You are on course 086°T, speed 11.7 knots. At 1013 you see a buoy bearing 088°T at a range of 4.8 miles. If you change course at 1019 to leave the buoy abeam to port at 1.0 mile, at what time will the buoy be abeam?
• Relative motion between your vessel and the buoy when you change course • How to calculate the time to travel a given distance at a known speed • The geometry of when an object is exactly abeam (90° from your new course)
• After you alter course at 1019, what will be your new track relative to the buoy if you want it abeam to port at 1.0 mile? • How can you use a right triangle or relative motion diagram to link your speed, the change in range from 4.8 miles to 1.0 mile, and the time? • What does it mean, in terms of bearing from your new course line, when the buoy is exactly abeam to port?
• Be clear on what happens exactly at 1019 (position, bearing, and range at the moment of course change) • Confirm the speed remains 11.7 knots during and after the course change • Check that your final time is later than 1019 and that the distance run between 1019 and abeam time matches your geometry.
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