GB565301A - An instrument for use in navigation or course-finding - Google Patents

Abstract

565,301. Calculating - apparatus. THORPE, R. L. March 3, 1943, No. 3499. [Class 106 (i)] A navigation or coursefinding instrument for use on a ship, aircraft or other vehicle, for ascertaining the compass course or direction by conversion from the true course indicated by a chart or map, knowing the magnetic deviation characteristic of the ship &c., comprises a rectangular base member 10, Figs. 1 and 3, of transparent material with side members 12, 13 supporting a tablet 14 of transparent material with a longitudinal compass-card scale 15 along one edge graduated in degrees. Beneath the tablet 14 is a slidable strip 16 adjustably fixed in the upright 12 having a true-bearing scale 17 graduated from 0 degrees to 360 degrees. The tablet 14 carries subsidiary scales 18 and 19 denoting degrees of magnetic variation east and west and has inscribed thereon the known deviation curve 23. The curve is conveniently drawn with a soft pencil so that it may be easily corrected when opportunity occurs. The tablet 14 serves as a guide for the slides 26 of a cursor comprising relatively movable transparent plates 27 and 28. The plate 27 bears a pointer 29 and a marker line 31, while the plate 28 bears a pointer 30 and a marker line 32 arranged at an angle of 45 degrees to the line 31. The two plates are clamped in adjusted position by a stud 34 and nut 33 movable in a slot in the plate 27. The base member is supported on rollers 11 so that it may be traversed over a chart or map to determine the true bearing between the present position and the destination point. In operation, the true bearing on the scale 17 is set to the known variation at the present position. The cursor plate 28 is then moved until the pointer 30 registers with the point on the true bearing scale and the plate 27 is adjusted until the point of intersection of the marker lines 31, 32 registers with the curve 23 when the pointer 29 will indicate the compass course to be steered. In a modification, Fig. 4, the device is designed as an attachment to a known form of parallel ruler. The compasscard and true bearing scales are graduated on strips 151, 161 arranged in grooves on the face of the tablet 14 that is supported in a wooden frame 35 on the ruler base 101. The cursor plates 271, 281 are each provided with a slide part 261 and held together by the clamping nut 33. In another modification (not shown), the marker lines are formed as slots operatively connected by a slidable stud and means may be provided for positively guiding the cursor plates along the line of the deviation curve.