On 1 December your 1600 ZT DR position is LAT 22°48.0'S, LONG 91°26.0'E. You are on course 327°T at a speed of 16 knots. What will be the zone time of sunset at your vessel?
• Zone time (ZT) vs Greenwich Mean Time (GMT/UT) and how longitude affects time • How to use the Nautical Almanac daily pages and sunrise/sunset tables for the given date and latitude • Applying a longitude correction to convert from GMT to local zone time
• First, at the given DR position, what standard time zone (zone description, ZD) are you in based on your longitude? Is it east or west of Greenwich? • From the Nautical Almanac, what is the GHA/Dec or tabulated time of sunset on 1 December closest to LAT 23°S, and how do you interpolate for LAT 22°48.0'S if needed? • Once you have sunset in GMT at your longitude, how do you correctly apply the zone description (sign and size) to convert to zone time at the vessel?
• Be sure you have the correct zone description (ZD) for 91°26.0'E (check the 15° per hour rule and round correctly). • Confirm whether you must interpolate for latitude or if a single tabulated value is close enough for exam purposes. • Double-check the sign when converting from GMT to ZT: ZT = GMT ± ZD (are you adding or subtracting for east longitude?).
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