GB551165A - Improved navigational instrument - Google Patents

Abstract

551,165. Navigational instruments. PRINS, H. C. Aug. 6, 1941, No. 10011. [Class 97 (ii)] A navigational instrument for use in setting a ship to steer a true course comprises a movable graduated scaleadapted to indicate directly a true course to be steered and a second movable graduated scale adapted to be set to indicate directly the amount of alteration from the previous true course being steered which is required to arrive at the new true course to be steered. In the form shown, two internally-graduated rings 1, 2 are rotatably mounted in a gimbalsupported, non-rotatable ring 5 within a casing 7. The ring 1 (the true-course-finder ring) is graduated in quadrantal and three-figure notations. The ring 2 (the course alteration indicator ring) and the ring 5 are both graduated from 0 degree to 180 degrees in opposite directions from a forward zero. The various graduations are illuminated by a masked lamp 20. The rings 1, 2 may be locked together in any desired relative position by a pin 8, and may be rotated by means of a hand-wheel 12 and toothed wheel 9. The upper ring 1 may be locked against rotation by a pin 13. A lubber line L is marked on a bowl 16 attached to the non-rotatable ring 5. A glass cover 17 carried by the ring is fitted with a central socket 19 for locating an azimuth mirror or other bearing-taking device for use in conjunction with the graduations in the true-course-finder ring 1. Assuming the ship to be sailing on a true course as indicated by the ring 1 against the lubber's line L the zero of the ring 2 registering with the lubber's line, and it is desired to change to a new true course, a bearing is taken on a distant land mark, star &c. by an azimuth mirror guided in the socket 19 the bearing being observed on the graduations of the true-coursefinder ring 1. The rings 1, 2 are now simultaneously rotated by the hand-wheel 12 until the new course is registered by the ring 1 against the lubber's line, the course-alteration ring 2 then showing the difference (to port or starboard) of the old and new true courses. The head of the ship is now turned until the land mark again registers with the previously-ascertained bearing whereupon the helmsman is directed to hold the new course. He then observes his compass and steers by the new compass course, calculations to correct for the deviation error of the compass being thus avoided. The fixed ring 5 may be used in conjunction with the bearing-taking device to ascertain the angle between a distant object and,the fore-and-aft line of the ship.