Navigational and yacht racing calculator

A navigational calculator (10) for establishing the ratios of time, or distance, to be spent on port or starboard tacks, respectively, during the maneuvering of a yacht to a windward destination. A plurality of disk members are carried on a central support (11). The first disk member (14) has a true wind indicator (30) imprinted thereon. The second disk member (15) has a compass rose (34) imprinted thereon. The third disk member (16) has a course indicator (35) and two sets (38 and 39) of tack ratio indicia imprinted thereon. The fourth and fifth disk members (18 and 19) have starboard and port heading indicators (46 and 55, respectively) imprinted thereon. The sixth disk member (20) has included tacking angle indicia imprinted thereon and a tack ratio indicator (61) alignable with one set (38) tack ratio indicia. The seventh disk member (21) has included tacking angle indicia imprinted thereon and a tack ratio indicator (66) alignable with the other set ( 39) of tack ratio indicia. An eighth disk member (79) may be rotatably supported beneath the first disk member (14). By making the eighth disk member (79) of lesser diameter than the first disk member (14), and by providing similar logarithmic scales (81 and 84, respectively) on each, the calculator (10) can incorporate a circular slide rule (85).