Your vessel is on a course of 253°T at 18 knots. At 2027 a light bears 275.5°T, and at 2055 the light bears 298°T. At what time and distance off will your vessel be when abeam of the light?
• Relative motion between vessel and fixed object (the light) • Using time, speed, and bearing changes to find closest point of approach (CPA) and time abeam • Converting elapsed time at a known speed into distance run along track
• How far has the vessel traveled between the two observed bearings, and what is the relationship between that run and the change in relative bearing? • When your vessel is abeam of the light, what will the true bearing of the light be relative to your course of 253°T? • Once you know when you are abeam (time), how can you use your constant speed to determine the distance off at that moment?
• Confirm the elapsed time between the two observations and convert it to hours (or decimal hours) correctly • Use the Speed = Distance / Time relationship to find the vessel’s run between the two bearings • Make sure the final bearing when abeam is 90° off your course (either to port or starboard) and is consistent with the earlier bearings.
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