At 0820 zone time on 10 April you depart Yokohama, LAT 35°27.0'N, LONG 139°39.0'E (ZD -9). You are bound for Honolulu, LAT 21°18.5'N, LONG 157°52.2'W (ZD +10) and you estimate your speed of advance at 17.5 knots. The distance is 3,397 miles. What is your estimated zone time of arrival at Honolulu?
• Time-Speed-Distance formula: Time = Distance ÷ Speed • Difference between departure and arrival zone descriptions (ZD -9 and ZD +10) • How to convert between local time, Greenwich Mean Time (GMT/UT), and another zone time when crossing many time zones
• First, ignore time zones and just find how many hours and minutes it will take to go 3,397 miles at 17.5 knots. What is that time, and what date and time (zone of departure) does that give you? • Once you have the arrival time in the departure zone (ZD -9), convert that to GMT/UT. Are you adding or subtracting the zone description to get GMT? • From GMT/UT, convert to the arrival zone (ZD +10). Again, think carefully: does going from GMT to a positive zone description mean you add or subtract? After applying that, what local date change results at Honolulu?
• Recompute the time of passage: confirm the division of 3,397 by 17.5 and convert any decimal hours to hours and minutes correctly • Be sure you are using the correct sign convention: ZD East is plus, ZD West is minus, and remember that GMT = Local Time + ZD (with proper signs) • After converting to Honolulu time, check whether your result is closer to 17 April or 18 April, and whether it is in the early morning, mid‑afternoon, or later based on the total travel time and the 19‑hour zone difference
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