Marine VHF radio: what is it actually for?

The marine VHF radio (Very High Frequency) is the most direct way to communicate at sea: with another boat, a port, a harbour office, or rescue services (MRCC/CROSS). Where a phone may lose coverage, VHF remains a reliable, simple tool designed above all for safety.

In practical terms, it’s used to: announce a manoeuvre (passing, entering port), contact a harbour office, communicate boat-to-boat (group cruising), and raise an alert in case of trouble. Once you understand the basics (range, settings, channels), using it becomes very natural.

How does a VHF radio work (simple explanation)?

A VHF works like a “marine walkie-talkie”: press to talk, release to listen. This logic is called simplex (only one person talks at a time). Some channels are duplex (two separate frequencies: one to transmit, one to receive), often used for specific communications with shore stations.

What are the key parts that make a VHF work?

A VHF relies on four key elements: the radio unit (fixed or handheld), the microphone (with PTT button), the antenna (essential on a fixed VHF), and power (the boat’s battery or an internal battery on a handheld).

VHF transmits on marine frequencies around 156–162 MHz. You don’t need to memorize that, but it explains something important: these waves mostly travel “line-of-sight”, a bit like a spotlight. The higher and better-installed the antenna, the more effective the communication.

VHF, UHF, CB: what’s the difference?

This is a common question: a marine VHF cannot communicate with a CB. CB doesn’t use the same frequency band, channels or uses. UHF is another frequency range, often used for other radio networks (professional radios, handhelds, etc.). In other words: even if it looks like a radio, it’s not the same “language”.

What is the range of a marine VHF radio?

A VHF’s range mainly depends on line of sight. In practice, VHF “sees” farther if the antenna is high and nothing blocks the signal (terrain, cliffs, buildings, heavy weather). That’s why a fixed VHF with an antenna at the masthead doesn’t behave like a handheld held in your hand.

Why does VHF range vary so much from one boat to another?

Here are the factors that most affect range:

• Antenna height: the higher it is, the greater the range.
• Coaxial cable quality: a worn cable “eats” your signal without you noticing.
• Connectors (oxidation, poor contact): a classic cause of laughably short range.
• Power (1W / 25W depending on models): useful, but less decisive than the antenna.
• Environment: terrain, weather, radio traffic, electrical noise on board.

How to set a VHF: squelch, power, watch?

A poorly set VHF can make it feel like it “doesn’t work” when it actually does. The three settings that matter most are squelch, power and watch.

What is squelch (and how do you set it)?

Squelch is a “filter” that cuts radio hiss when nobody is talking. Too tight and you won’t hear weak signals. Too open and you’ll hear constant noise. The simple method: open it until you hear a slight hiss, then close it just enough for the hiss to disappear.

Low/High power: when to use 1W or 25W?

Most VHFs offer low power (often ~1W) and high power (often ~25W). In practice: low power for close-range communications (port, manoeuvres, anchorage), high power if distance increases or reception is difficult. Keeping low power by default also avoids unnecessarily cluttering the airwaves.

Dual watch / Tri-watch: what is it for?

Dual watch lets you listen to Channel 16 (safety) and your working channel (port, intership) at the same time. In practice, it’s an excellent setting as soon as you’re underway. Tri-watch adds a third channel depending on the model.

Which VHF channels to use (16, 9, 72…) and why?

VHF channels are pre-programmed. The idea isn’t to know them all, but to remember the logic: you call on a designated calling channel, then switch to a working channel if needed.

Which channel should you monitor on VHF (the basics)?

The best-known reflex: Channel 16 is the calling and distress/safety channel. You use it to contact a station, report an emergency, or keep a safety watch at sea. Then, if the conversation needs to continue, you agree to switch to another channel.

Channel 9, 72, 77… how do you find your way around?

Many ports use Channel 9 as a calling channel (it depends on the area). Between boats, you’ll often find intership channels (depending on local rules and common use). The key is to stay brief, clear, and avoid monopolizing a safety channel.

DSC: what are the “DISTRESS” button and the MMSI for?

DSC (Digital Selective Calling) is a major safety feature. On a DSC-capable VHF, you can send a digital alert (for example via the DISTRESS button) that transmits the vessel’s identity and, if the VHF is connected to GPS, its position.

What is the MMSI?

The MMSI (Maritime Mobile Service Identity) is a 9-digit identifier associated with your radio installation. It helps rescue services identify the vessel and call you back more easily. It’s especially useful in a DSC alert.

VHF + AIS: a reassuring duo for navigation

Some setups combine VHF and AIS (or use separate equipment). AIS exchanges position information between vessels (depending on equipment) and improves traffic awareness. If you want a simple explanation of AIS benefits and limits, you can read: our AIS technology guide.

How to make a VHF call: ready-to-use phrases

VHF works best when you’re brief and understandable. No need for complicated language: a few habits are enough. Here are simple scripts you can adapt.

VHF calling procedure for a harbour office (example)

Calling channel (often 9 or another depending on the port): “Harbour office of [Port name], harbour office of [Port name], this is [Boat name], over.”
If they answer: “This is [Boat name]. Requesting a berth for the night / information. We are at the channel entrance. Over.”

Boat-to-boat communication: how to talk without clogging the channel

Identify the other boat first, give your name, state the purpose, and suggest a working channel if it may take time. Example: “Vessel [Name], vessel [Name], this is [Your name]. Can you confirm your intention at the crossing? Over.”

Emergency: the words that matter (and those to avoid)

At sea, some words have a precise meaning. The best known: “MAYDAY” is reserved for distress (grave and imminent danger). In plain terms: it’s not a word to use “for testing” or “as a joke”. If it’s serious but not immediately life-threatening, use an urgency message (for example “PAN-PAN”, depending on the situation).

Do you need a licence or an SRC/CRR to use a VHF?

Regulations mainly depend on where you sail (French waters or international) and the type of VHF (handheld, fixed, with DSC). The goal here isn’t to overwhelm you, but to give the clearest logic: the more “powerful” and “advanced safety” (DSC) the equipment is, the more requirements there are (training, licence, identification).

If you sail abroad, an SRC/CRR (or equivalent) is often requested. In France, requirements can differ depending on the case (non-DSC handheld, fixed, DSC). If you’re unsure, the best approach is to check based on your exact setup.

VHF antenna: placement, cables, common mistakes

A large share of VHF problems come from the antenna, not the radio. A fixed VHF without an antenna (or with poor connections) may transmit very poorly and can even risk damaging the equipment. On a powerboat, the antenna is often mounted high (T-top, arch, gantry). On a sailboat, a masthead antenna offers better range, but requires a longer cable (so the installation must be done carefully).

The 5 installation mistakes that ruin a VHF

• Coaxial cable too long or low quality, with major losses.
• Poorly crimped or corroded connector: the signal “gets lost” at the junction.
• Antenna too low: disappointing range even on high power.
• Routing near noise sources (some looms, converters, etc.).
• Testing transmission without a suitable load (depending on equipment): always follow the manufacturer’s recommendations.

Why won’t my VHF transmit or receive? (troubleshooting)

When a VHF “doesn’t work”, you can almost always isolate the cause with a simple method. The idea is to check the most common causes first before blaming the radio itself.

Symptom: “I receive, but no one can hear me”

• Power left on Low: switch to High if you’re at a distance.
• Mic / PTT: possible bad contact (try another mic if compatible).
• Antenna connection: #1 cause on fixed VHFs (corrosion, looseness).
• Faulty antenna: impact damage, ageing, water ingress.

Symptom: “I hear nothing (or almost nothing)”

• Squelch too tight: open it, then close gently.
• Volume (simple but common): also check for a silent mode.
• Channel: make sure you’re on an active channel (16 for an audio check, or a port channel depending on the area).
• Antenna/cable: weak reception often indicates a tired installation.

Symptom: “Terrible range, even on high power”

In most cases, it’s antenna + cable + connectors. A little corrosion or a damaged cable can easily cut range by a large margin. If you want to improve your installation long-term, prioritize a proper inspection of the antenna line.

Which VHF to choose: fixed or handheld, with or without DSC?

The right VHF mainly depends on your programme: day trips near the coast, regular cruising, night navigation, more isolated areas… The goal is to have equipment that’s easy to use and genuinely helpful the day you need it.

Fixed VHF: for whom?

A fixed VHF is ideal if you go out regularly and want stable range. It’s powered by the boat’s battery, can be linked to GPS (depending on the installation), and uses a dedicated antenna. In return, the installation needs to be properly done.

Handheld VHF: for whom?

A handheld is excellent as backup (in a waterproof bag), for a dinghy, at anchor or for a small boat. Its range is more limited (lower antenna), but it offers great flexibility.

With DSC: why it’s a real plus

DSC becomes particularly valuable if you sail often, sometimes single-handed, or want to send a structured alert quickly. Provided you configure identification correctly (MMSI) and ideally position (GPS).

Recap: using your VHF in practice

• Volume OK + squelch correctly set
• Channel 16 easily accessible (or dual watch enabled)
• Power on Low by default (High if needed)
• If fixed VHF: antenna connection looks clean, no looseness
• If handheld: battery charged, waterproofing (seal) checked