Marine Radio Communications
#1: Channel 68 is strongly discouraged as a choice for recreational vessel ship-to-ship communication in Canada, as it is the only channel authorized for use by Canadian shore facilities—for both hailing and working. Not only should 68 be kept clear for that use, but also your personal conversations on that channel are likely to be overheard by anyone within earshot of radio speakers at every marina within ten miles! For much the same reason, channel 9 should be used with restraint in the U.S.; for, although U.S. shore facilities may use channel 16, channel 9 is often their preferred working channel.
#2: Channel 70 must not be used for ordinary communication. It is reserved worldwide for Digital Selective Calling (DSC), a feature of the Global Maritime Distress Safety System (GMDSS). It's the channel a distress message goes out on when the mayday button on newer VHF radios is pressed. (Newer radios do not permit voice tranmission on channel 70.)
Cellular service is so prevalent throughout most of the Great Lakes that there is no longer radiotelephone ("ship-to-shore") service available through shore stations in the U.S. Phone calls can still be placed through Canadian Coast Guard stations, but at very high cost.
VHF channels available for communications between yachts are these:
9, 68 (but see Caution #1 above), 69, 71, 72, 78A, 79A, 80A
Weather forecasts are continuously available in the U.S. and Canada by tuning to "Wx" channels on VHF radios. Additionally, in Canada they can also be received on VHF channels 21B and 83B.
In Canada, Notices to Shipping are also broadcast on these channels, so it can be a frustrating wait for the weather information to come around.
What are A and B Channels?
The VHF radio channel structure is a world-wide system. In that system, some channels are "simplex", others are "duplex". On simplex channels a radio transmits and receives on the same frequency; thus one party must listen while the other speaks. On duplex channels, used exclusively for ship-to-shore communications, the shore station transmits on one frequency while the ship transmits on another. Both stations receive on the opposite frequency. That method allows two-way communication just like using a telephone, where both parties can speak and listen simultaneously. Most VHF radios on pleasure craft, however, are designed with push-to-talk microphones and are not capable of full duplex communication. This is called "semi-duplex".
Channels 78, 79 and 80, noted above in the list of inter-yacht channels, are established internationally as duplex channels. It is possible, however, to use one side of a duplex channel—after all, it's just another frequency—for simplex communications. When one of a duplex channel's two frequencies is used in this way, the channel number is given a suffix to indicate which of the two is being used. For example, the United States Coast Guard uses for in-house communications what would normally be the ship-transmit frequency of duplex channel 21. It's designated "21A". In Canada, weather broadcasts are transmitted on what would normally be the shore-transmit frequency of duplex channel 21. That's designated "21B".
VHF radios have a switch labeled "US/Intl" (or similar wording). When the radio is in international mode and is tuned to channel 78, for example, it will operate in the duplex mode. If the radio is in the U.S. mode, channel 78 will be in simplex mode. That's why sometimes two boats fail to make contact on "A" channels: one or both radios are in international mode and not listening on the "A" frequency.
For a complete list of the U.S. Marine VHF Channels, please click here
Report by Commo. Jim Acheson, M/Y Lady J