Although there is still a place in modern shipping for much older communications systems such as flags, lamps and sounds, these are not the focus of this work which is concerned with the various types of electronic systems mostly connected with the subject.
A vast array of communications equipment is carried on modern ships. Leaving aside personal devices such as mobile phones and computers able to connect to 3G and 4G data networks or wi-fi hotspots, the lowest level of marine communications is the VHF radio.
VHF operates on a range of frequencies with each frequency given a channel number. There are more than 80 channels but not all are used for marine purposes.
While many channels are allocated by international agreement for specific purposes, others are reserved for specific communication purposes by national maritime authorities or VTS systems.
The following VHF marine frequencies have been set aside by the ITU for particular purposes. These frequencies are internationally accepted by most nations and will be found on all VHF Marine Radios regardless of where or by whom they are manufactured.
- Channel 16 (156.800 MHz) - The international distress, safety and calling frequency.
- Channel 70 (156.525 MHz) - Digital Selective Calling frequency.
- Channel 13 (156.650 MHz) - Bridge to Bridge navigation frequency.
- Channel 06 (156.300 MHz), Channel 10 (156.500 MHz), Channel 67(156.375 MHz), and Channel 73 (156.675 MHz) Have been set aside for coordinated search and rescue operations.
Many countries have assigned closely related safety communications traffic to these frequencies as well as their primary SAR usage. Channels can be either simplex or duplex. Simplex is where both transmitter and receiver are operating on a single (or the same) frequency, for example VHF CH12 and VHF CH 16. On simplex channels it is not possible to transmit and receive simultaneously.
Simplex channels are mainly used for distress, urgency, safety and routine calling purposes, port, pilotage, harbour and inter-ship operations. Conversations on simplex channels can be heard by all receivers operating on the same channel.
Duplex channels are normally only used for communication between vessels and coast radio stations and for port operations and ship movement. With duplex channels transmissions can only be heard by the coast radio station. However, all ship stations listening to the same channel can hear the coast radio station transmission.
VHF radios can be fixed or portable. The fixed equipment is housed on the bridge or radio room and will likely be part of the ship’s GMDSS equipment. It will be used for bridge to bridge communications and conversations with VTS etc.
Portable VHF radios are used on ships for routine on board communications such as when mooring and unmooring or during cargo handling when conversations may take place between the ship and stevedores ashore. Some portable VHF sets will have GPS and DSC capability meaning they can be used for both routine and GMDSS purposes.
The IMO performance standard requires that portable VHF equipment intended to be used in lifeboats and liferafts should:
- provide operation on VHF channel 16 (the radiotelephone distress and calling channel) and one other channel
- be capable of operation by unskilled personnel
- be capable of operation by personnel wearing gloves
- be capable of single-handed operation, except for channel changing
- withstand drops on to a hard surface from a height of 1m
- be watertight to a depth of 1m for at least 5 minutes, and maintain watertightness when subjected to a thermal shock of 45°C
- not be unduly effected by seawater or oil
- have no sharp projections which could damage survival craft
- be of small size and weight
- be capable of operating in the ambient noise level likely to be encountered on board survival craft
- have provisions for attachment to the clothing of the user
- be either a highly visible yellow/orange colour or marked with a surrounding yellow/orange marking strip
- be resistant to deterioration by prolonged exposure to sunlight.
Approved VHF sets of fixed and portable and both GMDSS and non-GMDSS types are freely available at almost every port from ship chandlers and specialist equipment providers. Prices vary but the normal outlay is between $100 and $200 for a handheld VHF and fixed sets costing around double that.