifeboat or helicopter. Cancel the Mayday only on the coastguard's instructions.
The key lesson is that the DSC alert gets your position and identity to every set in range even if you are busy, and the voice message supplies the details the rescuers need.
Exam Tips
- Know the wording cold. Practise the Mayday, Pan-Pan and Securite messages aloud until you can do them without a card, then use the card anyway.
- Expect to be asked: what is Ch 70 used for, what is the range of VHF, what does the SART look like, how often do you self-test an EPIRB, what is the frequency of NAVTEX.
- Never press the distress button as a demonstration. Show the cover, say what you would do next, and describe the menu.
- Expect questions about the difference between EPIRB and PLB: the EPIRB is registered to the vessel and floats and activates itself (Category I), whereas a PLB is registered to a person and is activated by hand. Minimum operating life is 48 hours for an EPIRB and 24 hours for a PLB.
Summary
- GMDSS automates distress alerting. Sea areas A1 (VHF), A2 (MF), A3 (satellite) and A4 (polar) define the equipment needed.
- Priorities: Mayday (grave and imminent danger), Pan-Pan (urgency), Securite (safety), routine.
- In distress: DSC alert first, voice Mayday on Ch 16 about 15 seconds later, using MIPDANIO.
- On receiving a distress alert, listen, do not acknowledge by DSC unless directed, acknowledge by voice if appropriate, relay if needed, and proceed to assist.
- Cancel false alerts immediately by voice on Ch 16 and log them.
- NAVTEX on 518 kHz and SafetyNET via satellite deliver MSI; A, B and D messages cannot be rejected.
- Register your 406 MHz EPIRB, self-test monthly, watch battery and HRU dates, and keep it with you in the liferaft.
Check Your Understanding
- Define sea areas A1 and A2.
Answer: A1 is within VHF range of at least one coast station providing continuous DSC alerting, typically 20 to 30 miles. A2 is outside A1 but within range of an MF coast station with continuous DSC, typically 100 to 150 miles.
- In what order do you send a DSC alert and a voice Mayday, and how long do you wait between them?
Answer: DSC alert first on Ch 70 (sent automatically by the distress button), then the voice Mayday on Ch 16 after about 15 seconds, without waiting indefinitely for acknowledgement.
- What does MIPDANIO stand for?
Answer: Mayday (three times), Identity (name three times, call sign, MMSI), Position, Distress nature, Assistance required, Number of persons on board, Information (anything else useful), Over.
- Your DSC set alarms with a distress alert from a vessel 15 miles away, in A1. The coast station has not yet replied. What do you do?
Answer: Record the details and listen on Ch 16. Do not acknowledge by DSC unless directed by the coast station or RCC. Allow time for the coast station to acknowledge. If there is still no acknowledgement and you can help, acknowledge by voice on Ch 16 and inform the coastguard; if you cannot help, send a Mayday Relay. Log everything and proceed to assist if able.
- You accidentally press the distress button while cleaning the radio. What do you do?
Answer: Cancel using the set's cancel function or switch off, then on Ch 16 broadcast "All stations x3, this is (name x3, call sign, MMSI, position), cancel my distress alert of (date, time UTC)", and log it.
- What does the NAVTEX message identifier "EB12" mean?
Answer: Station E (Niton), subject B (meteorological warning, such as a gale warning), serial number 12.
- What checks should you make on a 406 MHz EPIRB before an offshore passage?
Answer: Registration up to date with correct vessel details and emergency contacts; monthly self-test carried out; battery and HRU expiry dates in date; bracket and float-free arrangement clear; lanyard attached; crew briefed on how to activate it.
- When should you use Pan-Pan rather than Mayday? Give an example.
Answer: When there is an urgent safety problem with the vessel or a person, but no grave and imminent danger. For example: engine failure and a fouled rudder 10 miles offshore in moderate weather, needing a tow; or a crew member with a suspected broken arm needing medical advice (Pan-Pan medico).
- What is the purpose of a SART, and how does it appear on radar?
Answer: It allows searching vessels and aircraft to locate a liferaft. When interrogated by X-band (9 GHz) radar it transmits a response that shows as a line of 12 dots outward from its position, becoming arcs and then circles at close range.
- Why is VHF DSC alone insufficient for alerting on a passage across the Western Approaches?
Answer: VHF is line-of-sight, giving about 20 to 30 miles to a coast station. Well offshore no coast station will hear the alert, and only ships within a few miles might. An EPIRB (via satellite), a satellite phone, Inmarsat C or MF/HF DSC is needed to reach the rescue services.
- A crew member falls overboard at night and cannot be seen. What is the first radio action and what must the voice message include?
Answer: A DSC distress alert (nature: man overboard), followed by a voice Mayday on Ch 16 giving the vessel's identity, the MOB position and time, number of persons on board, the casualty's description and any beacon or light, and actions being taken. Stay on watch.
- How do you decide whether an EPIRB is fit for an offshore passage, and what is the typical minimum operating life of an EPIRB and a PLB?
Answer: It is registered with current details, passes its self-test, has an in-date battery and HRU, is correctly mounted and clear, and the crew know how to activate it. An EPIRB must operate for at least 48 hours and a PLB for at least 24 hours.