Can I use my phone as a VHF radio at sea, and what are the limitations?

Your phone cannot work as a marine VHF radio on its own because it lacks the transmitter, receiver and aerial needed to communicate on marine VHF channels. Keep it as a backup for calls, weather and passage tracking, but use a marine VHF to communicate directly with nearby boats and coastguard stations.

Check what the app does

Check whether the app needs mobile data, Wi-Fi or a separate radio connected to it. This tells you whether it provides an internet service or controls radio equipment.

• Internet voice apps: connect participating users through data networks. They do not make your phone transmit on Channel 16, even if the screen looks like a radio.
• Radio streaming apps: may let you listen to a channel received elsewhere. They cannot provide a dependable local listening watch or transmit your distress call.
• Apps linked to onboard equipment: some systems let a phone control a compatible marine radio through Wi-Fi. The installed radio and aerial still do the transmitting; check which functions the manufacturer supports.
• Passage-tracking apps: services such as SafeTrx help share trip information, but updates need connectivity. They do not replace a VHF distress alert.

A waterproof case protects a phone from spray. It does not add radio capability or guarantee that the touchscreen will work with wet fingers.

Mobile coverage and VHF range

A mobile phone needs a usable connection to a shore-based network. Coverage can disappear close to land because of cliffs, headlands, network layout and your position in the boat. Reception at the marina tells you little about coverage along your route.

Marine VHF communicates directly between radios without a mobile network. Its range mainly follows the radio horizon, so aerial height has a large effect on how far a signal reaches.

• Fixed VHF: typically transmits at up to 25 watts. With a high, properly installed aerial, about 30 nautical miles is a useful guide in favourable conditions, especially when contacting an elevated coast station.
• Handheld VHF: commonly transmits at 5 to 6 watts. Expect roughly 3 to 5 nautical miles in ordinary conditions, with less possible between low boats.

Neither figure guarantees a safety radius. A yacht's masthead aerial generally reaches farther than a handheld held just above the water. Damaged coaxial cable or corroded aerial connections can severely reduce performance.

Calling for help

A call on Channel 16 can be heard by several nearby vessels and coastguard stations within range. Those vessels may be able to help immediately. A telephone call reaches the person or service you dial; surrounding boats do not hear it.