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.
Radio – Telephones
In addition to the VHF radiotelephone there are other electronic devices that serve sailors well depending on how far offshore they travel. These devices are more expensive and controlled than the VHF radios just discussed. This is often a matter of formal training and licensure.
The best device is the single-sideband (SSB) radio that has the capability to communicate beyond the line of sight distance limitations of VHF. SSBs are permitted to transmit at 50 to 150 watts. There are some restriction and limitations on the use of SSBs. These radios also have the ability to receive weather faxes and other constantly updated information. When sailing offshore a single side band radio is essential.
Ordinary cell phones often work well within their “cell” areas. Cell range is approximately line of sight and will vary with the cellular telephone provider. The best advice for cell phone use is to test them in the area you normally sail before relying too heavily on their use.