communication - page 2
7.2 Electronic communications
The field of Electronic Communication continues to explode, especially with the advent of digital signals, satellites and computers. As these electronic devices evolved, sailors immediately saw their advantages and embraced them. Even the curvature of the earth with its line of sight restrictions is overcome by single side band radios and global communications systems with satellites.
The VHF international maritime mobile band
VHF frequencies between 156.00MHz and 174.00MHz are allocated to the Maritime Mobile Service (MMS); for use by ships fitted with VHF radio. This allocation is made by international agreement to maintain order into what otherwise be a chaotic situation.
The band is divided into 59 channels with spacing of 25kHz between each. In addition, national authorities allocate a number of private channels.
Each channel is allocated for one or more of eight specific purposes an it is important to select a suitable channel for your particular use:
Distress safety and calling
Channel 16 - has always been the VHF Distress Safety and Calling frequency and will remain so for the foreseeable future. The introduction of DSC reduces congestion on Ch16 as the initial electronic alert is sent as a very short data burst using Ch70. Ch70 must never be used for voice communication.
Channel 13 - is an inter-ship channel reserved exclusively for bridge-to-bridge communication on matters of navigational safety.
Channels 6,8,72 and 77 - should be used for inter-ship working because they are exclusively for that purpose. Other inter-ship channels are allocated for additional purposes; for example Ch10 for pollution control and Ch09 for harbour pilots. Small Craft chould avoid using these channels.
Channels 11,12 and 14 - most commonly used for port operations but refer to a nautical almanac for local variations.
Ship movements (very similar to port operations)
Ship movements are often conducted on the single frequency channels such as Ch15, 17 and 69.