At 0530 zone time on 20 December, you depart Cape Town (ZD -1). You are bound for New York (ZD +5), and you estimate your speed of advance at 25 knots. The distance is 6,762 miles. What is your estimated zone time of arrival at New York?
• Time-speed-distance relationship for sea passages • Converting elapsed time in hours into days and hours • Adjusting for difference in zone descriptions (ZD) between departure and arrival
• First, ignore time zones and figure out how many hours the passage will take at the given speed. Once you have total hours, convert that into days and hours and add it to the departure time and date in the departure zone. • After you get an estimated arrival in the departure time zone, then think about how the zone description changes from ZD -1 (departure) to ZD +5 (arrival). Which way does the clock move when you go to a larger ZD value? • Compare your final arrival date and time to the answer choices: are you off by a whole number of hours that might indicate a missed or reversed time-zone correction?
• Carefully compute time = distance ÷ speed in hours, and then convert hours to days + remaining hours. • Add the elapsed time to 0530, 20 December in ZD -1 before you do any time-zone change. • Apply the correct sign and direction when converting from ZD -1 to ZD +5; verify how many hours of difference this represents and whether you should add or subtract them.
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