Calculating radio range, VHF, aerial height and distress calls

VHF radio follows the line of sight. A masthead aerial fourteen metres up reaches a coast radio station thirty metres up out to a good twenty nautical miles, while a handheld set at head height barely manages five. Transmitting power makes little difference; height makes all of it.

For a distress call this means that anyone out of range will not be heard on VHF. That is why an EPIRB and satellite communications should be carried as well on a long passage, since neither depends on the horizon.

The radio installation counts as equipment and should be included in the sum insured. More important, though, is permission to operate it: marine VHF requires a radio operator's certificate. Transmitting without one is a regulatory offence. Your watersports legal expenses insurance would step in, but the problem is easily avoided.