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VHF Radios

A VHF radio will enable you to summon help by calling the Coastguard and alerting other vessels. Up until recently this was done with a mayday call on Ch16. However, the Global Maritime Distress and Safety System (GMDSS) has changed. There is no longer a legal requirement for any ship or coast station to maintain a manual watch on Ch16. The UK Coastguard and Irish Coast Guard have ceased a dedicated Ch16 headset watch and now monitor this via a wall-mounted loudspeaker. Please check with other countries if going abroad.

Instead, commercial ships and the Coastguard now monitor a special digital channel with DSC radios. To transmit a distress message on this channel you will need a DSC radio.


Mayday call demonstration


Radio licensing

Fixed radios
Your vessel must have an up-to-date radio licence for your fixed radio. When you apply for a radio licence you will give information about your boat and the type of safety equipment onboard. Along with your licence you will be given your own unique call sign made up of a mixture of numbers and letters. Use this call sign when making a distress call and the Coastguard will be able to match it up with the details about your boat that you gave when you registered. If you have a DSC radio you will also get an MMSI number - a boat telephone number. If you don't have a licence you could face a large fine or prison sentence.

Portable / hand-held radios
Portable/hand-held radios must be licensed as well. Get this type of licence if you use your portable radio on more than one vessel.

UK licensing - OFCOM
020 7981 3000 or 0300 123 3000

Ireland licensing - MRAU
1890 443311


Operator's licence

It is a legal requirement that anyone using your radio is qualified to do so. The only exception is in an emergency situation when anyone may use the radio to call for help.

Short Range Certificate (SRC)
This type of certificate covers radio use in the GMDSS A1 sea areas. Courses and certification are administered by the RYA:
0845 345 0400

Long Range Certificate (LRC)
This type of certificate covers radio use in waters outside of the GMDSS A1 sea areas. Courses and certification are administered by AMERC:
01539 742745

Ireland licensing - MRAU
1890 443311


VHF Range

The best way to give your VHF radio increased range is to get the antenna higher. VHF radios, hand-held or fixed, once switched to maximum power, have their range limited by the height of the antenna above sea level. A small increase in antenna height, even just a metre, can give you a few more miles in range - possible vital miles in an emergency situation.

VHF radio waves cannot bend around the curve of the Earth like some other radio waves. So both the transmitting antenna and the receiving antenna need to 'see' each other. The moment one or other dips below the horizon, communication is lost.

As the diagram shows, just moving the antenna of your VHF a little bit higher means its horizon is much further away, giving your VHF radio greater range. If you are using a hand-held VHF, just standing up can double your range.

Switching to 'High' power on your radio will also increase your range but this should NOT be used unless in an emergency.


DSC radios

DSC VHF radios work just like normal VHF radios but with some added extras. They use a special channel (Channel 70) to send and receive information digitally. When you register your DSC radio with OFCOM you will get an MMSI number for the radio - your ship's telephone number.

DSC radio unit

When you talk with someone using a DSC radio, everything is exactly the same as a normal VHF radio; the difference is in how you call them up to start the conversation. Normally you hail them on Channel 16 where everyone is listening. With DSC, every DSC radio should be programmed with its own ID number called an MMSI (Maritime Mobile Service Identity).

When you want to call someone, you punch in their MMSI number into your radio along with the channel number you would like to talk on. The radio then broadcasts the number digitally on Channel 70. Only the radio of the person you are calling responds - it recognises its number, sounds an alarm and when the person you are calling presses a button accepting the call, both radios switch to the chosen talking channel and you talk as normal.

You can also send text messages to other vessels. This ability to send data comes in very useful when it comes to emergencies -see DSC digital distress (below).


DSC Digital Distress

A DSC radio can send a distress message at the touch of a button. It simply broadcasts a programmed distress text message on Channel 70 to everyone in range. This text message contains your MMSI number but can also include your position if you link your DSC radio to your GPS. The text message will set off alarms on all nearby commercial ships, at the Coastguard and on any other vessel that has a DSC radio. Sets receiving the call (and the transmitting set) re-tune to Channel 16 immediately. On most DSC radios the button that sends the distress message is large and red – normally have to lift a cover and then press and hold it for a few seconds.


VHF radio vs mobile phone

In an emergency, the most important thing is to raise the alarm but a mobile phone is a poor substitute for a radio:

  • mobile phone networks may offer poor coverage at sea
  • you can only ring one number (for example, the Coastguard); with a radio, everyone hears your call for help. There could be a vessel a mile away that hears you on the radio and could reach you in minutes
  • lifeboats and helicopters cannot home into the signal of a mobile phone - with a radio they can and will find you more quickly.