The Presentation of Radar Information for Collision Avoidance

Extract

If a navigator wishes to determine the closest passing distance of his ship to any other ship by means of radar, it can be done quite simply by plotting the ranges and bearings of the other vessel's echo. The line joining the plotted positions will indicate the relative course of the other vessel and by extending the relative-course line the closest passing distance can be measured. With the existing method of measuring bearing by means of a mechanical cursor with its attendant possible in-accuracies, it is necessary to plot a number of positions and draw the relative-course line as a mean through the plotted positions. The time taken to establish the nearest approach is therefore comparatively long. If an electronic bearing cursor is used the time to determine the nearest approach can be reduced since the accuracy of the measured bearings will be higher, and fewer measurements required. It may, however, be inconvenient to move from the radar screen to the plotting table and if plotting is done on the face of the PPI or a reflection plotter, the accuracy may be poor, particularly if the nearest approach is determined by extending a relative-course line formed by two plotted positions close together, using a blunt wax pencil.