VHF range at sea: how the waves travel, antenna height and transmit power

Published on 8 October 2026 · By Ricard Prehn, professional recreational skipper (PPER), Spanish Yacht Captain (capitán de yate), Yacht Captain up to 200 GT, GMDSS General Operator and sailing instructor for over 27 years

How do VHF radio waves travel?

In a straight line. Marine VHF works between 156 and 174 MHz, with waves about 2 metres long that neither follow the curve of the Earth nor bounce off the ionosphere like medium or short wave. They only get through while the two antennas can “see” each other over the horizon, plus a small bonus from atmospheric refraction.

Over the sea your antenna actually receives two rays: the direct one and the one bouncing off the water. Beyond a few hundred metres they nearly cancel each other out, so the signal falls off much faster than in free space: every time you double the distance you lose 12 dB (the signal drops to 1/16). That detail is why watts go such a short way.

It is the same idea as with lighthouses and navigation lights: if they cannot be seen over the horizon, they do not get through. Radio goes slightly further than light because the atmosphere bends it a bit more (hence 2.22 instead of the 2.08 used for a lighthouse’s geographic range).

How do you work out VHF range?

With the radio horizon formula: range in nautical miles ≈ 2.22 × (√h₁ + √h₂), where h₁ and h₂ are the heights of each antenna above the sea in metres. Two yachts with masthead antennas at 12 m hear each other out to about 15 miles; a coast station at 150 m and that yacht, to about 35.

Each antenna contributes its own horizon, and the range is the sum of the two:

Note the square root: to double your share of the horizon you have to quadruple the height. Moving the antenna from the stern (3 m) to the masthead (12 m) gains you almost 4 miles without adding a single watt. A yacht at 12 m and a motorboat at 3 m: 7.7 + 3.8 = 11.5 miles at most.

Does a 25 W VHF reach further than 1 W?

A little, but far less than you might think. Over the sea, the range power buys grows with its fourth root: 25 times the watts only multiplies the distance by 2.2. And once you reach the radio horizon, more power is useless: the curve of the Earth cuts the signal anyway.

With two rays over the sea, the signal falls with the fourth power of distance. So to reach twice as far with the same antenna you would need 16 times the watts. These are the ranges the simulator gives for typical cases:

Compare the motorboat rows: 1 W reaches 3 miles and 25 W reaches 7, because with such a low antenna power still rules. On the yachts, though, 25 W barely gains 5 miles over 1 W: they are already up against the horizon. And to the coast station, at 25 W, the limit is almost exactly the radio horizon.

What is the range of a handheld VHF?

Between two handhelds, a couple of miles. To a boat with a masthead antenna, about 5 to 9 miles, and to a coast station on a hill, 20 or more. A handheld loses on both counts: it transmits 5 W and its antenna is a metre and a half above the water.

That is why the handheld is the radio for the tender, man overboard and the liferaft, not the main radio on board. If it is all you have, get as high as you can to transmit (flybridge, standing in the cockpit) and keep the antenna vertical: lying flat, you lose a lot of signal.

Why can I hear someone who cannot hear me?

Because they transmit with more power than you. The path is the same both ways, but if the coast station or a boat with a fixed VHF sends 25 W and you use a 5 W handheld or low power (1 W), their signal reaches you and yours falls short. Hearing someone does not mean they can hear you.

In the simulator you can see it by choosing «5 W portátil» and «Costera»: at some point the display reads «TÚ LES OYES, ELLOS A TI NO» (you hear them, they don’t hear you). In real life that is the moment to think: if you hear the coastguard clearly and they do not answer, they are not ignoring you; head towards the coast, raise the antenna or switch to high power.

When should you use low power (1 W)?

Whenever it is enough: in harbour, with the marina, between nearby boats or with your crew. With 1 W you reach a few miles without blocking the channel for every boat on the coast. Channels 15 and 17, for on-board communications, are limited to 1 W. For a distress call or when nobody answers, high power.

The rule of thumb is to start on low and switch up only if they cannot hear you. For a MAYDAY, the opposite: always high power, on channel 16 and, if your VHF has DSC, press the red button first. And spell your boat’s name with the phonetic alphabet: when the signal is marginal, that is what gets through.

How to get more range from your VHF

• Antenna as high as possible. On a yacht, at the masthead. Nothing else gains as many miles.
• Cable and connectors in good condition. A corroded connector at the mast foot eats more signal than dropping from 25 W to 5 W. Check it when you lay up.
• Emergency antenna on board. If you are dismasted, the masthead antenna goes with the mast. A spare on the pushpit gets you some miles back.
• Certified installation. On Spanish-flagged boats, fitting a fixed VHF requires an authorised installer; see this article (in Spanish).
• Do a radio check before leaving. With the marina or another boat, on a working channel, never on 16.

Why does VHF sometimes reach much further?

Tropospheric ducting. In summer, under high pressure and calm seas, layers of air form over the Mediterranean that guide the signal like a pipe and you can hear stations hundreds of miles away. It is real but unpredictable: never count on it when planning.

Beyond VHF range, the distress system (GMDSS) relies on other means: medium wave, satellite and NAVTEX for warnings. The area covered by coast-station VHF is called sea area A1, and it is where nearly all leisure boats sail.

The figures in this article come from a simple propagation model (two rays over the sea and a radio horizon with standard atmosphere) with typical antennas and receivers. They help you understand why and compare cases, not plan a passage.