At 1825 your GPS position is LAT 41°04.9'N, LONG 72°42.1'W. You are on course 085° per standard magnetic compass at a speed of 10 knots. At 1910 your GPS position is 1-mile due south of Twenty-Eight Foot Shoal Lighted Buoy. What were your set and drift?
• Set and drift (direction and speed of current) calculated from difference between DR (dead reckoning) position and GPS (fix) position • Using time–speed–distance: know how far you should have gone through the water vs. where you actually ended up on the chart • Plotting bearings and positions on the chart, including the position 1 mile due south of a known buoy
• How long were you underway between the two GPS positions, and how far should you have traveled at 10 knots in that time? • After plotting your course and distance from the 1825 position, where is your DR position at 1910, and how does that compare with the actual GPS-based position near Twenty-Eight Foot Shoal Lighted Buoy? • From the DR position to the actual 1910 position, what is the direction (set) and how many miles in that time (drift in knots)?
• Be sure to convert time from minutes to hours correctly before using the speed formula • Measure the distance and true bearing from DR position to actual 1910 position carefully on the chart • Remember that set is a true direction and drift is speed in knots, so compare both to the multiple-choice options
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