At 1620 your GPS indicates a position of LAT 41°09.0'N, LONG 72°40.0'W. You are on course 134° per standard magnetic compass at a speed of 10 knots. At 1700 your GPS indicates your position as LAT 41°05.3'N, LONG 72°33.7'W. What were the set and drift?
• Set and drift: set is the direction the current pushes you (in °T), drift is the speed of that current (in knots) • Difference between DR (dead-reckoned) position from course & speed, and the EP (estimated/GPS) position • Converting time underway into distance at a given speed to find how far you should have traveled through the water
• From 1620 to 1700, how many minutes have passed, and how many nautical miles should you travel at 10 knots in that time? • If you start at the first GPS position and plot the DR position at 1700 based on course 134° (per standard magnetic compass) and speed 10 knots, where does that put you on the chart? • When you compare that DR position with the actual GPS fix at 1700, in what true direction does the line from DR to fix point, and how long is that line in nautical miles?
• Be sure you are using true direction (°T) for the final set, not magnetic or compass course • Confirm the time interval (in hours) is correct before computing distance from speed • Measure the distance between DR and GPS fix accurately; divide by time in hours to obtain drift in knots
No comments yet
Be the first to share your thoughts!