Share Your Location at Sea

VHF Channel 16 first — and why not just a phone

At sea, the phone in your pocket is the wrong first instrument. A VHF distress call on Channel 16 (156.8 MHz) is heard by the coastguard and every vessel within range at the same time — and the nearest help is usually a boat a mile away, not a lifeboat station an hour out. Rescue services can also direction-find a VHF transmission; nobody can direction-find your phone call. Mobile coverage dies within a few miles of the coast, calls drop mid-sentence, and a call connects you to one operator instead of alerting everyone afloat.

The phone is the backup, and it's a good one close inshore: keep it in a waterproof pouch on your person (not in the cabin), make a voice call rather than trusting a text or a map-app pin, and know your country's route to the coastguard — in the UK and Ireland dial 999 or 112 and ask for the Coastguard. Emergency calls can use any network's signal, so try even with no bars showing. And before you dial anything, get the position on screen with the tool above — it works with no signal at all, because GPS is receive-only and needs no network.

The Mayday call, line by line

“Mayday” is reserved for grave and imminent danger to a vessel or a life. The structure below is the international one — it survives panic precisely because it's a fixed script, and the builder in the tool above fills it in with your live position:

MAYDAY, MAYDAY, MAYDAY — the alarm itself, three times.
THIS IS [boat name] × 3 — who is calling, repeated so a weak signal still carries it.
MAYDAY [boat name] — once more, formally.
MY POSITION IS… — latitude then longitude, degrees and decimal minutes, digit by digit. Position is the single most valuable line in the call; give it before anything else can go wrong.
Nature of distress — taking on water, fire, collision, medical.
Persons on board — so rescuers know when everyone is accounted for.
I REQUIRE IMMEDIATE ASSISTANCE… OVER — then release the button and listen.

Lesser emergencies use different openings — Pan-Pan for urgency without immediate danger, Sécurité for safety broadcasts. Our Mayday, Pan-Pan and Sécurité article walks through all three and when each applies.

DSC — the red button that calls everyone at once

Modern fixed and many handheld VHF sets carry Digital Selective Calling: lift the flap, hold the red DISTRESS button for five seconds, and the radio transmits a digital alert on Channel 70 carrying your vessel's MMSI (its nine-digit radio identity) and — if the radio is connected to GPS or has it built in — your position, to the coastguard and every DSC-equipped vessel in range. Receiving sets sound an alarm their crews cannot ignore. It is the single best button on the boat, with two conditions attached.

First, the MMSI only means something if the radio is registered — that's what links the number to your vessel's name, description and your shore contact. Second, the position only goes out if the GPS feed is actually connected — the classic surveyor's finding is a DSC radio installed for years with the NMEA wire never joined. Press-and-hold is step one; the voice Mayday on Channel 16 immediately after is still expected, because the digital alert opens the door and the voice call tells rescuers what's wrong.

EPIRBs and PLBs — registration is the rescue

Beyond VHF range, the satellite beacons take over. An EPIRB is registered to the vessel, floats upright, activates automatically in water and transmits on 406 MHz to the Cospas-Sarsat satellite system for 48 hours or more; a PLB is the pocket version, registered to a person, manually activated, with at least 24 hours of transmission. Both give search and rescue a global-coverage alert with your identity and — on modern GPS-equipped beacons — your position to within a hundred metres or so.

The part people skip is the part that matters: registration is free and it is the rescue. An unregistered beacon is an anonymous scream — coordinators see an alert with no boat name, no description, no phone number to call and no way to rule out a false alarm quickly. Register (and re-register when details change) with your national authority: in the UK at register-406-beacons.service.gov.uk (registration is mandatory for UK vessels), in the US with NOAA at beaconregistration.noaa.gov. It takes minutes, costs nothing, and turns a distress signal into a search with a name on it.

Spell it so it survives the static

Radio channels chew up ordinary speech. The NATO alphabet and the ITU figure pronunciations exist so a boat name and a position survive a bad channel — niner because “nine” and “five” blur, decimal because “point” disappears:

• A Alfa
• B Bravo
• C Charlie
• D Delta
• E Echo
• F Foxtrot
• G Golf
• H Hotel
• I India
• J Juliett
• K Kilo
• L Lima
• M Mike
• N November
• O Oscar
• P Papa
• Q Quebec
• R Romeo
• S Sierra
• T Tango
• U Uniform
• V Victor
• W Whiskey
• X X-ray
• Y Yankee
• Z Zulu

• 0 Zero
• 1 Wun
• 2 Too
• 3 Tree
• 4 Fower
• 5 Fife
• 6 Six
• 7 Seven
• 8 Ait
• 9 Niner
• . Decimal

Practice reading your home berth's position aloud once — latitude then longitude, the word “decimal” where the point falls, hemisphere letters last (“north… west”). The readout line in the tool above does the spelling for you, and thirty seconds of practice makes the real thing automatic.

If the worst happens, stay with the boat

Search aircraft and lifeboats find boats, not heads in the water. Even swamped or capsized, a hull is a bigger radar and visual target than a person, it's flotation you don't have to work for, and it marks the position you just transmitted — swimming for a shore that looks closer than it is has ended badly for strong swimmers in warm seas, never mind cold ones. Lifejackets go on before the emergency, not during; in cold water, the first minute of gasping (cold-shock) is survived by floating on your back and doing nothing, not by swimming hard.

The same logic drives everything on this page: transmit early while the mast is dry, give the position first, then fight the fire or the leak. A Mayday that turns out unnecessary is cancelled with one call; the one you delayed is the one that gets found by drift modelling instead of by radio. If you'd like the coastal-hiking equivalent of this page for land emergencies, that's share location in an emergency.