GB253263A - An instrument for indicating ships courses - Google Patents

Abstract

253,263. Stuart, J. F. March 31, 1925. Plane-trigonometry calculators .-Consists of an instrument for determining the course of an observed ship in relation to her bearing when the range of the ship and the length of a horizontal fore-and-aft line on her are known. The ship is obset-ved through a window by means of a divided lens A, C, of which the movable part A is provided with an indicator K extending over a scale plate F. This plate is marked with a vertical scale m representing the known base lengths and co-operating with a vertically-displaceable indicator W. The plate is also marked with a range scale comprising lines radiating from a zero point j. Displaceably mounted on rollers R, T above the scale plate is an endless band M on which a horizontal line rt, equal to the breadth of the base line on the scale plate, is graduated according to the sines of angles from zero to 90‹ and the graduation marks are all joined to a point not seen in the Figure vertically below the point r. To use the instrument the half lens A is adjusted until the image of one end of the base line therein coincides with that of the other end of the base line in the half lens C. The indicator W is set to the known base length and the band M is then turned until the 90‹ line intersects the edge of the indicator W at the same point as the line on the scale g (the 14 line in the Figure) representing the known range of the ship. The desired course angle is then given by that line on the band M which intersects the indicator W at the same point as the indicator K, i.e. the 40 degree line in the Figure. When the angle subtended by the base is obtainable by separate means the divided lens may be omitted, the instrument then being provided with a subtense scale y on which the indicator K is set to the known angle. The instrument may also be used to obtain the range of a ship assuming her to be broadside on to her bearing. If the adjustment of the half lens A in this case brings the indicator K to the dotted line position K<1>, the range is given by the line on the range scale which intersects the indicator W at the same point as the indicator K i.e. in the Figure the range is 12,000 yards.