Specifying position


The obvious way to specify your position is by latitude and longitude, probably by reading it from the display of a GPS set. This is always acceptable, but it may not be the best option. In some situations, it should be treated with particular care.


Check that the position indicated by the GPS is valid: if the GPS has been switched on within the past few minutes, or if its antenna has been damaged, it may not be showing the true position.


If the battery voltage is low, such as by self-discharge through flood water or by continuously-running pumps, the added power drain of transmitting on the radio may lower the voltage so much that the GPS switches itself off.


Latitude and longitude are meaningless to a listener until they are plotted on a chart. To many local boats, something like “half a mile south of Gull Rock” or “the eastern side of Spit Sand” would mean a lot more. It is quite acceptable, and sometimes most appropriate, to give positions by reference to a well-known and charted landmark.


To conform to the International Marine Vocabulary, you should give the direction first, followed by the name of the landmark, and finally the distance:-


Remember the order of things by imagining that you are giving directions to a helicopter pilot:- such as “fly south from the lighthouse for three miles”.


Remember that the hypothetical helicopter will be flying from the landmark towards you: make sure you don’t send him the wrong way!


 


Unless you specify otherwise, it will be assumed that bearings are in degrees true, and distances are in miles.

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