Radar and Collision at Sea

Extract

Captain Wylie's note ‘Radar and the Compass Bearing’ (Journal, Vol. VII, p. 200) voices the objection to the ship's-head-up display because it gives bearings relative to the fore-and-aft line instead of to the axis of the compass card. This objection will not appear to be a very real one to anybody accustomed to using a dumb-card pelorus: a glance at the compass, or a word to the man at the wheel, will give the correction to be applied to the bearing in order to make it relative to the course by compass. If the ship is a degree right of her course we add a degree, if two degrees left we subtract two, and so on, before using the bearing. If plotting, the plot is a COURSE-UP plot, not a ship's-head-up plot. It is, in fact, a compass-datum plot with a more convenient orientation than the north-up which is so strongly advocated. It would appear to be mere hair-splitting to regard the corrected bearings as not being compass bearings within the meaning of the Steering and Sailing Rules since the important thing is whether or not the bearing is changing appreciably and not the number of degrees it contains. However, this objection, and that of the angular displacement of the plotted tracks of targets when course is altered, can both be completely negatived by using the course-up, gyro-stabilized display; the heading marker is set to zero when the ship is on her course and the gyro allowed to take care of yaw.