Sea users have a language all of their own, and when you add the terms brought in by new technology and the demands of a specialised operation such as the lifeboat service the potential for confusion can be enormous! In The Lifeboat we try to explain some of the terms as we go, but readers have often asked us for more explanations of technical terms.

So here it is, the first in our occasional series of Lifeboat Lexicons.

Usage varies and we have had to generalise in places, so experienced sailors will have to bear with us while we attempt to unravel some of the mysteries… Radio VHP In the maritime context 'VHP' is a type of two-way radio which uses Very High Frequency radio waves. The sets are compact (not much bigger than a car radio), relatively inexpensive and are fitted to all commercial and the vast majority of pleasure vessels- Hand-held sets are also available, they are very small and light and can be transfered with a lifeboat crewman to keep in contact with a casualty.

The range of VHP is limited to 'line of sight' (the aerials must be able to 'see' each other) and so the higher the aerials are mounted the better. The maximum ship-to-ship range is usually about 20 miles, although a Coastguard station with a cliff-top aerial may do better. A simple exam is needed for the certificate to operate a marine VHP.

The range of frequencies available is split into 'channels', some for ship-to-ship conversations, some for harbour control, some for ship-to-shore. One channel. Channel 16, is used to make initial contact before switching to a 'working' channel and is also used for all emergency work. The Coastguard has a private channel, Channel Zero, which lifeboats and other emergency services can use but which is not available for use by other vessels.

MF For longer range radio work MF, or Medium Frequency, radio is used. The signals can follow the curvature of the earth and are not limited to 'line of sight'. The sets are bigger than those for VHP (typically about the size of a large portable stereo) and use more electrical power. A more complex exam is needed for the certificate to operate them and although every commercial vessel carries an MF sets they are not often found on yachts or very small fishing boats.

DF The initials stand for Direction Finding, and DP equip- 1 can be used on both VHP and MF radios. A DF set matically calculates the direction from which a radio signal is strongest and displays the compass bearing to it If this is the casualty the lifeboat can then use the DF display to home in on the vessel. If two or more DF bearings can be obtained (perhaps from Coastguard stations ashore) then the actual position of the vessel can be found..