How do I choose and install a VHF marine antenna for my boat?

Choose a vertically polarised, 50-ohm marine VHF antenna suited to your boat's movement, then mount it as high as practical with a clear view of the horizon. Good coaxial cable, properly fitted waterproof connections and a sound mounting bracket matter as much as the antenna itself.

Plan the mount and cable route

Before buying, measure the full cable route, including bends, deck entry and the connection behind the radio. Check that the mounting surface can withstand the antenna's weight and bending loads. A long fibreglass whip puts considerable strain on a thin cabin roof.

VHF communication is mainly line of sight. Raising the antenna usually improves useful range more than choosing a higher gain figure.

• Sailing yacht: a short stainless-steel whip at the masthead is the usual choice. Leave clearance from the wind indicator, navigation lights and rigging.
• Motorboat: fit a fibreglass antenna on the cabin roof, radar arch or a suitable rail bracket, with its radiating section clear of surrounding metal.
• Small open boat: a shorter whip on a rigid console or elevated bracket is often more practical than a long antenna that flexes excessively.

Aim for an unobstructed view through 360 degrees and, where practicable, at least 0.5 metres of horizontal clearance from conductive structures. Keep the antenna outside radar and satellite communications beams. Never transmit while someone is working close to the antenna, and use proper climbing equipment for masthead work.

Choose antenna length and gain

Buy an antenna designed for marine VHF voice communications around 156 to 162 MHz, with 50-ohm impedance, vertical polarisation and a power rating of at least 30 W for a normal 25 W fixed radio. Its specification must cover the channels your radio uses.

On a sailing yacht, a whip roughly 0.9 to 1.2 metres long gives a broad vertical radiation pattern that works well as the boat heels. On a relatively steady motorboat, a fibreglass antenna roughly 2.4 metres long can provide a useful, flatter radiation pattern. Very long, high-gain antennas suit steadier platforms. Pitching and rolling can tilt their strongest signal away from the horizon.

Compare gain figures only when they use the same reference: dBi and dBd are different. Check whether the antenna needs a ground plane. Many marine designs are self-contained; follow the manufacturer's mounting instructions.

If fitting AIS as well, use separate antennas with the specified separation or an active splitter explicitly approved for your VHF and AIS equipment, including AIS transmission where applicable. Some Furuno AIS installations specify 2.8 metres vertically between antennas, or 10 metres horizontally at the same level. These requirements apply to that equipment; they are not universal small-boat dimensions.