Most skippers rehearse the mechanics of reefing or man overboard drills far more often than they rehearse the one radio call that actually brings help. A distress call is a procedure, not an improvisation, and the DSC button on your VHF only does half the work. The rest is a voice message that has to be clear enough for a MRCC watchkeeper to dispatch assets in the right direction, on the right frequency, without asking you to repeat yourself while your boat is filling with water.

When Mayday is the right call

Mayday is reserved for grave and imminent danger to a vessel or a person, requiring immediate assistance. Fire on board, a hull breach you cannot stem, a crewmember in cardiac arrest, dismasting with injuries, a serious grounding on a falling tide with weather building. If you are asking yourself whether the situation qualifies, it very often does.

Below that threshold, you have two other levels:

  • Pan-Pan : urgency. A serious situation concerning the safety of a vessel or person, but no immediate danger to life. Loss of propulsion in a shipping lane, a medical issue that needs advice, steering failure in fair weather.
  • Sécurité : safety. Navigational or meteorological warnings. Rarely something you originate as a leisure skipper, but you will hear it constantly from coastguards.

Getting the level right matters. Calling Mayday for a flat battery burns credibility and clogs a channel that someone else may need in the next ten minutes. Calling Pan-Pan when you actually have water over the floorboards costs you the immediate SAR response that a Mayday triggers automatically.

What DSC actually does when you press the button

Digital Selective Calling is the reason modern VHF distress works. Lift the red guard, press and hold the distress button for roughly five seconds, and the radio transmits a digital burst on channel 70 containing your MMSI, your GPS position and time, and (if you selected one) the nature of distress. Every DSC-equipped station within range, including coastguards and commercial traffic, gets an audible alert and your details on screen. Your radio then switches automatically to channel 16 and waits for you to speak.

Three details are worth checking now, not later :

  • Your VHF must have a valid MMSI programmed. An unprogrammed radio sends "000000000" and coastguards cannot identify you. Most sets only allow one MMSI entry without a factory reset.
  • Your VHF must have a GPS fix, either from an internal receiver or from a plotter feed over NMEA. Without position, DSC still transmits your MMSI, but SAR loses precious minutes triangulating you.
  • The DSC button must be held long enough. A quick tap usually pre-arms the alert. You need the full countdown to actually send it.

If you have never confirmed how your radio is wired and configured, our walk-through on how to properly configure your VHF for security is worth ten minutes at the chart table before you leave the pontoon.

The Mayday voice message, word for word

After the DSC alert, you speak on channel 16. The format is fixed and it exists because a stressed brain remembers structure. Tape a copy near the radio. The standard call is:

  1. "Mayday, Mayday, Mayday."
  2. "This is [vessel name, spoken three times], [MMSI], [callsign if you have one]."
  3. "Mayday, [vessel name once], [MMSI]."
  4. Position : latitude and longitude, or bearing and distance from a charted mark. Read the coordinates slowly, digit by digit.
  5. Nature of distress : "sinking after collision", "fire in engine compartment", "man overboard, not recovered".
  6. Assistance required : "require immediate evacuation", "require pumps and medical assistance".
  7. Number of persons on board and any injuries.
  8. Any other useful information : abandoning to liferaft, EPIRB activated, boat description and colour, drift direction.
  9. "Over."

Then release the transmit button and listen. A coast station will normally acknowledge within seconds. If nothing comes back within about 15 seconds, repeat the entire message. If still nothing, try channel 16 on low power to reach a nearby vessel, or step down to channel 06 or 08 for inter-ship. Do not assume silence means no one heard you. On the French Atlantic coast, CROSS relays are dense. In more remote cruising grounds, another yacht is often your best relay.

Mayday relay: when the distress is not yours

You will more likely hear a Mayday than send one. If a MRCC is already acknowledging it, stay off the channel and listen. If you hear a distress call that goes unanswered, you are obliged to relay it. The format mirrors the original :

"Mayday relay, Mayday relay, Mayday relay. This is [your vessel name, three times], [MMSI]. Received the following Mayday from [vessel name], on [time], position [coordinates], nature of distress [detail]. Over."

Your DSC can also send a distress relay call, which is a separate menu item on most sets. Use it if you are witnessing another vessel's emergency, for example a nearby boat on fire that has no working radio. Never press your own distress button on someone else's behalf : it identifies your MMSI as the vessel in danger and confuses the SAR picture.

What the radio cannot do alone

VHF is line of sight. From a mast-top antenna at 15 metres, expect 25 to 40 nautical miles to a coastguard station, less from a handheld at cockpit height. Beyond that, DSC on VHF is not enough. This is where a second layer of alerting matters, and where the choice between an EPIRB, a PLB or an AIS MOB beacon becomes concrete. If you have not made that call for your boat, our comparison of EPIRB, PLB and AIS distress beacons lays out which one fits which kind of sailing.

For genuinely offshore passages, VHF DSC is a coastal tool. You will also want a way to talk to a rescue coordinator, not just alert one. Our overview of satellite communicators for offshore sailing covers the practical trade-offs between Iridium, inReach and the newer options.

Two other tools sit alongside the radio and often get forgotten in the panic :

  • Visual signals. Once help is close, guiding it to you is a separate skill. Know how to use a distress flare safely before you need to fire one from a heaving cockpit.
  • AIS. If your MMSI is programmed and you are transmitting AIS, SAR assets will see you before they see your hull. That same picture works the other way : reading AIS well tells you which commercial vessel is closest and best placed to assist.

Drills, cancellations and false alerts

Two rules that experienced skippers occasionally forget :

Cancel a false alert immediately. If you press the distress button by accident, do not switch the radio off. That is the worst response, because it leaves an unresolved distress alert in the system and commits SAR assets to searching for a vessel that is fine. Instead, stay on channel 16 and transmit : "All stations, all stations, all stations, this is [vessel name], [MMSI], position [coordinates]. Cancel my distress alert of [time]. No distress. Out." Repeat if needed. Log the incident.

Drill it, quietly. Once a season, at the dock, with the antenna disconnected or the radio in a documented test mode, run through the voice script with your crew. Show every person on board where the radio is, how to unclip the microphone, what the red guard looks like, and how to read the boat's position off the plotter. On a charter boat, this belongs in the safety briefing alongside liferaft and vest checks. Speaking of which, the common mistakes with automatic vests tend to surface at exactly the same moment as a botched Mayday.

The core skill here is simple : press, hold, speak the script. What makes it work under pressure is knowing your MMSI is correct, your GPS is feeding the radio, your crew has heard the words before, and your position appears the instant you glance at the plotter. That last part, having a clean, current position and a boat state you can describe in one sentence, is precisely what the Oria Box keeps ready in the background. If a Mayday call is the last thing you ever want to make, it is also the one worth rehearsing before the season starts.