Your vessel is steaming on a course of 140° T at 15 knots. At 1530 a lighthouse bears 200° T. At 1550 it bears 249° T. What is your distance from the lighthouse at 1550?
• Relative motion between your vessel and the lighthouse using two bearings and a known course • Using distance = speed × time to find how far you travel between bearings • Right triangle / trigonometry idea: bearings giving you angle at the lighthouse or along your track
• Draw your ship’s track as a straight line and plot the two bearings from the lighthouse. What geometric shape do you get between the two positions and the lighthouse? • How far does the vessel travel between 1530 and 1550 at 15 knots, and where does that distance fit in your triangle? • Which angle in your triangle can you calculate from the given true bearings and course, and how can that help you find the distance from the lighthouse at 1550?
• Convert the 20 minutes between bearings to hours correctly before using speed × time • Be precise when finding the difference between your course (140° T) and each bearing to establish triangle angles • After computing the distance from the lighthouse, check if the value is reasonable compared to how far you traveled in 20 minutes at 15 knots
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