ABSTRACT
The Decca Navigator is a medium range electronic position fixing system based on hyperbolic principles. A chain normally comprises a master transmitting station and three slaves (Figure 6.1). Signals received aboard the vessel are compared in phase; the phase difference between master and slave is a measure of the vessel’s position within a lane. Until recently, position was indicated by means of Decometer readings. These readings are plotted on a special chart, overlaid with a series of hyperbolic lattices. The lattice charts can be used normally for navigation as they contain all the necessary navigational data (unlike the plotting charts produced by some governments) and are kept corrected by means of Notices to Mariners.
