At 1200 zone time on 10 October, you depart San Francisco, LAT 37°48.5'N, LONG 122°24.0'W (ZD +8). You are bound for Yokohama, LAT 35°27.0'N, LONG 139°39.0'E, and you estimate your speed of advance at 22 knots. The distance is 4,536 miles. What is your estimated zone time of arrival at Yokohama?
• Time-Speed-Distance relationship: Use ( \text{Time} = \frac{\text{Distance}}{\text{Speed}} ) to find sea time in hours and days. • Zone description (ZD) and time zones: Understand how to convert between departure ZD (+8) and destination ZD (Yokohama’s local zone). • Date Line / change of date: Consider whether you cross the International Date Line going from San Francisco to Yokohama and how that affects the calendar date.
• First, compute how many hours it will take to travel 4,536 miles at 22 knots, then convert that to days and hours. • Next, add that travel time to the departure zone time and date to get an initial ETA in the departure time zone. • Then adjust for the difference in zone descriptions between San Francisco and Yokohama, remembering that you are steaming westward across the Pacific and likely crossing the International Date Line.
• Be sure you use nautical miles and knots consistently when applying the time-speed-distance formula. • Verify the zone description for Yokohama (its standard time offset from UTC) and compare it with ZD +8 for San Francisco. • Carefully account for any date change when crossing the International Date Line so your final date matches the local time at Yokohama.
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