Your vessel is on a course of 196° T at 17 knots. At 0417 a light bears 218.5° T, and at 0442 the light bears 241° T. At what time and distance off will your vessel be when abeam of the light?
• Relative bearings and abeam position (abeam is a 90° relative bearing from your heading) • Using course and two position lines (bearings) to find Closest Point of Approach (CPA) or abeam time • Speed–time–distance: ( \text{Distance} = \text{Speed} \times \text{Time} ) with correct unit conversions
• How does the change in bearing from 218.5° T to 241° T over 25 minutes relate to your vessel’s track and the light’s position? • What true bearing will the light show when it is exactly abeam of you, given your course of 196° T? • Once you know how long it takes from one observed bearing to abeam, how can you convert that time interval at 17 knots into distance in nautical miles?
• Confirm what ‘abeam’ means in terms of relative bearing (angle from your bow). • Carefully compute the time intervals in minutes between each bearing and the abeam time; then convert minutes to hours before using the speed–distance formula. • Verify that your final distance off at abeam is reasonable compared to how far you would travel in the total time from first sighting to abeam at 17 knots.
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