Using a VHF Radio: Proper Procedure and Mayday Calls

VHF marine radio is the single most important communication system a recreational sailor can carry. The U.S. Coast Guard Navigation Center states that before purchasing anything else, boaters should make sure they have a VHF marine radio. Proper procedure—from routine calling to a MAYDAY distress call—determines whether your transmission is heard, understood, and acted upon. This article explains the core procedures, common mistakes, and safety framework for using VHF radio correctly.

Main Explanation

What it is

VHF (Very High Frequency) marine radio operates on designated maritime channels between 156 and 162 MHz. It is a line-of-sight system, meaning range depends on antenna height—typically 5 to 20 miles for recreational boats, and up to 60+ miles for tall sailboat masts. Proper procedure includes selecting the correct channel, using accepted prowords, listening before transmitting, and following distress, urgency, and safety call formats. A MAYDAY call is the most serious call you can make from a vessel; it signals grave and imminent danger and requires immediate assistance.

In this context, “proper procedure” is not tied to any specific boat brand, sailing school, or equipment manufacturer. It is a standardized set of practices defined by maritime authorities such as the U.S. Coast Guard and Maritime New Zealand, and reinforced by practical seamanship guides. The goal is consistent, recognizable communication that works across languages and experience levels.

Why it matters

Marine VHF channels are shared, and poor procedure creates interference that can block distress traffic. Maritime New Zealand’s Radio Handbook warns that open microphones are the main cause of serious interference on VHF channels. Conflicting advice from forums, outdated manuals, and casual habits can lead to confusion when seconds count. The stakes are high: a missed MAYDAY, a garbled position, or a transmission on the wrong channel can delay rescue. Reliable, independent reference material helps sailors cut through information overload and follow a consistent, recognized procedure.

Unlike cellphones, VHF radios work reliably offshore, broadcast to all nearby vessels simultaneously, and connect directly to Coast Guard rescue coordination centers. When seconds count, VHF is the communication tool that saves lives. But that only works if the operator follows the correct procedure.

How it works

VHF radios use specific channels for specific purposes. Channel 16 is the international distress, safety, and calling channel. Channel 9 is often used as a hailing channel for recreational boaters. Digital Selective Calling (DSC) allows a one-button distress alert that transmits your vessel’s identity and, if connected to GPS, your position. The MAYDAY voice procedure follows a fixed order: “MAYDAY, MAYDAY, MAYDAY,” then “THIS IS [vessel name three times + callsign/MMSI],” then repeat MAYDAY and vessel name once, then give position, nature of distress, number of people aboard, and assistance required, ending with “OVER.”

Radio watchkeeping regulations require vessels with VHF to maintain a listening watch on Channel 16 when underway, unless communicating on another channel. Always listen before transmitting to avoid causing interference. Use accepted prowords: “OVER” means you have finished your transmission and expect a reply; “OUT” means the conversation is finished; “ROGER” means message received; “SAY AGAIN” means repeat your last transmission; “STAND BY” means wait.

How to do it

For a MAYDAY call: (1) If fitted, press and hold the red DSC distress button for 5 seconds. (2) Switch to Channel 16, high power. (3) Say “MAYDAY, MAYDAY, MAYDAY.” (4) Say “THIS IS [vessel name three times, callsign/MMSI].” (5) Repeat “MAYDAY” and your vessel name once. (6) Give your position, nature of distress, number of people aboard, and assistance required. (7) End with “OVER” and release the push-to-talk button. If you forget the exact wording, still transmit: any clear call on Channel 16 is better than silence.

For routine calls, listen first, then call the other vessel on Channel 16 or 9, switch to a working channel, keep transmissions brief, and use your vessel’s name and callsign. Wait for a reply before transmitting again or changing channels. Do not use VHF for casual conversation; use a cellphone or CB radio instead.

When not to do it

VHF is not a substitute for all communication. Beyond line-of-sight range, you may need an MF/HF radiotelephone, satellite telephone, or EPIRB. For non-distress urgent situations, use PAN-PAN; for navigational safety broadcasts, use SÉCURITÉ. A cellphone is only reliable close to shore. Professional training, a human weather router, or a certified marine surveyor may be more appropriate for complex passage planning or vessel assessment. Do not rely solely on VHF for navigation or weather—cross-check with official sources. If you plan to travel more than a few miles offshore, carry an EPIRB, a second VHF or cellular telephone, and consider an MF/HF radiotelephone or satellite phone.

Visual

The following step sequence shows the correct MAYDAY voice procedure on VHF Channel 16.

1. Press and hold the red DSC distress button for 5 seconds, if fitted.
2. Switch to Channel 16 and select high power.
3. Say “MAYDAY, MAYDAY, MAYDAY.”
4. Say “THIS IS [vessel name three times, callsign/MMSI].”
5. Repeat “MAYDAY” and your vessel name once.
6. Give your position, nature of distress, number of people aboard, and assistance required.
7. End with “OVER” and release the push-to-talk button.

Common Mistakes

Transmitting without listening first

Consequence: You may interfere with an ongoing distress or safety call. Always listen on the channel before keying the microphone.

Using the wrong channel for routine calls

Consequence: You may block Channel 16, the distress channel. Use Channel 16 or 9 for initial hailing, then switch to a working channel.

Leaving the microphone open or not releasing PTT

Consequence: An open microphone blocks the channel for all other users. Maritime New Zealand identifies open microphones as the main cause of serious VHF interference.

Giving a vague position

Consequence: Rescuers cannot find you. Give latitude and longitude, or a clear range and bearing from a known landmark, and repeat it.

Not using DSC or not registering an MMSI

Consequence: You lose the automatic distress alert with your identity and position. Register your MMSI and connect your radio to GPS.

Treating VHF as a chat channel

Consequence: Unnecessary traffic clogs channels and can delay emergency communications. Marine radio is for shipping business only; use a cellphone or CB for casual conversation.

Safety Note

VHF radio is a critical safety tool, but it must fit into a broader safety framework. Digital tools and reference guides complement—never replace—proper training, physical checks, and human judgment. Always cross-check critical data such as weather, tides, and navigation with official sources like national weather services and coast guard broadcasts. Never use a tablet or phone as your only navigation tool; keep paper charts and a handheld VHF as backup. Take a certified safety and sea survival course, and practice MAYDAY procedures in a simulator or drill. Follow the International Regulations for Preventing Collisions at Sea (COLREGS) and local maritime regulations at all times. If you plan to travel more than a few miles offshore, carry an EPIRB, a second VHF or cellular telephone, and consider an MF/HF radiotelephone or satellite phone.