At 1712 your GPS indicates a position of LAT 36°54.8'N, LONG 75°39.8'W. You are on course 319° per standard magnetic compass at a speed of 9.9 knots. At 1800 your GPS indicates your position at LAT 37°00.0'N, LONG 75°45.8'W. What were the set and drift?
• Set and drift: set is the direction (in °T) the current pushes you toward; drift is the current’s speed in knots • Difference between DR (dead-reckoned) position and GPS (observed) position to find current • Converting time underway to hours to use with the speed-distance-time relationship
• From the course and speed made good through the water, where would your DR position be at 1800 if there were no current? Plot or calculate that first. • Compare the DR position to the actual GPS position: in what true direction (bearing) did the current push you, and how far? • Convert the distance between DR and GPS positions into drift (knots) using the elapsed time, then match that set and drift to the closest multiple-choice option.
• Be sure your time interval (1712–1800) is correctly converted into hours before computing distance and drift. • Carefully distinguish between course steered (319° by compass) and the set of the current: they are usually not the same direction. • When finding the current’s direction, take the bearing from the DR position to the observed GPS position and express it as ° True (°T) to compare with the choices.
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