Abstract: A sailing course computer instantaneously and continuously computes a sailboat's speed towards a predetermined destination. In a first embodiment, a polarizer disk is utilized as a compass card through which a light source may be directed. An analyzer disk is positioned below the polarizer disk, and a photocell below the analyzer disk then provides a signal indicative of the amount of light passing through the two disks in response to the sailboat assuming various headings. A second signal input is provided by a knotmeter, and appropriate electronic circuitry is then used to indicate the speed of the sailboat towards a given destination. In a second embodiment, a light source is provided on one side of a compass card and a photocell is provided on the other, with a circular aperture being positioned tangentially to the center of the card so as to permit light impingement from the light source upon the photocell.