On 6 December your 0800 zone time DR position was LAT 21°48.0'N, LONG 124°30.0'E. Your vessel was steaming on course 045°T at a speed of 20.0 knots. An observation of the Sun's lower limb was made at 1012 ZT. The chronometer read 02h 10m 42s and was slow 01m 02s. The observed altitude (Ho) was 41°17.1'. LAN occurred at 1129 zone time. The observed altitude (Ho) was 44°53.7'. What was the longitude of your 1200 zone time running fix?
• Running fix using two Sun lines (morning sight + LAN) • Relationship between local apparent noon (LAN) time and longitude • Advancing a line of position (LOP) from the time of observation to 1200 using course and speed
• First, use the LAN time to think about what longitude the ship must be on when the Sun is on your meridian. How does the time of local apparent noon compare with zone time and Greenwich time? • Consider how far the vessel travels between 0800, the first sight (1012), LAN (1129) and 1200. How will that motion affect the position lines from each sight? • Ask yourself: which longitude choice best matches the longitude implied by LAN, after you account for vessel run and use the running fix concept?
• Be sure you have the correct chronometer time in GMT/UTC by applying the slow correction, then converting to zone time where needed. • Verify you use the correct zone description (ZD) for the longitude region around 124°–126°E. • Carefully compute the run between each event (0800→1012, 0800→1129, 0800→1200) using Speed = Distance / Time, and make sure you advance the proper LOP(s) to 1200 before choosing an answer.
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