How to Use a VHF Marine Radio

Warning: This Guide does not replace a proper VHF course–even though it offers the gist of it.

What is VHF Marine Radio?

VHF radio is a line-of-sight two-way communications system between ship-to-ship and from ship-to-shore. A very high frequency (VHF) marine radio is an essential piece of equipment on a boat when cruising beyond the bay or for navigating tricky ports. As essential as it is for safety, only nautical vessels greater than 65 feet are required to have one. Since 1920 mariners have been using a dedicated marine radio to avoid dangerous situations and to answer a SOS distress call.

For details and in-depth reviews of the best VHF Radios, read this guide.

With established frequencies for specific uses boats can communicate distress or ask about tides, currents, reefs, port conditions (including guest slips) and receive weather alerts. For this reason the most important  VHF channels to monitor or not for banter as two vessels cannot transmit at the same time. There are 4 channels dedicated to chatter not related to boat safety.

Boaters sailing through canals can also call ahead to find out the heights of bridges to avoid starring in the latest viral video of ships hitting bridges.

This compilation should serve as a warning.

In the video where the recreational boats lose a mast or get stuck inside the bridges it should serve as a reminder why skippers use marine radio to talk to bridge operators and nearby vessels.

Handheld VHF vs Fixed Mount VHF Marine Radios

There are two types of VHF units you can use, both having different characteristics and qualities.

The wide availability of VHF marine radios and the increased number of recreational sailors means there are a dizzying amount of sets to choose from with vastly different pricing. To begin with, sailors need to figure out which type of VHF is needed.

Marine radios that are fixed or portable do the same thing, but fixed sets can use an antenna atop a mast and can get more range (both transmission and reception) and generally have a more reliable power source (the boat’s).

In other words a fixed set can do much more than a handheld without fear of running low on power.

But the flipside to this last part is the batteries of a portable marine radio can get replaced or get recharged from solar panels, whereas a fixed VHF radio that runs on a boat’s power is useless if the marine battery gets pooched.

Some sailors will have both a fixed set and a cheaper portable VHF serving as backup, but others might rely on a cell phone. It’s always good to have redundancies especially considering cell coverage sucks on the water the further away from land you get.

What is a DCS?

Get a marine radio with a DCS. Most new handheld VHF radios and almost every fixed VHF set will have a digital selective calling (DSC) function. A DSC can send an automatic “mayday” call for help and can also request the position of a friend’s boat.

When a DSC button is pressed, an automatic SOS will go out to multiple channels (2, 4, 6, 8, 12 and 16) at the same time, but only if an MMSI number has been registered to the boat. A DSC signal will make rescue easier by transmitting exact coordinates to the Coast Guard and other ships within range.

Additionally, a DSC-enabled device will constantly monitor for transmissions on channel 70, receiving and cutting through any VHF channel to play a distress signal when activated by other vessels within range.

Check out this animated description of how emergency scenarios play out with a VHF radio.

Get an MMSI

Get an MMSI. Every VHF-DSC marine radio can get a unique identifier called a Maritime Mobile Service Identity number (MMSI), which is like a telephone number. The DSC function won’t send out a distress signal until an MMSI has been registered.

MMSI makes it possible for group communication on certain marine radios equipped with this feature, like the Standard Horizon HX870.

Some VHF devices have built-in GPS receivers or connect with a ship’s chartplotter in order to embed exact coordinates in case of emergency so responding ships and the coast guard will know exactly where to go. It goes without saying that crying wolf will result in a hefty fine as well as shame so only activate the mayday button if your ship is on fire or need immediate medical attention. Use channel 16 if your motor is caput and you’re stranded.

In the U.S. you can get an MMSI free of charge if you’re a member of BoatUS, Sea Tow Service International, Inc.,  or  for $25  through Shine Micro, or possibly free of charge through the United States Power Squadrons.

An MMSI is assigned free-of-charge in Canada at Industry Canada online or at one of their offices.

An MMSI is registered to a specific vessel and once entered cannot easily be changed on each model. It’s necessary to have a vessel identification number and emergency contacts when signing up. Be warned!!! After you plug-in your MMSI number you can’t change it so easily, so make sure it’s the right code.

What is an Automatic Identification System (AIS)?

An AIS displays the activity of commercial vessels within a given vicinity. This includes heading and speed relative to one’s own position and will come in handy when cruising through narrow waterways or sailing into larger ports.

Through major commercial shipping lanes an AIS is a reliable collision avoidance tool. An AIS-equipped VHF will beep a warning when another AIS-registered vessel is approaching your own position.

All ships over 300 tons are required to have AIS transmitting all sorts of info including ship speed (SOG), draft, name, course (COG), etc. These vessels fall under Class A category help prevent any mishap.

Class B AIS aren’t as expensive and are embedded in some VHF radios for recreational use. In foggy conditions these units provide an overview of every large vessel plus all vessels with AIS-equipment.

VHF Marine Antennas

What is a dB rating on an antenna? All antennas have a dB rating, which indicates how focused an antenna’s signal transmission is and what emission shape it forms. With a higher dB rating an antenna’s signal form will get more focused in more narrow bursts getting more range if transmitted from a stable platform.

Smaller boats that heel over with waves will have a higher dB signal transmission interrupted more. Even VHF antennas atop a sailboat with increased height may be better off with lower dB ratings.

It’s useful to think of this during the installation of fixed-mount VHF radios. Might as well maximize potential range.

The Radio, the Antenna & the Coaxial Cable: Keep this in Mind

Let’s assume you plan offshore cruising, where your vessel is steady and sturdy far out at sea, where land disappears for days on end. Getting a powerful fixed mount VHF radio makes sense, but without at least a 6db antenna with the thickest coaxial cable connecting it to your 25W transmitting unit, you won’t get the range you expect.

Important VHF Marine Radio Frequencies

Channel 9 and channel 16 are the most important VHF frequencies that sailors and boaters should monitor. While Channel 9 is used for important communication between vessels, Channel 16 is the SOS frequency (the international hailing and distress frequency) as well as the VHF channel over which coast guard and weather alerts will be sent.

Don’t use Channel 16 for idle chatter. Even when calling the coast guard on 16, they’ll usually request switching over to another frequency.

When approaching a marina and you don’t know what radio frequency to use to “call them”, turn to channel 68 and you’ll get in touch with someone who can tell you about guest slips and water conditions for example.

Most Import Channels

NOAA Weather Radio Frequencies

What Does SOS Stand For?

SOS is a backronym, a word that is the same backwards and forwards. In morse code 3 dots make an “S” and 3 dashes make an “O” and can be repeated quickly until someone hears the easily recognizable broadcast that everyone knows is the international call for help.

Tips for Good VHF Radio Use

• Always monitor Channel 16
• Register a MMSI
• Remember the antenna for fixed sets
• Charge your handheld and have spare batteries
• Don’t cuss over the air and use only the designated channels for chitchat
• Connect unit to GPS when possible to make DSC work

Check Your Radio

Make a radio check to ensure its working. There are now a lot of automated radio check systems set up on different channels in the United States. Simply transmit “radio check, radio check, over” on one of the designated channels and listen to how clear you sound.

In Canada you can call out on channel 9 to get a radio check then switch to one of the dedicated recreational frequencies.

Check out a demonstration

What do waterproof ratings mean?

JIS “0” No special protection

JIS “1” Vertically dripping water shall have no harmful effect (Drip resistant 1)

JIS “2” Dripping water at an angle up to 15 degrees from vertical shall have no harmful effect (Drip resistant 2)

JIS “3” Falling rain at an angle up to 60 degrees from vertical shall have no harmful effect (Rain resistant)

JIS “4” Splashing water from any direction shall have no harmful effect (Splash resistant)

JIS “5” Direct jetting water from any direction shall have no harmful effect (Jet resistant)

JIS “6” Direct jetting water from any direction shall not enter the enclosure (Water tight)

JIS “7” Water shall not enter the enclosure when it is immersed in water under defined conditions (Immersion resistant)

JIS “8” The equipment is usable for continuous submersion in water under specified pressure (Submersible)

Demonstration of a radiocheck:

Beyond radio checks there are also antenna/vhf testers that monitor signal strength of both outgoing and incoming signals.

They vary in price from $30-$250. As long as radio checks with actual people are done from time to time, the cheapest model will suffice.

To complement VHF communication, and especially useful for boaters and yachters crossing the Atlantic, internet for boats is a great asset for both weather info and to stay in contact with, well, everyone and everything. Starlink is quickly becoming the main internet on the water product for combining affordability with functionality.

Amazon Link

Then again, if radio checks over the air with automated services or with other boaters are carried out, a tester might be an unnecessary cost.

Some Marine VHF Radio Lingo

Depending on the quality of the connection between units, which is determined by the VHF models and antennas involved, it can be a bit challenging to understand each other. If you look at the nautical flag list, which has essentially an alphabet, there are flags like “whiskey” to represent “W”. Each of these also has a corresponding morse.

Head over to the nautical flags guide to learn more about this. Otherwise, here are some common VHF expressions:

• “Can I get a radiocheck, over.” 

Ask the coast guard on channel 16 to confirm signal strength and clarity of your unit. They will likely request switching to another channel like 67 or 68.

• 5-5

Second World War communications speech  indicating the strength of signal from a scale of 1-5; and the clarity of the transmission on a scale of 1-5

• Over

Break. Used to indicate the end of sentence and opening up frequency for transmission, letting other unit operators know they can respond.

• Roger

Indicates understanding. Roger that, often used to say, I get it.

• What’s your position, over

Request location.

• Over and out

End of conversation

• Pan Pan

The equivalent of sending a distress call with DSC.  Use this only when in dire straits.

If you already have a vhf marine radio or you just bought one, leave a comment in the comment section below and share your experience with it.