VHF Marine Radio: An Overview

Marine Radio

VHF Marine Radio--Important Safety Equipment

A VHF marine radio may be the most important piece of safety equipment on a recreational boat. Countless lives have been saved due to a properly functioning radio, and someone who knew how to use it.

Yet, unless you're an experienced boater, you may not be familiar at all with marine radio. My purpose here is to give an overview of what marine VHF radio is, what it can do, and how to use it.

What is VHF Marine Radio?

Radio is divided into radio services—marine radio service, citizens band radio service, amateur radio service, family radio service, general mobile radio service, and so on. The marine radio service is reserved for boaters.

Radio waves occur with varying frequency. The range of radio-wave frequencies is called the radio spectrum. The radio spectrum includes waves of different frequencies—low, medium, high, very high, and ultra high. Very-high-frequency marine radio, or VHF marine radio refers then to that part of the marine radio service that transmits and receives on the VHF frequencies.

The Radio Spectrum

Some frequencies in the radio spectrum other than VHF also belong to marine radio. These are the high-frequency (HF) signals of single side-band radio. Single side-band is often used by those venturing out more than about 25 nautical miles off shore because it has a much longer range than the popular VHF radio used for more near-shore cruising. The subject of single-side band is interesting, but beyond our scope here.

VHF Waves are Line of Sight

Radio waves behave differently, depending on their frequency. For example, VHF radio waves tend to travel in a straight line, and won't normally bend around the earth's curvature, as will HF waves.

VHF radio waves are line of sight

Since they don't typically bend, VHF waves are described as line of sight. This means both the sending and the receiving antennas must “see” each other above the horizon. The top of either antenna must not be under the horizon.

What is the Range of VHF Radio?

As you can imagine, the line-of-sight feature of VHF waves limits the useful distance of VHF radio. Depending on heights of the sending and receiving antennas, the useful distance of surface-based (as opposed to aircraft-based) VHF radio extends to about 25 nautical miles.

An important principle: the higher the sending and receiving antennas, the greater the useful distance.

Two hand-held VHF marine radios, for example, each only a few feet above the water, might be able to talk to each other over a distance of only four or five nautical miles. But two sailboats, each with each with a high, mast-mounted antenna might be able to communicate with each other over VHF marine radio maybe 15 nautical miles. In perhaps a best-case scenario, a VHF marine radio with an antenna atop a 60-foot mast might be able to communicate with an onshore radio using a 250-foot-high antenna, over 25 nautical miles or so.

vhf - The higher the antennas the greater the range

VHF Radio Licensing and Usage

Recreational users of marine VHF radio need not be licensed, providing their vessel is not over 20 meters in length, and they do not travel to foreign ports or transmit to foreign stations. (A station in radio speak means a working radio.)

If you’re not required to have a license, you’re not required to have a radio on your boat. For safety’s sake, however, have a radio anyway. If you have a radio, you must keep it turned on and guard (radio speak for “listen to”) Channel 16 when you’re underway and not talking on another channel.

Cell Phones are no Substitute

By all means, carry a cell phone on your boat. But don’t figure it substitutes for a VHF marine radio. Having a marine radio tuned to Channel 16 makes you part of the “boating network.” You’ll hear important radio traffic such as Coast Guard safety messages to be announced on Channel 22A, and weather updates. Plus, you’ll hear the radio traffic of other boats in your area, maybe even a nearby distress call.

Stormy sunrise over the Atlantic Ocean

Stormy sunrise over the Atlantic Ocean

Should you have to issue a distress call, your message instantly goes out not only to the Coast Guard, but also to all boats in the area with a VHF marine radio. Lifesaving help may come quickly from a nearby fellow boater. What’s more, if you don’t know where you are, the Coast Guard can often pinpoint your position from your radio signals. As far as I know, the Coast Guard cannot locate the position of a cell-phone caller. If the cell-phone call is dropped, the Coast Guard may not be able to re-establish contact with you.

The range of a marine radio is usually greater than that of a cell phone. And marine radios tend to be more rugged and water resistant than most cell phones.

Marine Radio Frequencies and Channels

The Federal Government regulates the airwaves, allowing certain types of users to use certain specified frequencies. Boaters, for example, are allotted about 51 specific frequencies for their communications needs. Each separate frequency can be referred to by its designated channel number. For example, 156.8 megahertz, is normally just called Channel 16.

Each channel is reserved for certain specified uses.

Further, the specified uses for each channel can depend on location. In the Great Lakes region, for example, recreational boaters must use Channel 9 instead of Channel 16 as a hailing channel. (In marine radio lingo, to “hail” means to call for the purpose of establishing contact.)

Let's look at the channels often used by recreational boaters:

16 156.800 MHz Reserved for distress, safety, and calling. You could, for example, use Channel 16 to call a marina, or another boat. Once you make contact, you must shift to a "working" channel to continue your conversation. Shifting to a working channel once you’ve successfully hailed your party avoids needlessly tying up the all-important Channel 16.
9 156.450 MHz Boater calling channel for both commercial and non-commercial purposes. Here in Florida, this channel is used to talk with bridge tenders.
22A 157.100 MHz This is the U.S. Coast Guard's liaison channel with the public. Used for safety broadcasts. The fact that such broadcasts are about to take place is announced first on Channel 16, and boaters are advised to shift to Channel 22A to hear the broadcast.
68 156.425 MHz Non-commercialworking channel
69 156.475 MHz Non-commercialworking channel
70 156.525 MHz Used forDigital Selective Calling (DSC). This is a data-only channel, and no voice communications are allowed.
72 156.625 MHz For intership use.

Nature of a Radio Conversation

Unlike telephone conversations, radio communications are not private. When you transmit over the vhf marine radio, the whole world could be listening. Even though you’re talking to only one person, your conversation is available over the airwaves to anyone within range tuned to your frequency. Your communications, therefore, must maintain a different decorum than a totally private conversation.

Marine Radio Has its Own Way of Talking

United States Coast Guard Auxiliary

There are customary manners or rules for talking on marine radio. Considering the non-private nature of marine radio communications, no profanity is allowed. Assuming, of course, the local language is English, the use of plain English—in lieu of 10-codes, for example—is encouraged.


Within marine radio is a list of procedure words. These pro-words, as they are called, are simply customary expressions used in specific instances for uniformity, clarity and brevity.

Some examples of common pro-words and their widely understood meanings are:

OVER This is the end of my transmission. I expect a reply
ROGER I have received your transmission satisfactorily.
WILCO I havereceived your message. I understand, and I will comply.
SAY AGAIN Repeat. (The word "repeat" historically on VHF radio has to do with calling in repeat artillery fire, and is therefore avoided except in that context.)
I SAY AGAIN I am repeating
I SPELL I shall spell the word phonetically, using the phonetic alphabet.
WAIT I must pause for a few seconds
WAIT OUT I must pause longer than a few seconds.
THIS IS Used to identify yourself when calling.
FIGURES Numerals or numbers follow
MAYDAY I am in distress (imminent life-threatening danger. This word is the marine radio equivalent of dialing 9-1-1.

Use the Phonetic Alphabet

Further, to reduce confusion when saying on the air any letter of the alphabet, use the phonetic alphabet name for the letter, as follows:



Regarding saying numerals on the air, just say them carefully and distinctly. The only numeral that’s significantly different is nine, which is pronounced nine-er. Always call a zero a zero, never an “OH.”

Transmit numerals individually, as follows in these examples:

16 Say one-six, NOT sixteen. For instance,Channel one-six.
45 Say four-five, NOT forty five.
173 Sayone-seven-three, NOTone-hundred-and-seventy-three.
500 Say five hundred
1520 Say one-five-two-zero.
18,000 Say one-eight thousand
152,000 Say one-five-two thousand

Nobody’s going to hang you from the yardarm if your radio speak isn’t perfect (as long as you’re not cursing, and I’m not sure what the penalty for that is), but do your best to get it right. Proper radio speak reflects well on you.

Many non-boaters may think all the rogers, overs, and nine-ers of radio speak sound too Hollywood, but there's good reason for standard radio talk. Uniformity makes communications more understandable, and keeps messages short and to the point. Brevity helps ensure crowded channels will be available to all boaters when needed.

Each radio service seems to have its own culture, its own way of talking. Marine radio has its speech distinctions, as does CB radio. Well-known CB phrases such as Got your ears on?, Come back, ten-four, and so on are out of place on marine radio.

Example of a Routine Call

Let’s say you’re on the vessel King Fisher, and you want to hail the Shady Lady, and request they talk with you on Channel 68. The exchange of transmissions between you and the Shady Lady should sound something like this (pro-words are in all caps and your words are in bold):

Shady Lady. Shady Lady. Shady Lady. THIS IS the King Fisher. OVER.
You stated the called boat's name three times to give the radio watchstander time to respond. Then, you announced who you are, said OVER, and awaited a reply.
King Fisher. THIS IS the Shady Lady. OVER. Shady Lady responded to you by addressing you, then identifying itself, said OVER, and awaited your reply.
Shady Lady. THIS IS the King Fisher. Shift to Channel six-eight. OVER. You re-addressed the party you're talking to, and re-identified yourself. Always do these things each time you talk. Then you requested the Shady Lady switch to a working channel--in this case channel six-eight.You then said OVER, and awaited a reply. 
King Fisher. THIS IS Shady Lady. Roger. Wilco. Out. Shady Lady followed good radio procedure by re-addressing you and re-identifying itself. Shady Lady then acknowledged your transmission, agreed to comply, and ended theconversation on Channel 16.

Now that Shady Lady’s been hailed, let’s go to Channel 68 for our conversation:

Shady Lady. THIS IS the KingFisher. OVER.
King Fisher. THIS IS Shady Lady. OVER.
Shady Lady. King Fisher. Are you catching any groupers over there on the reef?
King Fisher. Shady Lady. No. And even if we were, we wouldn't say.
Shady Lady. THIS IS King Fisher. ROGER. OUT.

That’s the end of the conversation. Once someone says OUT, there’s no need to respond. OUT means “I’m gone.”

Rescue 21

Marine Radio DSC Distress Button

Recently, the U.S. Coast Guard has upgraded its ability to receive and respond to distress calls. The new, upgraded response system is called Rescue 21. It now covers all Florida coastlines, and most of the entire U.S. coastline. Rescue 21 provides stronger radio signals, and can receive VHF transmissions from about 25 nautical miles. Plus Rescue 21 can record a voice distress call for immediate playback, and offers enhanced radio direction finding capabilities for pinpointing the position of distressed vessels. Rescue 21 also takes advantage of Digital Selective Calling (DSC), an enhanced hailing system that can send in about one-third of a second an information-laden digital distress signal, in lieu of a voice MAYDAY call.

Making Distress Calls

For marine radio purposes, distress means an imminent threat to life or limb. If your situation involves such a threat, issue a distress call. With a newer VHF marine radio equipped with Digital Selective Calling (DSC), you can do this digitally, or by voice. With an older radio, not so equipped, a voice call is your only option.

Digital Distress Calls

A newer marine radio equipped with DSC allows you to issue a distress call by pushing a single button. This panic button is protected by a hinged cover so you can’t depress it by accident.

When you push this button, a digital data transmission goes out over Channel 70 to all VHF/DSC radios within range. The VHF/DSC radios of boaters who receive your DSC transmission will sound off to advise them of your distress. The data transmitted by your DSC distress call is then stored in each boat’s radio. Your distress transmission will continue to go out until acknowledged by a shore-based Coast Guard station.

If no shore-based Coast Guard station is within range, the DSC distress transmission will “hop” from one DSC/VHF-equipped radio to another until it finds a shore-based station that returns an acknowledgement of your distress. By hopping from one DSC/VHF radio to another, your distress signal can travel long distances, since each radio in the hop sequence repeats the signal.

To illustrate, we’ll say you’re 40 nautical miles off shore and issue a DSC distress signal. As you know by now, 40 nautical miles is probably out of VHF range. But the nearest DSC/VHF-equipped boat to you (we’ll call it Boat 1) is only seven miles away. Boat 1’s radio picks up your distress signal, stores your information, and automatically sends your signal on to another DSC/VHF-equipped boat (Boat 2) 10 miles down the line. Boat 2’s radio picks up your signal, stores its information, and automatically sends the signal to Boat 3 a few miles farther down the line. Boat 3’s DSC/VHF-equipped radio receives your signal, stores its information, and automatically sends the signal to a shore-based Coast Guard station within range. All this receiving and sending down the line takes place in a flash. The shore-based Coast Guard station acknowledges the signal. That acknowledgement then hops lightning fast back to you through the chain of DSC/VHF-equipped boats.

Your DSC distress call provides rescuers with essential data, including your name, emergency contact information, a description of your vessel, and your latitude and longitude. This data comes from two sources: 1) your MMSI number, and 2) your GPS. Moreover, when you send the call you can designate by a menu of choices the nature of your distress. Or, the nature of distress may be left undesignated.

MMSI stands for Mobile Maritime Service Identity. Your MMSI--a vital part of DSC—is a nine-digit number assigned to your boat—not to your radio, to your boat. All radios on the same boat will use the same MMSI. Without an MMSI stored in a radio, that radio can’t use DSC.

If you’re going to boat only in U.S. waters, you can get an MMSI by applying online at http://www.boatus.com/mmsi . If you plan to travel outside the U.S., get your MMSI when you get your VHF license with the FCC.

Upon applying for an MMSI, you will supply your name, contact information, and vessel description. When you receive your MMSI, input it into your radio. When the Coast Guard receives a VHF/DSC distress call from your radio, your MMSI information—name, vessel description, and contact info—is then available to them.

Your latitude and longitude is included in your DSC distress transmission if your radio is hooked up to a working GPS.

Besides making distress calls, DSC can also be used for ordinary hailing, relieving Channel 16 of traffic. To call another boat, input its MMSI into your radio, the channel you want to talk on, and send a DSC non-emergency signal. In less than a second, the other boat’s radio will get the message you want to talk, and will automatically be switched to the working channel specified by you in your DSC call. You and the other party can now talk without ever having to initiate a voice conversation on Channel 16.

Voice Distress Calls

You can make the traditional voice MAYDAY call on Channel 16. MAYDAY is the pro-word for distress. Saying MAYDAY on the radio is like dialing 9-1-1. Don’t do it, unless there’s a good reason.

To make a MAYDAY call, first be sure:

You’re radio is on.
You’re on Channel 16.
The radio’s volume is turned up.
The squelch control is adjusted.
You’re transmitting on HI power, not LO.

Press the push-to-talk button on the microphone, then say:

2. THIS IS say your vessel’s name three times.
3. MAYDAY. THIS IS say your vessel’s name once.
4. Our position is say your lat/long position, or some other indicator of position.
5. Say the nature of your distress (fire, collision, sinking, capsizing, explosion, man overboard, piracy, grounding, …whatever).
6. Say what kind of help you need (medical, pump, whatever).
7. Say the number of persons on board (POBs) and the condition of any injured.
8. Describe your vessel and its seaworthiness.

Example of a MAYDAY call:

2. THIS IS the Seagull. Seagull. Seagull.
3. MAYDAY. THIS IS the Seagull.
4. Our position is 29 degrees, 55 decimal 7 minutes North; 081 degrees, 12 decimal 7 minutes West. (In radio speak, say “day-cee-mahl” instead of “point” or “dot.”) About 4 nautical miles east of the St. Augustine inlet.
5. Our boat is on fire.
6. We need immediate lifesaving assistance.
7. We have 4 persons on board, all wearing life jackets, one with second-degree burns on most of his left leg.
8. The Seagull is a 32’ white trawler with a black hull. We have to get off this boat now. We are deploying the life raft.

MAYDAY calls aren’t hard to make, but a boating newby may not have a clue as to how to do it. That’s the beauty of DSC. If that newby just knows to lift the hinged cover and push the DSC panic button, that’s all it takes.

If you hear a MAYDAY call.

As a boater, you are expected to help other vessels in distress, as long as you can safely do so. If you hear a MAYDAY call, write down the information, and the exact time. For this purpose, keep a pencil and notebook near the radio. Maintain radio silence while giving the Coast Guard time to answer. If the Coast Guard doesn’t answer promptly, answer the vessel in distress, as follows:

1. MAYDAY. Say three times the name of the vessel in distress.
2. THIS IS Say your vessel’s name three times. 3. Received MAYDAY.

Let’s say you heard the MAYDAY call above. A minute or two has passed, and the Coast Guard has not answered. You answer, as follows:

1. MAYDAY. Seagull. Seagull. Seagull.
2. THIS IS the King Fisher. King Fisher. King Fisher.
3. Received MAYDAY.


The vessel in distress may be out of the Coast Guard’s radio range. Yet, you may be somewhere between the vessel in distress and the Coast Guard, and able to talk to and hear both. Just as the DSC distress call in the example above hopped automatically from boat to boat, you can when necessary let a MAYDAY call “hop” through you by sending a voice call known as a MAYDAY RELAY down the line over Channel 16, as follows:

2. THIS IS give your vessel’s name three times.
3. This is your vessel’s name with a MAYDAY RELAY.
4. Give the Coast Guard the information you have regarding the vessel in distress.

2. This is the King Fisher. King Fisher. King Fisher.
3. This is the King Fisher with a MAYDAY RELAY.
4. The Seagull is on fire. Her position is 29 degrees, 55 decimal 7 minutes North; 081 degrees, 12 decimal 7 minutes West. Four persons aboard, all wearing life jackets, one with second-degree leg burns. The Seagull is a 32-foot white trawler with a black hull. The Seagull’s Captain stated two minutes ago they are deploying their life raft.

The MAYDAY information you wrote down when the Seagull’s distress call came in, may turn out to be vitally important in saving the lives of its Captain and crew. Do your dead-level best to record the information legibly and accurately.

For more information on marine radio, I highly recommend you watch BoatUS's 38 minute video tutorial on VHF marine radio. It's called "Can You Hear Me?"

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