Patent GB-1438512-A (GB)
Title: Compass apparatus for indicating the extent of any deviation  from a selected compass course
IPC: G01C17/00
Filed: 1973-06-05
Abstract: 1438512 Compasses; indicating apparatus B HOWARD 5 June 1973 [5 June 1972 7 Dec 1972] 26766/73 Headings G1F and G1J A navigational compass comprising a pair of magnets 27 secured on a card 21 pivotally mounted in a housing 13 is provided with a course selecting and indicating arrangement in which an energy source 26 is arranged to energize, by way of a conducing path associated with the magnet, a portion only of an indicator associated with an adjustable course selector 14. As shown, a light source 26 mounted in the base of the compass directs light by way of a prism 29 to a slot 30 in the card 21 aligned with the N-S axis between the magnets 27. Such slot 30 allows the light to fall on one of a plurality of optical fibres 39 mounted such that their lower ends 38 are annularly spaced about the pivot axis of the magnet 27 and their upper ends 39a are annularly spaced on the adjustable selector 14 whereby one of the upper ends 39a lights up. The fibres are long enough to permit rotation of the selector and their upper ends are arranged in the opposite rotational sense relative to their lower ends so that the order of sequential illumination is reversed. A further optical fibre 39b arranged between the lamp 26 and the top of the housing adjacent the course selector 14 provides a reference mark 39d at the lubber line. In use, with the compass mounted on a boat, the helmsman adjusts the selector 14 until the desired course is registered opposite the reference mark 39d, and then steers the boat so that the lit-up optical fibre 39 is aligned with the reference mark 39d, this being indicative of the correct course being steered. In an alternative embodiment, Figs. 8 and 9 (not shown) instead of optical fibres, individually spaced neon lamps (61) on the selector are connected by individual flexes, (63) long enough to permit rotation of the selector, to respective conductors (58) adjacent the magnet. The lamps are arranged to light up individually when a circuit comprising an oscillator (64) and connected to a common conductor (56) is completed by a conductor (59) movable with the magnet between conductors (58, 58). In a further embodiment Fig. 11, light from a lamp 73 is directed by way of a reflecting surface 99 on a float 95 carrying magnets 96 and surfaces 93, 79, 78 to a panel on the selector, the surfaces 79, 78 being defined by diametral planes of light-transmitting half-cylinders 77, 76 arranged in the housing to be rotated at half the rate of the selector through gearing 82- 85, 87, about an axis coinciding with that of the magnet 96. Another embodiment, Fig. 6 (not shown), using optical fibres as in that of Figs. 1 (riot shown), 4, comprises a compass card 22 with magnets 124, 125 secured to a mark 127 having a slit 129 at the N position. The card 22 pivots on a transparent cover 119 of a light source 118. The compass housing 120 is transparent and includes. a depending lubbers line marker 128. The course selector ring 112 is rotatable relative to the  housing by a handle 113 and provides a channel for optical fibres which receive light, through a fixed transparent housing 120, at their ends 138 from the slit 129 and transmit it from their ends 139 to the ends 134 of further fibres in an upper housing member 114 on the rim of which their other ends 136 are exposed. The fibres in the selector ring 112 are reverse connected between their ends 138, 139, as in the earlier embodiment, although this does not show on the figure. A further fibre 143 provides a lubbers line indicator as before, its end 145 being displaceable by a handle 147 to lie opposite either one of two adjacent fibre ends 136.