VHF marine radio is the primary communication tool in coastal waters and the primary emergency signaling system for vessels in distress. Knowing how to use it correctly — which channels to use for which purposes, how to structure a call, and what to say in an emergency — is not a formality. A correctly executed MAYDAY call can reduce rescue response time by minutes that matter. An incorrect call, or a failure to transmit at all because the operator does not know the procedure, can be the difference between a timely rescue and a prolonged search.
Channel 16: The Watch Channel
Channel 16 (156.800 MHz) is the international distress, safety, and calling channel. It is monitored continuously by the US Coast Guard, commercial vessels of any significance, and by recreational mariners who follow proper practice. Keeping watch on channel 16 while underway is a requirement for commercial vessels and a strong operational practice for recreational vessels — in most coastal areas, it is also required by law for any vessel equipped with a VHF radio.
All initial calls are made on channel 16. The calling station hails the station it wants to reach, both parties agree to a working channel, and the conversation moves to that working channel. Channel 16 is not the channel for the conversation — it is the channel for making contact. Holding extended conversations on 16 ties up the frequency and blocks distress traffic.
The procedural sequence: listen to confirm channel 16 is clear. Transmit your call. If no response within 30 seconds, transmit again. If no response after three attempts over two minutes, the station is not available on 16 at this time. Do not keep calling indefinitely — you are occupying the frequency that distress calls use.
Working Channels: What to Use and What to Avoid
Once contact is established on channel 16, both parties switch to an agreed working channel for the actual communication. The standard working channels for recreational vessels in US waters are:
Channel 9 — Designated as an alternative recreational calling channel in some regions. This allows recreational vessels to hail each other on 9 while keeping 16 clear for commercial and distress traffic. Usage of channel 9 as a hailing channel varies by region; on the Great Lakes and some inland waters it is common. On the East Coast, most recreational vessels hail on 16 and move to a recreational working channel.
Channels 68, 69, 71, 72, and 78A — The primary recreational working channels. These are allocated for non-commercial vessel-to-vessel communications and for communication with marinas and other recreational facilities. When a marina tells you to switch to channel 68, this is why. Any of these channels can be used for a recreational working conversation; pick one that is not in use.
Channel 22A — USCG working channel. The Coast Guard uses this for communications with recreational vessels after initial contact on 16. It is not a recreational vessel-to-vessel working channel. Do not use it to call another boat or a marina; it is reserved for Coast Guard traffic.
Channels 6, 8, 11, and 14 — Commercial/commercial traffic channels. Avoid these for recreational communications. Channel 6 is the intership safety channel for certain purposes; channels 8, 11, and 14 are commercial traffic channels used by commercial shipping, tug-barge operations, and port authority communications.
Channel 70 — DSC (Digital Selective Calling) only. No voice communications on channel 70. This is the digital distress and calling channel, explained below.
The Call Sequence: How to Hail a Vessel or Marina
A properly structured VHF call identifies the called station, identifies the calling station, and ends with the procedural word "over" when you expect a reply. The format is simple and consistent. Deviating from it — using casual language, failing to identify both stations, or not saying "over" — is not just bad form. It causes confusion, requires repetition, and creates ambiguity about whether a transmission is finished.
To call a marina: transmit on channel 16. Say the marina's name twice, then your vessel name twice, then "over." The full call: "Annapolis Harbor Master, Annapolis Harbor Master, this is sailing vessel Nomad, sailing vessel Nomad, over." The marina responds, agrees to a working channel: "Nomad, Annapolis Harbor Master, switch to six-eight, over." You respond: "Six-eight, Nomad, out." Both parties switch to channel 68 and the substantive conversation begins there.
To call another vessel: same format. Two calls of the vessel name, your vessel name twice, "over." If the other vessel responds and wants to talk, they suggest a working channel. Both switch. The conversation happens on the working channel. When the conversation is finished, both parties say "out" — not "over and out," which is a contradiction (over means "I expect a reply"; out means "transmission complete, no reply expected"). Use one or the other, not both.
When responding to a call directed at you: confirm the working channel, then end your response with "over" to hand the conversation back to the calling station. On the working channel, use normal give-and-take conversational practice, but maintain the habit of ending each transmission with "over" when you expect the other party to respond.
MAYDAY: Immediate Danger to Life
MAYDAY is the international distress signal. It is used only when there is grave and imminent danger to a vessel or person requiring immediate assistance. Sinking, fire aboard, medical emergency that requires evacuation, or any situation where lives are immediately at risk. MAYDAY is not used for a mechanical breakdown that leaves you drifting — that is a Pan-Pan situation unless the drift is putting you onto rocks with people in danger of going overboard.
The MAYDAY call is transmitted on channel 16 at high power (25 watts). The format:
Say "MAYDAY" three times. Then say "this is" followed by your vessel name three times and your call sign or MMSI number. Then give your position as precisely as possible — GPS coordinates if you have them, or a bearing and distance from a known landmark ("three miles west of Montauk Point"). State the nature of the distress. State the number of persons aboard. Give a brief description of your vessel — length, type, hull color, any notable features that will help searchers identify you. Say "over."
Full example: "MAYDAY, MAYDAY, MAYDAY. This is sailing vessel Wanderer, sailing vessel Wanderer, sailing vessel Wanderer, MMSI 338123456. MAYDAY. Position 41 degrees 04 minutes north, 71 degrees 57 minutes west. We are taking on water rapidly and sinking. Four persons aboard. We are a 38-foot white sloop with a blue bimini. Abandoning to life raft. MAYDAY. Over."
Then listen. The Coast Guard will acknowledge on 16 and direct further communications. If there is no response within one minute, transmit the MAYDAY again. Continue transmitting until you receive an acknowledgment.
If you hear a MAYDAY and the Coast Guard does not acknowledge within one minute, any vessel may — and should — acknowledge the MAYDAY themselves and report it to the Coast Guard. The relay procedure: transmit "MAYDAY relay, MAYDAY relay, MAYDAY relay, this is [your vessel], I am relaying a distress message" and repeat the distress information you heard.
Pan-Pan: Urgent but Not Immediately Life-Threatening
Pan-Pan (pronounced "pahn pahn") is the urgency signal, one level below MAYDAY. It is used for situations requiring assistance that are serious but do not involve immediate danger to life: a medical situation on board that requires advice or non-emergency evacuation, a vessel that has lost power and is drifting but not in immediate danger, or a person in the water who has been recovered but needs medical attention. The format is the same as MAYDAY but substitutes "PAN-PAN" for "MAYDAY," repeated three times at the beginning of the call.
The important distinction: if there is any doubt whether a situation is a MAYDAY or a Pan-Pan, call MAYDAY. You will not be prosecuted for upgrading a Pan-Pan situation to a MAYDAY in good faith. The consequences of under-calling are worse than the consequences of over-calling.
Securité: Safety Broadcasts
Securité (pronounced "say-cure-ee-tay") is the safety signal used for broadcasting navigational hazards. A large ship entering a channel will broadcast a Securité call on channel 16 (or the appropriate working channel for that waterway) to alert smaller vessels of its presence and request they keep clear. The USCG broadcasts Securité calls for navigation hazards — a buoy off station, a debris field, a vessel adrift. The format: say "SECURITE" three times, then transmit the safety information. Vessels receiving a Securité call are not required to respond, but should take appropriate action based on the content.
Radio Checks: How to Test Your Radio Correctly
Testing whether your VHF is transmitting correctly is a standard and necessary practice. The incorrect way to do it — which triggers emergency responses — is to say "MAYDAY test" or any variation. Never use the word MAYDAY in any context other than an actual distress call. The Coast Guard is required to respond to any MAYDAY transmission, and test calls create unnecessary emergency response and clog distress frequencies.
The correct way to do a radio check is to call a local marina or the USCG on channel 16 and say: "[Station name], [Station name], this is [your vessel], radio check, over." The responding station will tell you whether your signal is readable and at what quality level (the standard five-point scale: 1 = barely readable, 5 = perfectly readable, with corresponding descriptions). Many marinas and the Coast Guard are willing to provide radio checks as a service. Some areas have dedicated VHF users groups that maintain listening watches specifically for radio check responses.
Alternatively, subscribe to a VHF/AIS monitoring service. Some chartplotter systems can confirm your AIS transmission is being received, which verifies your radio is working at the power level required for AIS (1 watt on 161 MHz, different from voice VHF but on the same radio in most modern units).
DSC: Digital Selective Calling and the MMSI
Digital Selective Calling (DSC) is a digital protocol built into most modern VHF radios that allows automated distress signals to be sent over channel 70. The DSC distress button — typically a red, covered button on the face of the radio — when held down for five seconds, transmits a digital distress alert that includes your vessel's MMSI (Maritime Mobile Service Identity) number and, if the radio is connected to a GPS source, your position and the time. The alert goes to the Coast Guard and any DSC-equipped vessel within VHF range simultaneously.
For DSC to function correctly, two things are required. First, your MMSI number must be programmed into the radio. The MMSI is a nine-digit number unique to your vessel; it is how the Coast Guard looks up your vessel information (name, description, registered owner, emergency contacts) when they receive your distress alert. US vessels can obtain an MMSI free of charge through BoatUS (a free membership-based registration) or through the FCC license process. Program the MMSI into your radio before you go offshore — an unprogrammed DSC radio transmits a distress alert with no vessel identification, which significantly delays rescue response.
Second, connect the radio to a GPS source so that the distress alert includes position. Most modern VHF radios have a GPS NMEA input port for this purpose. A GPS-connected DSC alert tells the Coast Guard exactly where you are at the moment of distress. An unconnected DSC radio transmits the alert but with no position — still better than nothing, but the rescue search area is larger.
After pressing the DSC distress button, remain on channel 16 and listen. The Coast Guard will acknowledge the DSC alert and initiate voice contact on 16. Your voice call on 16 following the DSC alert should follow the standard MAYDAY format, confirming your position, the nature of the distress, and the number of persons aboard.