How To Use VHF In An Emergency Situation

When it comes to using a VHF, it is important to be appropriately qualified. If you find yourself in a life or death situation, however, safety of life should always take priority. You must know how to use your VHF.

The most basic operation is to set your VHF to channel 16 and then broadcast a verbal distress transmission. Channel 16 is the distress channel, which will hopefully reach the coast guard or someone else who is able to provide assistance.

What is VHF

VHF stands for Very High Frequency. In the marine environment, it describes the radio system that we use for standard and distress communications. 

It operates in the 30 to 300 MHz range, placing it in the middle of the frequency range for maritime communications.

UHF 300 – 3000 MHz

VHF 30 – 300 MHz

HF 3 – 30 MHz

MF 300 – 3000 kHz

For the purposes of this article, however, I’ll use VHF to refer to the radio equipment itself rather than the frequency range.

Types of VHF

You can split marine VHF radios into two main categories. Handheld, and fixed.

Handheld radios are self contained, with the transmitter, aerial and battery all contained within a small unit. They are lower power, and have a shorter transmission range than fixed VHFs.

Fixed VHF radios run off of a boat’s main power supply. The antenna is separate to the main unit, allowing you to mount it high up on the vessel. The extra power, and the higher antenna gives the fixed VHF a greater range than your typical hand-held radio.

Range of VHF

The range of a vhf transmission depends on both the power of the unit, and the height of the antenna.

Generally you will find that you are limited by the height of your antenna before you reach your power limit.

With a handheld unit, at the surface of the water, you can expect a range of a couple of miles. A yacht, with an antenna at the top of the mast, could achieve 20 – 30 miles. With a large ship or shore station you can transmit significantly further still. I have had situations where I have heard transmissions from over 100 miles away, although that was more to do with atmospheric conditions rather than height of the aerial alone.

The main thing to remember is that VHF is line of sight communication. If the aerials can see each other, then they should be able to communicate.

VHF Channels

VHF channels are a simple way of identifying different frequencies within the general VHF spectrum. It’s much easier to remember a channel number than it is to remember a frequency.

There are only a few channels that are internationally recognised for specific uses.

Channel 16 – Distress, safety and calling

Channel 13 – “Bridge to bridge” or safety of navigation

Channel 70 – DSC (not for voice communications)

Channel 87b & 88b – AIS

A number of other channels are reserved by national agencies in different countries. For example, in the UK, Channel 0 and Channel 67 are both used by the coastguard. In the US, Channel 9 is designated for use by recreational boaters.

Simplex or Duplex

Generally with VHF, we use simplex channels. This means that there can only be one transmission at a time.

Take Channel 16 as an example. If you broadcast anything on Channel 16, every other radio in range, set to Channel 16, will hear what you are saying. Your transmission is occupying the entire channel so no one else can use it at the same time.

Duplex, on the other hand, is like a double channel. There are two parts to it. You can think of it as “Part A” and “Part B”.

Ships will be set up to transmit on Part A, and receive on Part B. Shore stations are the opposite. They will transmit on Part B, and receive on Part A.

On a duplex channel it is possible to have a two way conversation. Both the ship and shore can transmit at the same time and receive each other’s transmission.

For basic radio operation, however, you should only need to consider simplex channels.

Making a Broadcast

Adjusting the Squelch

First off, you need to make sure your unit is turned on and the squelch is properly adjusted.

The squelch just cuts out the weaker parts of the signal. Without the squelch, there would always be a small signal that sounds like static.

To adjust the squelch, turn the volume down to minimum, then turn the squelch right down. After that, slowly increase the volume until you can hear the static clearly.

With the static loud and clear, you can slowly increase the squelch to remove the static. As soon as the static has gone, your squelch is set up right.

In a distress situation one of the things ships will do is to turn down their squelch. This is because they don’t want to reject a low powered distress signal that could be hidden within the static. A human ear will be able to make sense of it far better than the squelch control ever could.

Select a Channel

The channel for distress and calling is Channel 16. Often a radio will turn straight onto channel 16, but if it doesn’t then you’ll need to select it manually.

All radios should also have an easy button with the number 16 written on it. Pressing that is a quick and easy way to get to Channel 16 and be ready to make your broadcast. 

Push to Talk

To actually transmit, you simply hold the “PTT” button and speak clearly into the microphone.

On your unit, you will find a button labelled “PTT” which stands for “Push To Talk”. Handheld radios will probably have the button on their side. It should be marked clearly, but you can always consult your manual if you can’t find it.


“Mayday” is the international codeword for distress. When you transmit a Mayday, everyone else in the vicinity should immediately start listening and recording what you are saying.

It is important to give them all the information they need as soon as possible, ideally in your initial Mayday broadcast.

If you are transmitting your own Mayday, you start off by initiating the call to everyone else.

“Mayday, Mayday, Mayday

This is your name, your name, your name”

If you have heard someone else’s Mayday and are relaying it, you initiate the call, labelling it a “Mayday Relay” instead.

“Mayday Relay, Mayday Relay, Mayday Relay

This is your name, your name, your name”

After you have initiated the call, all stations should be listening, ready to receive the Mayday itself.

We use the mnemonic “MIPNANOO” to remember the critical bits of information.


Identity of vessel in distress

Position of vessel in distress

Nature of the distress

Assistance required

Number of persons onboard

Other relevant information


The identity within the Mayday itself is always the identity of the vessel in distress. Obviously if you have made the broadcast yourself it will match the identity in the initiation call. If you are relaying someone else’s Mayday, the identity within the initiation call is yours. A Mayday Relay still contains the identity of the vessel in distress within the Mayday itself.

Digital Selective Calling (DSC)

DSC, or digital selective calling, is a bit like a paging system for radio. Each station has an MMSI number, which is the equivalent of its phone number. You can page any individual set, or you can just page all sets in range. 

On DSC radio sets, you will have an automatic “SOS” button which will automatically page every set in range. It is usually hidden behind a cover to prevent accident transmission. Check your own set to make sure you know where it is and how to activate it.

When you activate it, probably by pressing and holding, it will send an alert to all DSC radios in range sounding an alarm on those units. It will automatically give the receivers information like your identity, and tell them a distress transmission is coming. If your radio is linked to your GPS, it should also send your position.

It does have the potential to transmit lots of other distress data as well, so you should consult your manual so that you know how to use your own unit.

After paging everyone, you then transmit the verbal distress just as we have already described.

Do you need to be Qualified to use VHF?

It depends. Around the world, different countries have different requirements.

United Kingdom

In the UK, to use a VHF you do need to have completed a course and be properly qualified.

You could do a full GMDSS course and gain your General Operator’s Certificate. This takes around 5 days to complete and costs between £1000 and £2000.

A simpler way is to obtain a Short Range Certificate. This course takes less than a day and is usually priced under £100. The Short Range Certificate is completed through the RYA in the UK.

United States

In the United States, you only need a radio license to use the radio on vessels that are legally obliged to carry a radio. This means that recreational boaters generally do not need formal qualification.

For more information about recreational VHF regulations in the US, visit the USCG site here:

In Emergencies

In a life or death situation, anyone can operate a radio. Safety of life at sea always takes priority.

More Information

Watch our video on VHF use in an emergency situation