Channel 16 VHF
Some nations allow the use of marine VHF 16 as an initial calling frequency; after an initial response the call is to be switched to one of the working channels, except in case of emergency traffic.
VHF channel 16 (156.8 MHz) is monitored 24 hours a day by coastguards around the world. In addition, all sea bound vessels are advised to monitor channel 16 VHF when sailing, except when communicating on other marine channels for legitimate business or operational reasons. Coastguards and others are permitted to broadcast short informative safety messages on channel 16, however, it is an offence in most countries to make false mayday calls. When using the channel to call up ships or shore stations, the call has to be switched to a working channel after the initial response in order to keep channel 16 available to others.
- http://www.nonprofitpages.com/11s14/MRWReq.html US Coast Guard Auxiliary, Rules Which Require Listening to your VHF Marine Radio