Your vessel is on a course of 082°T at 19 knots. At 0255 a light bears 059.5°T, and at 0312 the light bears 037°T. At what time and distance off will your vessel be when abeam of the light?
• Relative bearing change and when a light is "abeam" (i.e., 90° on your starboard or port side) • Using time and speed to find distance run between bearings • Constructing or imagining a simple relative-motion triangle with your course and the observed bearings
• How does the bearing to the light have to relate to your ship’s course when the light is exactly abeam? Think in terms of a 90° angle. • From 0255 to 0312, what distance have you run at 19 knots, and how can you use that with the two bearings to estimate when you’ll reach the abeam position? • If you sketched this to scale on a plotting sheet, where would the light lie in relation to your track when the bearing change stops increasing toward your bow and becomes 90° off your beam?
• Be sure you are clear on what abeam means in terms of relative and true bearings. • Convert the time interval between observations to hours correctly before using speed-distance calculations. • Check that your final time is after the second bearing and that the distance off is reasonable compared with the distance run between 0255 and 0312.
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