At 1830 zone time, on 6 April your DR position is LAT 26°33.0' N, LONG 64°31.0' W. You are steering course 082°T at a speed of 16.0 knots. You observed 3 celestial bodies. Determine the latitude and longitude of your 1900 running fix. Body Zone Time GHA Observed Declination Altitude Sirius 1836 73°02.7' 46°00.5' S 16°41.7' Regulus 1842 23°46.9' 49°07.2' N 12°03.5' Mirfak 1900 129°24.3' 35°50.5' N 49°47.7'
• Running fix with multiple bodies and advancing earlier LOPs (lines of position) to a common time • Use of DR (dead reckoning) track between 1830 and 1900 at a known course and speed to advance positions • Converting between zone time and GHA/LHA and plotting intercepts (toward/away) from the DR position
• How far (in miles) will the vessel travel from 1830 to each observation time and then to 1900, given the speed and course? • When you draw each celestial LOP at its observed time, in which direction and by how much do you advance it along the DR track to bring it to 1900? • Once the three advanced LOPs intersect near a common point, how does that plotted fix compare to the original DR position—does it end up slightly north/south and east/west of the DR?
• Compute and double-check the run from 1830 to each sight time and to 1900 using Speed = Distance / Time, including units and minutes of time. • Ensure the advancement of each LOP is applied along the correct course (082°T) and with the correct distance for the time difference between its sight time and 1900. • Verify that the final plotted fix lies close to the intersection of the three advanced LOPs and that the shift from the 1830 DR is reasonable for 30 minutes at 16 knots (about 8 NM).
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