GB1505246A - Navigational aids - Google Patents

Abstract

1505246 Navigational instruments GRUNDY & PARTNERS Ltd 11 April 1975 [5 Feb 1974 23 July 1974] 05146/74 and 32568/74 Heading G1F [Also in Division G4] An on-board navigational aid for preventing collision consists of an analogue computer for calculating and displaying the change in the "nearest approach distance" (p) to another vessel of known relative bearing, taking into account present speed, proposed speed alteration, proposed course alteration of "own" vessel and the time for which such proposed alteration is to be held. The computer may also take into account the range of the other vessel and may calculate a new value of p from a knowledge of the existing value derived e.g. from a radar display. The computer takes no account of the unpredictable changes in speed and course of the other vessel. In the headup, relative motion radar display of Fig. 1, the other vessel T has bearing # and range R=OP, and the "nearest approach distance" for present speed u and present course of own vessel V is given by p=OX. In the lower part of the diagram, a triangle of velocities O'CO shows present speed u, proposed speed alteration v and proposed course alteration A. The distance y=O D represents rate-of-change of p and by geometrical analysis (set forth in detail) this is given by the approximate equations:- The first Formula is preferred since the second one takes no account of R and p. The resultant new value of p is given by adding yt to the present value, where t is the time for which the proposed alterations are held. The computer of Fig. 4 derives p + yt using a value of y given by the first formula. Inputs u and v are set-up on the pots. P6, P5 respectively and the angles A and (A-#) on the resolves Re2, Rel. The two resolvers have ganged shafts so that # is set in both simultaneously. Rotation of the body of resolver Rel through angle A results in setting of (A-#) in this resolver. The sine and cosine outputs of the resolvers are both fed to respective adding amplifiers A4, A5, and a pot. P3 in the feedback path of A5 effects multiplication by I/R where R is the range input. Multiplication by p is effected by pot. P1 which is ganged to pot. P2, and the two halves of the expression for y are added by the amplifier A7. The time t is set in pot. P4 and the term yt added to p by the amplifier A8. The case of a divergent (instead of convergent) other vessel T is discussed. The bearing of such a vessel changes clockwise (instead of anti-clockwise) if navigation rules are obeyed, and this involves reversal of the value p which can by accounted for in the amplifier A9 and pot. P2. The value of y is also (conventionally) reversed to give a (conventional) negative value of the new p. For this purpose a switchable inverter A6 is included in the circuit. The Specification describes an input and display panel Fig. 3 (not shown). This incorporates a X4 output range switch. The computation may also be performed by a programmed digital computer connected to the input resolvers and pots. through an A/D converter.