1 The horizontal angle between the intended direction of travel of a vessel and a reference direction, generally north. The angles between true, magnetic, and compass north and the path of the vessel are known respectively as true course, magnetic course, and compass course. The angular difference between the true and magnetic course is the variation, and that between magnetic and compass course is the deviation. The combination of variation and deviation is the magnetic compass error.
Nowadays the compass course of a ship is denoted in three-figure notation from 000° to 359°. With the gyro compass the readings will be true. See also great circle; lay (3); rhumb line.
2 In theory, the sails set upon the lower yards of a square-rigged ship to which bonnets could be attached. The original spelling for these sails was corps or corse. But the original definition of ‘course’ was extended to all sails set on the lower yards irrespective of whether they were adapted to carry bonnets, and they were designated by the name of the mast on which they were set, as fore course, main course, and mizzen course. Gradually staysails set on lower masts and the main staysails of brigs and schooners also became known as courses. A ship which set only foresail, mainsail, and mizzen was said to be under its courses. For illus. see square rig.