Marine VHF is much more than just a means of communication on board: it is a vital safety device that can save lives at sea. However, many boaters navigate with a poorly configured VHF, sometimes unaware that their device could not transmit their position in an emergency. Misconfiguration can turn this valuable tool into a dangerous false security. Without a properly programmed MMSI number or without a functioning GPS connection, your emergency call may never reach the emergency services with the information you need to locate you. This guide is for all mariners, whether they are involved in occasional coastal navigation or preparing for offshore crossings. You will discover how to methodically configure your VHF so that it fully fulfills its safety mission, from pre-checks to advanced settings, including best practices for use and maintenance.
Understanding the role of VHF in maritime safety
What is the purpose of a marine VHF?
Marine VHF is the standard communication system at sea, allowing above all to transmit distress, emergency and safety messages. When a navigator is in trouble, VHF allows him to emit an alert signal that will be picked up by nearby coastal stations and ships, thus triggering the maritime rescue chain. Beyond emergency situations, this equipment facilitates daily exchanges with other ships to coordinate maneuvers, avoid collisions or share weather information. Communications with maritime authorities, ports and locks also pass through this privileged channel.
The distinction between portable VHF and fixed VHF deserves attention. The fixed VHF, permanently installed on the boat, has a transmission power of twenty-five watts and an antenna positioned at a height, offering a range of up to forty kilometers under favorable conditions. Portable VHF, with its power limited to one watt in general, is more of an emergency or auxiliary equipment, its range rarely exceeding five kilometers. This difference in performance directly influences the ability to communicate effectively in critical situations.
VHF, ASN and safety: what you need to know
ASN, or Digital Selective Calling, also known by the English acronym DSC (Digital Selective Calling), represents a major evolution in maritime safety. This system automatically sends a digital distress message containing your identity and GPS location to nearby coastal stations and equipped vessels. Unlike a voice call on channel sixteen, the ASN alert is instant, silent and does not require complex manipulations under stress.
ASN has become indispensable today because it is integrated into the Global Maritime Distress and Safety System. The Regional Operational Centers for Surveillance and Rescue constantly monitor channel seventy reserved for ASN calls and can immediately locate a boat in distress thanks to the data transmitted. This technology significantly reduces emergency response times.
Regulatory requirements vary depending on your area of navigation. For navigation in division 240, which corresponds to navigation within six miles of a shelter, VHF is not mandatory but strongly recommended. In division 245, up to two miles from a shelter, a VHF becomes mandatory. For divisions 200 to 245, a VHF with ASN is required, and the MMSI must be properly programmed. Offshore mariners must also have a radio operator's license (CRR or restricted radio operator certificate).
Essential checks before setting up your VHF
Choosing a VHF adapted to your boat and its navigation
Transmission power is the first criterion for selecting a marine VHF. Portable models generally emit between one and six watts, while fixed VHFs offer a maximum power of twenty-five watts. For main use on board a boat, always choose a fixed VHF that makes full use of the twenty-five authorized watts, guaranteeing an optimal range. The possibility of reducing the power to one watt is still useful for short distance communications, thus saving energy and avoiding channel saturation.
Watertightness and robustness are essential characteristics in the marine environment. Look for IPX7 or IPX8 certified devices that can withstand temporary submersion. The housing must withstand splashes of salt water, ultraviolet light and shocks associated with boat movements. The connectors should be protected and the buttons easy to handle even with wet hands or gloves.
ASN and GPS compatibility is now an essential standard. Make sure that the VHF has a built-in GPS receiver or that it can connect to your on-board GPS. Some high-end models even incorporate an internal GPS receiver to ensure position transmission even in the event of a failure of the main GPS. Solutions like the Oria Marine IoT box can also facilitate the integration and centralization of navigation data, including position information essential for safety.
Verify the installation on board
The power supply of your fixed VHF must be directly connected to the service battery by a dedicated circuit, protected by a fuse adapted to the consumption of the device. Check that the connections are clean, tight, and protected against corrosion. Poor contact can cause untimely cuts or a drop in transmission power. The fuse should match the manufacturer's specifications, generally between two and ten amps depending on the model.
The quality of the antenna and the coaxial cable directly determines the performance of your VHF. A poor quality or poorly adapted antenna can reduce the range by half or more. The coaxial cable must have an impedance of fifty ohms and minimum losses, especially if the length exceeds six meters. Avoid tight bends when routing the cable and check the insulation jacket for damage. The connections at both ends must be perfectly watertight to prevent moisture from entering, which would progressively degrade performance.
The optimal positioning of the VHF and the antenna significantly influences the effectiveness of communications. The VHF console must be installed in a location that is easily accessible from the steering position, allowing quick use in all circumstances. The antenna should be mounted at the highest possible point on the boat, free of any metallic obstacles that would create interference. On a sailboat, choose the top of the back balcony rather than the masthead, because the roll and roll movements are less pronounced there. Maintain a minimum distance of one meter from other antennas to avoid parasitic interactions.
Setting up your VHF correctly for security
Program the MMSI number
The MMSI, or Maritime Mobile Service Identity, represents your unique identity on maritime waves. This nine-digit number works like a maritime telephone number, allowing you to precisely identify your ship during any communication, and particularly during an ASN distress call. When you press the distress button, the MMSI is automatically transmitted with your location, allowing emergency services to immediately know who you are and to consult the information on your boat.
Obtaining the MMSI is done free of charge from the Agence Nationale des Fréquences for ships flying the French flag. The request is made online via the ANFR website, by providing information on your vessel and your contact details. The number is issued within a few days and remains attached to the boat, not to the owner. For European sailors with a foreign flag, the award is made to the competent authority of the country of registration.
The procedure for entering the MMSI on your VHF requires special attention as this operation can usually only be done once. Consult your device manual carefully as the method varies between manufacturers. Most VHFs require access to a specific menu the first time you switch on. Enter all nine digits with extreme caution, verifying each entry. An error would make your ASN system inoperable or worse, could trigger an alert for another ship. Some models require you to keep several buttons pressed simultaneously during ignition to access programming mode. Never attempt to force reprogramming without following the official procedure, as this may damage the device's memory.
Connect the VHF to the GPS
The advantage of connecting your VHF to the GPS lies in the automatic transmission of your position during a distress alert. Without this connection, the ASN alert will be issued with your identity but without geographic coordinates, forcing emergency services to locate your radio signal, which takes precious time. With connected GPS, your exact location appears instantly on the screens of monitoring stations, considerably speeding up the intervention.
The types of connections between VHF and GPS generally follow two standard protocols. The NMEA 0183 is the oldest but still widely used system, using a serial connection with separate wires to transmit and receive data. This standard works unidirectionally, with GPS simply sending its position information to the VHF. The more recent NMEA 2000 uses a bi-directional data bus allowing the exchange of information between all the electronic equipment on board. This technology facilitates installation and allows advanced features such as automatic time updates.
The correct functioning is checked directly on the screen of your VHF. A symbol representing a GPS antenna or a position indicator should appear when the connection is established and the GPS has acquired the satellites. Access your VHF menu to view the GPS coordinates received, then compare them with those shown on your GPS or tracker. The values should be the same within a few arcseconds. Also, test that the position is updated regularly while browsing, confirming that the data flow is continuous and stable.
Adjust channels and key functions
Channel Sixteen is the international channel for distress, emergency and maritime VHF calls. Your VHF must be kept on constant watch on this channel when you are sailing, because it is through this that voice alerts are broadcast and that the first exchanges with the emergency services are established. After an initial call on Sixteen, communications must quickly switch to a working channel to release this vital frequency. Never use channel sixteen for ordinary conversations, this practice is not only forbidden but can mask a distress call.
Safety and traffic channels deserve to be set to your favorites for quick access. Channel seventy remains exclusively reserved for ASN calls and should never be used for voice communications. Your VHF automatically monitors this channel at all times. Channel six is used for communications between ships to coordinate maneuvers and avoid collisions. Channels seventy-two and seventy-seven are used for intership communications, while local channels vary by region for communications with ports, locks, or marine traffic services.
Setting the Squelch, or Mute, allows background noise to be filtered out when no signal is received. Turn the Squelch Knob gradually until the white noise disappears, then go back slightly. Setting too high may block weak signals, while setting too low will tire you out with a constant crackle. The volume should be high enough to hear communications clearly even with the ambient noise of the boat, wind, and sea.
Activating dual standby, called Dual Watch or Tri Watch depending on the model, allows your VHF to simultaneously monitor channel sixteen and another channel of your choice. This function is particularly useful when you listen to a weather channel or a port channel while remaining attentive to distress calls. The VHF automatically switches to channel sixteen as soon as a call starts there. Some devices even offer triple standby including channel seventy ASN, channel sixteen, and an additional channel.
Set up and test distress functions
Understanding the Distress button
The red distress button, generally protected by a hood or requiring prolonged pressure, triggers the sending of an ASN alert on channel seventy. This alert contains your MMSI, GPS location, time, and nature of the distress. Pressing this button should be reserved for situations where human life is in immediate danger: major waterway, fire, man overboard with no possibility of recovery, serious medical emergency. The system then automatically switches the VHF to channel sixteen to allow voice communication to be established with emergency services.
The types of ASN alerts come in several priority levels. The Mayday alert, triggered by the distress button, signals a serious and imminent danger requiring immediate assistance. The Pan-Pan alert corresponds to an emergency situation concerning the safety of the ship or of a person on board, with no immediate danger of loss of life. The Safety Alert, announced with the term Safety repeated three times, transmits important information concerning navigation or weather. Some VHFs allow you to select the type of alert before emission, but when in doubt, always choose the higher level.
When using the distress button, press and hold it for several seconds until the alert is confirmed visually and audibly. The VHF will automatically repeat the ASN alert every few minutes until an acknowledgement of receipt is received. Then get ready to communicate vocally on channel sixteen by providing details about your situation, the number of people on board, and the assistance needed. Keep your VHF on even if you have to abandon ship, the continuous emissions will help locate you.
Test your VHF without triggering a false alarm
Authorized ASN tests are carried out only in coordination with maritime authorities or according to strictly supervised procedures. Never test your system by actually pressing the distress button outside of a supervised exercise. CROSS regularly organize maritime safety exercises where you can participate and test your equipment under controlled conditions. Some VHFs offer an internal test mode that simulates sending an alert without actually transmitting on the airwaves.
Recommended procedures for verifying the proper functioning of your VHF include regular emission tests with other vessels or test stations. Ask another equipped navigator to check the quality of your signal and the clarity of your voice. Check that the GPS display on your VHF corresponds to your real position. Also, verify that the standby on channel sixteen and channel seventy ASN is working properly by listening to surrounding communications.
The frequency of checks should be monthly for a regular browser, and systematic before each trip for those who browse occasionally. Take advantage of wintering to have your installation revised by a professional who will check the condition of the antenna, cable, connections and perform accurate emission power measurements. Neglected safety equipment can give you dangerous false confidence the day you really need it.
Best practices for optimal security
The rules of radio communication at sea
Radio messages at sea follow standardized formats that make it easy to understand even under difficult conditions. Always start by identifying the recipient of your call by repeating their name or area code three times, then identify yourself in the same way. Speak slowly, clearly, articulating each word. Use the international phonetic alphabet to spell important names or numbers: Alpha, Bravo, Charlie, Delta, and so on. End each transmission with the word “Done” to indicate that you are waiting for a response, or “Done, end” to end the communication once and for all.
Security communications are prioritized in a strict order that all browsers must follow. Mayday distress calls have top priority, all other users should immediately stop transmitting and listen. Pan-Pan emergency messages come next, followed by safety messages preceded by the word Safety. Ordinary communications should never interfere with these three categories. If you are on normal communication and a distress call starts, stop your conversation immediately.
Common mistakes to avoid include chatting for a long time on work channels, using channel sixteen for regular conversations, or broadcasting without ensuring that the frequency is free. Never test your VHF by making fictitious distress calls. Also, avoid monopolizing a channel during periods of high traffic. Always speak while keeping the microphone a few inches away from your mouth, not too close to avoid saturation, and not too far away to ensure good intelligibility. Only press the broadcast button after you have mentally prepared your message.
Regular maintenance and checks of the VHF
Periodic checks on your VHF include simple but essential visual and functional checks. Regularly check the condition of the case, buttons, and screen for signs of water ingress or corrosion. Check that the seals remain soft and in good condition. Test that all buttons respond correctly and that the settings are maintained after switching off. Check the battery charge for portable VHF and replace it as soon as the battery life decreases significantly.
Protection against humidity and salt requires constant attention in the marine environment. Rinse your VHF outdoor console regularly with fresh water to remove salt deposits. Apply a protective spray suitable for electronic equipment to connectors and exposed metal parts. For portable VHFs, always use a waterproof case when storing and check that the battery compartment seals are clean and properly positioned. Store your portable equipment in a dry, ventilated area when not on board.
The updating and replacement of equipment take place according to technological evolution and the condition of your equipment. Manufacturers sometimes offer software updates for their recent VHFs, improving features or correcting faults. Check their website regularly. Replace your VHF if it does not have an ASN function, as this technology has become an essential safety standard. An antenna that shows traces of corrosion at its base, cracks in its plastic protection or that has suffered a violent shock must be changed without delay. Coaxial cable gradually degrades with humidity and ultraviolet light, consider replacing it every five to ten years depending on exposure.
Common mistakes to avoid when setting up a VHF
Incorrectly entered or absent MMSI represents the most critical error and unfortunately all too frequent. Many boaters sail with a VHF ASN whose MMSI has never been programmed, making the system completely ineffective in case of emergency. The distress alert would be issued but without identification, considerably complicating the work of the emergency services. An error in entering a single number in the MMSI can have serious consequences, as your alert is attributed to another ship. Take the time to check and double-check each number during initial programming, and keep a copy of your MMSI in multiple locations on board.
Another major shortcoming in many installations is VHF that is not connected to GPS. Without this connection, your position will not be automatically transmitted during an ASN alert, forcing the emergency services to ask for your coordinates by radio or to locate you by goniometry, which considerably extends the response times. Always check that the GPS symbol appears on the screen of your VHF and that the coordinates displayed correspond to your real position.
An unsuitable or faulty antenna dramatically reduces the performance of your installation. An antenna of inadequate length, poorly tuned to marine VHF frequencies, or with a defect in its connection cable can divide your range by two or more. Cheap antennas for large nautical areas rarely offer the performances advertised. Invest in an antenna from a recognized brand and have its installation professionally checked if you have doubts. The savings made upon purchase could cost you much more in terms of security.
A lack of knowledge of safety channels seriously hampers your ability to communicate effectively at sea. Too many boaters are unaware of the existence of channel seventy ASN or do not know that channel sixteen should only be used for initial calls. This confusion can lead to attempts to communicate on the wrong channels, wasting valuable time in emergency situations. Familiarize yourself with the main channels in your navigation area and program them in memory for quick access.
FAQ — Configuring your VHF for security
Is VHF mandatory on board a pleasure boat?
The legal requirement to have a VHF on board depends on your navigation division. For navigation in division 245 and beyond, a VHF equipped with the ASN system becomes mandatory. In division 240, less than six miles from a shelter, it remains optional but highly recommended for your safety. Beyond these regulatory considerations, VHF represents safety equipment that would be unwise to do without as soon as you leave the coast. Cell phones are not a reliable alternative at sea, as their range is limited and their signal is often absent beyond a few miles.
What is the difference between a VHF with ASN and without ASN?
A VHF without ASN only allows conventional voice communications on the various channels. In case of emergency, you must manually call on channel sixteen and explain your situation verbally. A VHF equipped with ASN can instantly send an automatic digital alert containing your identity and GPS location, even before you have said a word. This technology greatly increases your chances of quick rescue, especially if you are injured, stressed, or unable to communicate clearly. ASN also works for selective calls between ships, making it possible to contact a specific boat directly without going through a general call.
Can a portable VHF be used as the main means of security?
A portable VHF can help but should never be your main safety equipment for several reasons. Its emission power limited to one or two watts reduces its range considerably compared to the twenty-five watts of a fixed VHF. Its short antenna and low position near water further limit communication distances. Battery life is also a major constraint, only a few hours with intensive use. Finally, a portable VHF can be lost, drowned, or damaged during capsizing or sudden movements. Instead, think of it as additional emergency equipment, particularly useful in the annex, or as a backup if the fixed VHF breaks down.
How do I know if my VHF is properly connected to the GPS?
Several indicators allow you to verify this essential connection. On your VHF screen, a symbol representing a GPS antenna or a position indicator should always appear when the GPS is active and connected. Access the configuration or information menu of your VHF to display the GPS coordinates received. Compare these values with those of your on-board GPS or use a smartphone application to check the consistency. The coordinates should be the same within a few seconds of arc. Sail for a few minutes and check that the position displayed on the VHF is updated in real time. If no position appears or if it remains fixed, the connection presents a problem that must be resolved.
How often should you test your VHF?
A monthly test is a reasonable minimum for a regular browser, with a systematic check before each trip for those who browse less frequently. These tests should include verifying the power supply, the correct display of the GPS position, the clarity of the emissions, and the reception of surrounding communications. Take advantage of your navigation to exchange with other ships and ask them for feedback on the quality of your signal. Once a year, ideally during wintering, have your installation checked by a professional who will check the more advanced technical aspects such as emission power, antenna impedance adaptation and the general condition of the connections. This preventive maintenance ensures the reliability of your equipment when you really need it.
What to do in case of a change of boat or owner concerning the MMSI?
The MMSI is attached to the ship, not to the owner. If you sell your boat, you must inform the Agence Nationale des Frequencies of the change of ownership so that it can update its records with the contact details of the new owner. The buyer can keep the same MMSI, which will remain associated with the vessel. If you are buying a used boat, check with the seller which MMSI has been programmed in the VHF and be sure to have the information about you updated from ANFR. If you change boats, you need to request a new MMSI for your new boat and program it into your new VHF. Never attempt to reuse the MMSI from your old boat on a new one, as this would create dangerous confusion in emergency databases.
What VHF channels do you absolutely need to know for safety?
Channel Sixteen remains the universal distress and call channel that you must monitor at all times. Channel seventy is reserved exclusively for digital ASN alerts and works automatically in the background. Channel six is used for communications between ships to coordinate maneuvers and avoid collisions. Channels thirteen, fourteen and sixteen are used for communications with port authorities and traffic services. Channel sixty-seven allows you to call marinas and marinas. Weather channels vary from region to region, but in mainland France, watch for the reports broadcast by CROSS on specific channels announced regularly. Program these essential channels into your VHF memories for instant access.
Conclusion
The correct configuration of your marine VHF represents much more than a simple administrative or technical formality. Each setting, from programming the MMSI to the GPS connection, to the selection of standby channels, contributes directly to your ability to survive in the event of an emergency at sea. A misconfigured VHF turns this vital safety equipment into potentially dangerous false security, giving you the illusion of being protected when your distress call could not be properly answered by emergency services.
The essential settings that we have detailed throughout this guide constitute the minimum security base: a correctly entered MMSI, a functional and verified GPS connection, a constant watch on channel sixteen, and a complete familiarization with the distress button and the safety channels. The physical installation deserves just as much attention, with a quality antenna positioned correctly, and a reliable power supply. Modern tools like the Oria Marine IoT box can facilitate the centralized management of your navigation and safety data, thus strengthening your overall device.
Safe sailing is not just about having the right equipment, but about regularly making sure that it works perfectly. Get in the habit of checking your VHF before each departure, test it periodically, maintain it conscientiously and do not hesitate to call in a professional for annual checks. The sea remains an unpredictable environment where conditions can change rapidly. The day you have to press that red distress button, you will be infinitely grateful that you took the time to properly set up your VHF. Your life and that of your teammates can depend on it. Enjoy browsing, and may your VHF never be used in real distress situations, but always be ready to do so.
