At 0915 zone time on 6 March you depart Sydney, LAT 33°51.5'S, LONG 151°13.0'E (ZD -10). You are bound for Kodiak, LAT 57°47.0'N, LONG 152°25.0'W, and you estimate your speed of advance at 21 knots. The distance is 6,222 miles. What is your estimated zone time of arrival at Kodiak?
• Time = Distance ÷ Speed to get total travel time in hours and days • Converting between zone time (ZT) and Greenwich Mean Time (GMT/UTC) using zone descriptions (ZD), including sign conventions • Handling change of date when crossing the 180° meridian and moving from East longitudes to West longitudes
• First, compute how many days and hours it will take to travel 6,222 miles at 21 knots. What is that total time, in days and hours? • Convert the departure ZT (Sydney, ZD -10) to GMT at the moment of departure. Then add the travel time to get the GMT of arrival. • Determine the correct ZD for Kodiak from its longitude, paying attention to the sign (East vs West). Then convert your arrival GMT to arrival ZT, and carefully account for any date changes when you cross the 180° meridian.
• Be sure your time = distance ÷ speed calculation is done with knots (nm/hr) and miles in the same units • Double-check the sign of each ZD: East longitudes are generally negative ZD, West longitudes positive ZD in traditional nautical problems • After converting back to ZT at Kodiak, verify the calendar date: did you move into the next day or back into the previous day when applying the time-zone and date-line effects?
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