Your vessel is on a course of 272° T at 15 knots. At 2113 a light bears 245.5° T, and at 2120 the light bears 227° T. At what time and at what distance off will your vessel be when abeam of the light?
• Relative motion and bearing change to a fixed object • How to find "time of abeam" using a running fix concept • Using speed-time-distance to convert minutes of time into miles run
• How many minutes elapse between the two observed bearings, and how far does the vessel travel in that time at 15 knots? • If you treat the two bearings as two lines of position (LOPs) from a fixed light, how can you project your track so that one of those LOPs becomes the abeam bearing (90° off your course)? • Once you determine how many minutes from the second bearing until you are abeam, how can you convert that time into distance off at abeam using your speed?
• Make sure you are using true bearings and the given true course consistently (all relative to true north). • Check that you compute distance run correctly: Distance (NM) = Speed (knots) × Time (hours). • Confirm that the abeam bearing is exactly 90° from your course line (either port or starboard, as appropriate).
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