How to Use a VHF Radio: Channels, Mayday and the Licence Question

Why the Radio Beats the Phone

A mobile phone is a private line to one number. Out on the water that is three problems at once. It needs a signal, and coverage fades within a few miles of most coasts and inside anything with a steel hull. It reaches one person, who has to be awake, answer, understand where you are and then ring somebody else. And it tells nobody nearby that you are in trouble.

The VHF fixes all three. It needs no network, only line of sight between two antennas. Everything you say goes to every set in range, so the fishing boat a mile off and the ferry in the channel hear the same Mayday at the same moment the coastguard does, and one of them is almost always closer than the lifeboat. And the coastguard can find you even if you cannot say where you are: coastal stations in the US (the Coast Guard's Rescue 21 network) and in the UK carry direction-finding equipment that takes bearings on a channel 16 transmission from two or more sites and fixes the position where they cross.

Range is the trade-off. VHF is line of sight: a fixed set with a masthead antenna reaches a coastguard aerial at roughly 20–25 nautical miles, a handheld reaches another handheld at about 5 nm. None of it depends on a network being up, which is the point.

Channel 16, Dual Watch and the Working Channels

Channel 16 does two jobs: distress and calling. Every coastguard station keeps a continuous watch on it, every ship at sea is required to, and so should you whenever you are under way. It is the channel you call another boat on, and the channel you never hold a conversation on. Call, agree a working channel, switch. Radio checks and testing on 16 are prohibited in many countries (in the US, use channel 9 or an automated radio check service), and the coastguard will tell you off for chatter.

Dual watch (or tri-watch) is the feature that makes this practical. Set it, pick a working channel, and the radio flicks back to 16 every couple of seconds to check for traffic. If someone calls on 16 you hear it; otherwise you stay on the channel you chose. For a boat cruising in company with another, that means 16 plus 72 all day.

The working channels are where the US and international plans part company; the table above is the short version. Internationally, ship-to-ship on 72 or 77 and a marina on 80 (in the UK) or whatever the almanac lists; in the US, call on 9, ship-to-ship on 68, 69, 71, 72 or 78A, and bridge-to-bridge on 13 at low power. Channel 70 is the one to understand rather than use: it is the digital channel that DSC works on, voice is locked out, and the only time you will “use” it is when you press the red button.

The Licence Question

Two separate things are licensed: the radio and the person. Which you need depends on the country whose flag the boat flies, not on where you happen to be, and the answers differ sharply.

• United Kingdom. The set needs a Ship Radio Licence from Ofcom (free, online, covers the fixed VHF, DSC, AIS, radar and EPIRB). The operator needs a Short Range Certificate (SRC), the one-day RYA course that covers exactly the procedures below. A DSC handheld can carry its own Ship Portable Radio Licence and MMSI. Using a VHF without both is an offence.
• United States. A recreational boat in US waters needs no station licence and no operator permit; the FCC exempted “voluntary ships”. The exemption ends at the border: sail to the Bahamas, Mexico or a Canadian marina and you need an FCC Ship Station Licence and a Restricted Radiotelephone Operator Permit, paperwork rather than exams.
• Everywhere else. Canada requires a Restricted Operator Certificate (Maritime); Australia a marine operator certificate; most European countries an SRC-equivalent. Charter companies will ask to see it. The national telecoms regulator's website is the source, not a forum.

The MMSI, and why the red button is useless without it

Every DSC radio needs a Maritime Mobile Service Identity: a nine-digit number, the first three digits of which identify the country (232–235 for the UK, 338 and 366–369 for the US). It is programmed into the set once (most radios lock after one or two entries, so type carefully) and registered against your boat: name, type, length, colour, people usually aboard, an emergency contact ashore.

When you hold the red button, the radio sends that number and, if it has a GPS feed, your position, on channel 70. Every DSC set in range alarms. The coastguard looks the number up. If it is registered, they have your boat's description and a phone number for someone who knows where you were going before you have finished saying your name on 16. If it is not registered, they have a number and a dot on a screen. If the set has no GPS connected, they have a number and nothing else. A DSC radio with the GPS wire left off and an unregistered MMSI is an expensive way of pressing a button that says “somebody, somewhere”.

In the UK the MMSI comes with the Ship Radio Licence. In the US a boat that stays in domestic waters can get one free from BoatUS or the US Power Squadrons, but those numbers are not passed into the international database, so a boat going abroad needs the FCC-issued MMSI that comes with the station licence. Connect the GPS: modern sets have one built in or take a feed from the chartplotter over NMEA 0183 or NMEA 2000, and a position on the screen is the proof it is working.

The Calling Procedure

A routine call has a shape so that the other boat knows who is being called, who is calling and when to speak. Listen first; if the channel is busy, wait. Press the button, pause a second, then speak across the microphone rather than into it.

“Marina Bay Yacht Harbour, Marina Bay Yacht Harbour, Marina Bay Yacht Harbour. This is sailing yacht Kestrel, Kestrel, Kestrel. Over.” The called station up to three times, “this is”, your name up to three times, “over”. Release the button. They answer: “Kestrel, this is Marina Bay. Go to channel 80. Over.” You confirm the channel, both switch, the conversation happens off 16, and it ends with “Out.” On a working channel, or with a boat you talk to daily, once each is enough.

The words carry meaning. Over means “I have finished, your turn.” Out means “I have finished, the conversation is over.” They are opposites, which is why “over and out” is film dialogue. Say again means repeat. Roger means received; Wilco means received and I will do it. Spell names phonetically, say numbers digit by digit, and keep it short: the channel is shared with everyone within 20 miles.

Etiquette is the same idea repeated. Nothing on 16 beyond a call and a switch. No profanity: it is an offence, and the coastguard records everything. No hoax or test distress calls, which are prosecuted. And keep the set on: a radio switched off to save the battery will not hear the boat behind you calling to say your dinghy has come adrift.

Mayday, Pan-Pan and Sécurité

Three prefixes, three levels, and the coastguard's response is scaled to the word you choose. Use the right one. A Pan-Pan for a dead engine off a lee shore is honest and gets a lifeboat on standby; a Mayday for the same thing on a calm day with an anchor down is not. And a real Mayday said hesitantly, without the word, may get a polite “say again” instead of a helicopter.

Making the Mayday

A Mayday is for grave and imminent danger to the boat or a life. The order is fixed because rescuers need the information in that order: who, where, what, what you need, how many. The RYA teaches it as a mnemonic (Mayday, Identity, Position, Distress, Assistance, Number, Information, Over); keep a card by the set with the boat's name and the blanks, because the person making the call is often not the skipper.

1. Switch to high power and channel 16. If the set has DSC, lift the cover and hold the DISTRESS button for about five seconds until it confirms. The set sends the alert and switches to 16 itself.
2. “MAYDAY, MAYDAY, MAYDAY. This is Kestrel, Kestrel, Kestrel. MAYDAY, Kestrel. My position is five zero degrees four two decimal three minutes north, zero zero one degrees one five decimal eight minutes west (or: two miles south-west of Portland Bill). We are taking on water and sinking. I require immediate assistance. Four persons on board. We are a white 11 m sloop, abandoning to the liferaft. Over.”
3. Release the button and listen. If there is no answer within a minute, say it again. Do not change channel. Keep the set on and one person beside it.

A position from the GPS is best. A bearing and distance from something on the chart is second best. “Near the harbour” is not a position. And if the emergency passes, cancel it: a Mayday that is not cancelled keeps a lifeboat at sea looking for you.

Pan-Pan and Sécurité

Pan-pan is the urgency call: something is seriously wrong but nobody is about to die, which is the honest description of most situations people reach for Mayday in. Engine stopped and drifting towards the shore; a suspected broken arm and you want a doctor's advice through the coastguard; a crew member back aboard after falling in and now cold. Same structure as a Mayday, prefix spoken three times, and in the assistance line you say what you actually want. Sécurité (“say-cure-ee-tay”) is a broadcast about a hazard rather than a request for help: you announce it on 16 and read the message on a working channel so that 16 stays clear. Coastguard stations use the same form for gale and navigation warnings at fixed times, which is why a set left on 16 hears the weather without asking for it.

If you hear a Mayday

Stop transmitting. Listen. Write down the boat's name, position, time and problem in the log; you may be the only one who caught it clearly. Wait for the coastguard to acknowledge. If they do not, and you can help or pass it on, answer the casualty and broadcast a Mayday Relay: “MAYDAY RELAY, MAYDAY RELAY, MAYDAY RELAY. This is [your name x3]. The following received from [casualty] at [time]” followed by their message. Do the same for a boat in distress that has not called at all.

The coastguard may impose radio silence with “Seelonce Mayday” (the French silence). Then nobody transmits on 16 except the casualty and the rescuers until “Seelonce feenee” lifts it. If you hear either, the only correct thing to do is listen.

Squelch, Power and the Antenna

Squelch is the knob that silences the hiss when nobody is transmitting. Turn it down until the hiss comes on, then up until it just stops, and leave it there. Too high and a weak, distant call is cut off before you hear it; a set that has gone strangely quiet for hours often just has the squelch wound up.

Power is a two-position switch: 1 W and 25 W on a fixed set, around 1 W and 5–6 W on a handheld. Low power is for the marina, the boat alongside and channel 13 in the US. High power is for distance and for any distress call. Left on high in a crowded harbour, every boat for twenty miles listens to you ask for a berth.

The antenna beats the wattage. Because VHF is line of sight, the horizon is the limit and the horizon is set by height. The radio horizon in nautical miles is roughly 2.2 times the square root of the antenna height in metres, for each end. A masthead at 15 m reaches about 8.5 nm; a handheld at 2 m about 3 nm; a coastguard aerial on a 100 m headland about 22 nm. Add the two ends: masthead to coastguard about 30 nm, handheld to handheld about 6 nm. Going from 5 W to 25 W makes the signal stronger at the edge but does not move the edge. Raising the antenna does. Check the coax connectors once a season for green corrosion; a bad connector throws away more range than any power setting.

AIS on the VHF

AIS is another VHF signal: ships and many yachts transmit name, position, course and speed on two dedicated channels, and anything with a receiver plots them. Many fixed sets now have an AIS receiver built in and show targets on their own screen or pass them to the chartplotter, a cheap way to see the ferry behind the headland before you see the ferry. The useful trick is that a target comes with an MMSI, so you can call the ship directly by DSC and her bridge alarm sounds, rather than hoping a watch officer picks out “the ship off my starboard bow”. A receiver only listens; a Class B transponder is a separate box that also transmits your own data.

Handheld vs Fixed: the Backup in the Grab Bag

A fixed set with a masthead antenna is the radio that reaches the coastguard. A handheld is the radio that comes with you. For a kayak, a paddleboard, a jet ski or a tender it may be the only radio; for a cruising boat it is the one you take into the liferaft. Buy one that floats, is rated IPX7 or IPX8 and, if the budget allows, has its own GPS and DSC: hold the red button and the coastguard gets your position from a liferaft, which no fixed set can do once the boat has gone. Charge it and keep it in the grab bag next to the EPIRB, and remember that its range to another handheld is around 5 nm. It is also the radio you hand to the crew in the dinghy who said they would be back by nine.

The Two Things Left Switched On

At anchor for the night, the boat goes quiet. The plotter is off, the engine is cold, the lights are down to the anchor light. Two things stay on. The VHF, on 16 at a volume that will wake you, because the boat that drags onto you at three in the morning will call before she hits, and the gale warning comes on the same channel. And the anchor alarm, because the one thing the radio cannot tell you is that your own boat is the one moving. They do the same job from opposite ends: the radio hears everyone within twenty miles, the alarm watches the twenty metres under your keel. With both running you can sleep; with the radio off, the yacht upwind loses her anchor and you find out by feel.

The Bottom Line

The VHF is a broadcast, not a phone call, and that is the point of it: the boat two miles off hears you before the coastguard does, and is usually the one that arrives first. Leave it on 16 with dual watch. Register the MMSI and connect the GPS, or the red button sends a number nobody can read. Call with the name three times, “this is”, over, and never “over and out”. Know the Mayday by heart in its fixed order and use Pan-Pan for everything that is urgent but not fatal. Put the antenna as high as you can and stop worrying about watts. And keep a floating handheld in the grab bag, because the radio that saves you is the one that is still with you when the boat is not.