GB190709145A - An Improved Apparatus for use in Manoeuvring Ships. - Google Patents

Abstract

9145. Grant, H. C. J. April 19. Determining and plotting bearings and courses.- Apparatus for use in manoeuvring ships comprises a plotting surface c, surrounded by circular scales a, b, a pivoted radial arm d which sweeps the scales, and a T-shaped cursor y carried by the arm and having two scales e, f marked with equal divisions. For convenience in laying off bearings or courses by the transverse limb of the cursor, the quadrants of the outer scale in which the radial arm must be set are indicated on the plotting table. Thus the N to E and the S to W quadrants are each marked N & W or S & E, and the other two are marked N & E or S & W. To prevent the scale f from being raised from the plotting surface by the central pivot, a spring hinged section g<1> is provided at its centre. The circular scales a, b are mounted so that they can be set in May position. The following illustration is given of the method of using the apparatus. The flag-ship is steaming N. 15‹ W. at 14 knots. The forming ship has a speed of 16 knots and is 6 knots away on the starboard beam of the flap-ship. What course should the forming ship steer to bring her 2 knots in advance of the flag-ship ? (1) Assuming the flag-ship to be at the centre of the board, her course is plotted by turning the radial arm d to a quadrant marked N & W, setting the index b<1> to the 15‹ division of the outer scale b, and drawing a line from the centre of the board along the edge of the plotting scale f. (2) On this line a point D 2 knots from the centre and a point G 14 knots from the centre are marked. (3) The arm d is swung counter -clockwise through an angle of ninety degrees and the present positio P of the forming ship is marked. (4) A line is drawn through G parallel to the line joining D, P, by setting the plotting scale along the line D, P and sliding the cursor the required distance. (5) The cursor is slid out 16 divisions on the scale e. (6) The plotting scale is turned until the zero division lies on the line through the point G. There will be two positions fulfilling these conditions. The correct one is easily determined by inspection. (7) The reading on the inner scale a opposite the index a<1> gives the required course of the forming ship. For convenience in laying off distances in anchoring and mooring problems, the radial arm d is preferably engraved with equivalent scales h of yards, fathoms, shackles, and cables, which are read with respect to an index i on the cursor.