Your vessel is on a course of 144°T at 16 knots. At 0126 a light bears 166.5°T, and at 0152 the light bears 189°T. At what time and distance off will your vessel be when abeam of the light?
• relative bearing change and CPA (closest point of approach) • relationship between time, speed, and distance run • using tan of the bearing angle from track line to find distance off abeam
• How much did the vessel travel (in miles) between the two observed bearings, and over how many minutes? • What is the angle between your course (144°T) and each of the observed bearings (166.5°T and 189°T), and what does that tell you about your track relative to the light? • Once you know your speed and the extra time needed to reach the abeam position, how can you get the distance off at abeam using right‑triangle relationships?
• Convert all times to minutes and compute distances using Speed = Distance / Time (remember 1 hour = 60 minutes) • Carefully find the difference between course and bearing for each sighting and at abeam (90° from the light) • Ensure your final distance off matches the distance run between your last observation and the abeam time, using consistent units (knots and nautical miles)
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