VHF Radios - the most common FAQs

Fixed Mount DSC VHF RadiosThe VHF radio is the most common communication system at sea. Whilst there are many thousands of radio sets in use, there is still some confusion among boat owners about the system's appropriate use. Here, we respond to some of the most frequently asked questions.

Q1 Why do you need a VHF radio if you have a mobile phone?

- VHF radio is the primary method of communication used by all rescue services at sea. It is therefore good practice to ensure that we are all using the same communication system if we ever need to call for assistance.

- A VHF radio does not have a phone number, so as long as you have your radio turned onto channel 16, you should be able to hear the rescue services trying to talk to you. You should also be able to talk back to them, without them having to find out and then dial your phone number first - or without you having to remember what their phone number is in an emergency.

- Unlike mobile phones, VHF radio does not rely on network coverage to work. With mobile phones you can easily drop out of reception when you are a mile or so offshore, even if you had a full signal when you were on shore.

- Most mobile phones are not waterproof. However, the majority of handheld VHF radios are now totally waterproof and can be left in a wet jacket pocket all day and still work in an emergency.

- A VHF radio does not just have to be used for emergencies. All harbour authorities and marinas use VHF systems to communicate to vessels. Whether it is booking a berth for a short stay, checking if the fuel pontoon is open, or for advice about where to moor up or drop anchor, using a VHF radio makes it much easier for everyone.

Q2 What range do you get out of a VHF radio?

This is one of the hardest questions to answer, but it can be broken down into several factors.

Radio travels as waves and it can be reflected or even blocked by objects such as a headland or a harbour wall. So it is true to say that VHF radio is a 'line of sight' transmission and essentially 'if you can see it, then you should be able to talk to it'

However, there are other factors:

1. Antenna

The best VHF radio on the market will still give disappointing performance with a poor quality or badly installed VHF antenna. And then there is the height of that antenna to consider.

It is the antenna that actually sends and receives the radio signals and because VHF radio is 'line of sight' then the higher the antenna, the further the range should be.

A simple guide is the following formula:

Distance (range) in nautical miles = 2.25 x Square Root of your Antenna Height

So if the antenna on a sailing boat mast 16m tall, the calculation is:

= 2.25 x √16
= 2.25 x 4
= 9 miles

However, do remember that you may also be talking to another boat with exactly the same antenna height as you. Therefore the total maximum range that you could be communicating over, will actually be 18 miles.

2. Power

Power is another influencing factor.

A strong, powerful searchlight light can be seen further and more clearly than a weak one, and the same applies to radio. Power is measured in watts and the higher the power, the further the range should be.

However, even a low power setting can give adequate range in many conditions - but power can be used to improve the quality of signal and to overcome some obstacles such as meteorological and sea conditions, or losses in the system caused by bad installation or poor quality equipment.

The disadvantage is that high power uses much more battery power and this can be problem on sailing boats with smaller battery capacities or when using handheld VHF radios with limited battery duration.

A good tip is to always start by using the low power to see if you can contact the person and talk adequately before switching to high power if range or other factors make communication difficult.

Q3 Handheld or Fixed VHF?

As with any device, there are advantages and disadvantages of both products.

Handheld VHF radios work in almost exactly the same way as their fixed-mounted equivalents, and many of the features are shared. Manufacturers often even follow the same operating protocols to help users who use both types regularly.

The Advantages of Handheld VHF Systems

Advantages of handhelds include:

  • Smaller size and portability
  • Usefulness in an emergency
  • Independence from the vessel's main power source
  • Independence from the vessel's normal antenna.

Disadvantages relate to the power output and battery life, which affect range and how long the equipment can be used.

In summary, handheld VHFs are most suitable for small vessels without their own main battery source, or for use as an emergency back-up to fixed mounted radios. They can also be useful as additional radios for crewmen to use in tenders or in dinghies.

The Advantages of Fixed VHF Systems

For vessels with battery power, a fixed mounted radio is usually the best choice. Many models are now available with waterproof fascias which allow secure installation in open boats such as RIBs, sportsboats and other day boats.

The controls are normally larger and easier to use, with a large LCD display. A fixed mounted radio also offers the benefit of a much higher maximum power output than a handheld VHF radio.

Although the basic radio functions remain the same as handheld radios, the advent of DSC (Digital Selective Calling) in fixed mounted radios has now simplified the distress calling procedure by allowing a user to press a single SOS distress button in the event of an emergency.

Q4 What is DSC? (Digital Selective Calling)

Digital Selective Calling (DSC) uses digital data, rather than voice, to transfer information between radios. This offers several key benefits:

  • Increased accuracy
  • The capability to direct the information to specific receiving radios (ie selective calling).
  • The communications range when sending digital signals is also improved.

DSC is primarily intended to initiate normal ship-to-ship and ship-to-shore VHF radio calls as well as distress alerting radio calls in emergency situations, as an alternative to trying to send a MAYDAY message by voice on VHF channel 16.

Each fixed mounted DSC type radio needs a unique MMSI Number (Maritime Mobile Service Identity) programmed into it which is issued Free of charge in the UK by OFCOM - www.ofcom.org.uk/licensing.

Using the MMSI Number

The MMSI number is normally programmed into the DSC radio by the owner using the keypad. This number acts as a digital phone number and identifies that particular DSC VHF radio. If you know the MMSI number of a friend's boat or the MMSI number of your local harbourmaster, than you can store them (and dozens more) in your VHF memory, just like a phone book.

If you then want to contact a particular vessel, simply select them from your radio's MMSI phone book, and press SEND .Your radio will send a burst of digital traffic which will 'ring' the VHF radio on that boat, sounding an alarm and informing them of the VHF channel you wish to talk to them on. Your radio will then automatically switch to the new talking channel that your radio has suggested.

DSC in an Emergency

A DSC-enabled VHF radio can also be used to send an automatic distress message when a user presses and holds the SOS distress button.

Because DSC-type radios are designed to be connected to a GPS receiver, the digital message that the radio sends will not only include your unique MMSI number but also the vessel's current position.

The digital distress message will be transmitted to all vessels in your area, as well as to the Coastguard who will be able to bring up your vessel's details and home contact numbers from the MMSI registration database.

The Coastguard will then acknowledge the digital distress message and start trying to talk to you on VHF channel 16. Your radio will have automatically switched to VHF Channel 16 once the digital distress message has been sent. If the Coastguard does not acknowledge your first distress message, the radio will keep automatically sending another distress message every four minutes until they respond.

The distress message menu on a DSC type radio will allow you to send various types of 'header' or title to your distress message including FIRE, SINKING, COLLISION, MAN OVERBOARD and several others. This way the Coastguard will be able to understand the nature of the distress even before they have been able to start talking to you.

Q5 What is GMDSS and does it apply to my vessel?

The Global Maritime Distress and Safety System (GMDSS) is a maritime communications system - not just for emergency and distress messages, but also for all types of existing ship-to-ship and ship-to-shore routine communications.

It was originally conceived for the commercial shipping sector and commercial vessels over 300 tons, and some smaller commercial vessels, including some fishing boats, must fit GMDSS equipment by law.

There are several elements that make up the total GMDSS system. These include

  • Digital Selective Calling (DSC) via VHF radio (as well as HF Radio and Satcoms)
  • Navtex-based weather reports and navigational information
  • Search and rescue equipment such as Radar Transponders (SARTs) and Emergency Position Indicating Radio Beacons (EPIRBs).

All this equipment goes together to provide a comprehensive communications system between vessels and the shore, for the receipt of important weather and navigational information, and to allow distress signals to be sent quickly and efficiently by a dedicated means.

Whilst it is only voluntary for leisure craft to fit any of this equipment, the Coastguard strongly recommends that all leisure vessels upgrade to Digital Selective Calling (DSC) VHF radios as soon as possible, as this is now the primary method used to manage distress calls throughout the UK and across Europe.

Q6 Is it true that the Coastguard no longer listens to Channel 16 for mayday calls?

This is not quite true.

HM Coastguard has traditionally kept what was called a 'headset listening watch' on VHF Channel 16. This meant that a Coastguard Watch Officer was specifically tasked with monitoring this channel for any vessels broadcasting a MAYDAY or other urgent message.

This was very labour intensive and meant that the Coastguard Officer could not effectively handle other routine tasks at the same time.

With the introduction of DSC radio equipment in the commercial sector, and the subsequent availability of cost-effective DSC radio equipment in the leisure sector, the Coastguard announced that from February 2005, they would no longer keep a dedicated 'headset listening watch' on Channel 16, but they would move over to a 'speaker-based listening watch'.

So in fact HM Coastguard has said they are going to maintain a revised Channel 16 listening watch for the foreseeable future. However, boat owners must understand that outside UK waters, foreign coastguards may not be listening on Channel 16 and they may require you to contact them by DSC initially.

Peter Dymond, Head of Search and Rescue at HM Coastguard commented:

"Due to the increasing range of communications methods available to the mariner and the other tasks now undertaken by Coastguard Rescue Co-ordination Centre staff, a different approach to managing an operations room was required. However, our Operations Room Managers can still undertake a 'headset' listening watch on VHF Channel 16 if the risk, current operations, room noise levels or other circumstances demand it".

"Our state-of-the-art Integrated Coastguard Communications System (ICCS) also provides an instant playback facility for VHF Channel 16 and the other VHF channels being monitored. Despite these changes, HM Coastguard will continue to be responsible for the integrity of VHF Channel 16. This means ensuring that VHF Channel 16 should only be used for the establishment of normal voice communications which should then be quickly transferred to a suitable working channel, and for distress, urgency and brief safety communications. This includes the announcement of maritime safety information broadcasts."

"We also continue to recommend the installation of effective, suitable radio communications equipment on all leisure vessels and would remind all seafarers that mobile phones cannot be totally relied upon when at sea for distress and other emergency calls".

Q7 Do I need a VHF License, and how much does one cost?

All marine VHF radios require both the user and the vessel to hold a relevant license.

The vessel's license is much like the tax disc on a car and licenses the boat to carry a radio transmitter. It is also the way to obtain an MMSI number for a DSC VHF radio. This license is issued FREE of charge by OFCOM and can be applied for on-line at the OFCOM web site, www.ofcom.org.uk/licensing

The user will also require a radio operator's license, which is similar to a driving license and proves that you have been properly trained in using a VHF radio.

For VHF only, the SRC (Short Range Certificate) is available. Training takes just one day and this instructs users in radio etiquette and procedures, since VHF operation itself is relatively straightforward.

For other communications such as HF Radio and Satcoms, the LRC (Long Range Certificate) is required.

VHF radio training courses are available nationwide and are usually run by RYA (Royal Yachting Association) approved sailing schools and at night school classes run by RYA instructors.

Information about RYA-approved VHF radio training courses in your area can be found on the RYA website.

To see the range of VHF handheld and fixed DSC radios now available, click here or for further technical advice, contact the Safety Marine technical team on advice@safety-marine.co.uk or call +44 (0)2380 226300


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