When you’re out sailing it’s likely you’ll need to communicate with others around you (for instance to relay information or to raise an alarm), and the way you do this onboard is via your VHF radio.
The VHF radio band is divided up into different channels, many of which have a specific designated purpose. Channel 16 is perhaps the most well known (and important!) as it’s the international distress, safety and calling channel. All vessels equipped with VHF radios are required to maintain a listening watch so messages of distress are likely to be heard. Because most boats are listening, Channel 16 is also used to initially hail other parties. Once contact has been established the conversation is switched to a “working channel” to free 16 up again. Here’s a list of channels and their usage if you’re in the US (https://www.navcen.uscg.gov/?pageName=mtVhf), or in the UK (http://rnli-sarroc.org.uk/channels.html)
When you broadcast on a VHF channel every other vessel listening on that channel (within your radio’s range) will hear your message. Under normal circumstances you’ll be calling just one other party (a friends boat, or a marina) so no-one else will be interested in what you have to say. Therefore always keep communication short and to the point to avoid clogging up the channel and irritating other people!
These are routine calls to other boats and to shore stations. Conversations could be about reserving a berth for the night, arranging fuel or finding out when your friends boats is expected in the anchorage.
VHF radios can also be used to relay important safety information or to alert other vessels of something unusual in the area (floating debris or an unlit buoy are pretty common). Usually Securite calls originate from the coastguard but there maybe a time when you need to do one yourself.
There are two types of emergency call. A Mayday is used when there’s imminent threat to life or vessel. For example when someone has gone overboard, is unconscious or seriously ill. For the boat this could mean it is sinking or on fire. A PanPan us used when the safety of a person or boat is in serious jeopardy but there’s no immediate danger. For example a boat has been dismasted, or its lost its engines and is drifting towards a rocky shore.
The US Coast Guard and the Boat U.S. Foundation have put together a great (half hour) online tutorial called “Can You Hear Me?” which summarises the use of VHF and DSC radios. You can find it here. Good to know: the download only works for PC’s. If you have a Mac you’ll need the online tutorial. https://www.boatus.org/dsc/
Many countries require a license to operate a VHF radio. One of the main reasons is to help keep on-air conversations following specific protocols, which helps shape the communication and keep everything understandable. In some countries, like the U.S., laws allow recreational users to use VHF radios without requiring a license. Despite the lack of licensing in other countries, all users must adhere to the established communication protocols.