On 18 May your 1030 ZT DR position is LAT 20°41'N, LONG 63°32'W. You are on course 106°T, speed 24 knots. Determine your 1200 position using the following observations of the Sun. Zone Time GHA Declination Ho 1204 61°54.6' N 19°37.6' 88°39.7' 1210 63°24.6' N 19°37.7' 88°59.2'
• Running Fix with the Sun using two LOPs (lines of position) at different times • Converting Zone Time (ZT) to GMT/UT and then to Local Hour Angle (LHA) from GHA and longitude • Advancing or retarding an LOP using course, speed, and time run to get a running fix near 1200
• First, compute the time difference between each sight and 1200, then determine how far the vessel moves in that time on course 106°T. How will this distance be used on the LOPs? • Think about which LOP (1204 or 1210) needs to be ADVANCED to 1200 and which needs to be RETARDED to 1200 to form a running fix. How does your course direction affect this? • After plotting/advancing the LOPs, compare the resulting fix with the DR track from 1030. Which answer choice lies close to both the DR track and the intersection of your advanced/retarded LOPs?
• Make sure you use the correct sign for longitude when combining it with GHA to form LHA (west longitudes and GHA both increase westward). • Double-check the time interval in minutes (and thus distance run) between 1200 and each observation time; a small mistake here will shift your running fix noticeably. • Verify that your final position is consistent with the DR from 1030 to 1200 on course 106°T at 24 knots (it should not be unrealistically far off the track line).
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