IT has long been realized that the small fishing craft are inadequately supplied with modern navigational aids, and the reason why the most modern aid, radar, is not used is because its cost, weight and electrical power requirements are too great. In Great Britain a large number of small-boat fishermen, for instance in the herring drifter fleets, use Consol for offshore navigation, but this is not sufficiently accurate for navigating into harbour in bad visibility.

In 1951 the National Research Council of Canada undertook the development of a microwave course beacon as an aid to entering harbour. In 1953 the Ministry of Transport & Civil Aviation Group at the Admiralty Signal & Radar Establishment undertook the development of a similar beacon with a view to simplifying the shipborne equipment.

The beacon system is an adaptation of the old Lorenz type aircraft landing aid and consists of a microwave radio transmitter mounted at a harbour entrance and radiating in turn from each of two aerials which have beams overlapping in the horizontal plane. The transmitter is so sited that the line of intersection of the two beams lies along the safe course line for entering harbour. (Fig. 1 shows the orientation of the beams at the Scottish fishing port of Arbroath.)