Running Fix

A useful non-GPS navigational technique. Whereas the ordinary fix crosses Position lines taken from two or more objects as nearly simultaneously as possible, the running fix uses observations separated by an interval of time. One or more objects may be used to provide the position lines. The essential third item of knowledge is the distance and track made good between observations. For example, two position lines are obtained from a single wireless mast ashore at an interval of, say, ten minutes. If they are now drawn on the chart and the vessel’s track is drawn to scale, there can be only one position where it will fit between those lines. (The technique might equally be known as a ‘running fit’ and it may become clearer.) For success the boat must be steered on a constant heading and distance must be assessed as carefully as possible with allowance for stream, current and leeway due to the wind.