Your vessel is on a course of 079° T at 11 knots. At 0152 a light bears 105.5° T, and at 0209 the light bears 124° T. At what time and at what distance off will your vessel be when abeam of the light?
• Relative bearing change and when a light is "abeam" (i.e., at 90° from your heading) • Using the time between bearing observations to find distance run and construct a running fix • Basic speed-time-distance: Speed = Distance / Time and similar triangle geometry on a course line
• How much did the bearing of the light change between the two observations, and what does that tell you about its relative motion as you proceed on a steady course? • When the light is abeam, what will its true bearing be relative to your true course of 079° T, and how can you extend your existing bearing lines to find that point? • Using your ship’s speed and the time intervals, how can you convert the geometry of the bearing lines into the distance off at the abeam point?
• Be clear on what bearing corresponds to the light being abeam of your vessel, given your course of 079° T. • Convert the times (0152 and 0209) into minutes and use your 11-knot speed to compute the distance run between bearings. • Check that your chosen answer’s time is consistent with the additional distance you must steam from the last observed bearing until the abeam position.
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