On 7 November your 0830 zone time position was LAT 27°36.0'N, LONG 162°19.0'W. Your vessel was steaming on course 289°T at a speed of 19.0 knots. An observation of the Sun's lower limb was made at 0945 ZT. The chronometer read 08h 43m 11s and was slow 01m 51s. The observed altitude (Ho) was 38°21.1'. Local Apparent Noon (LAN) occurred at 1138 zone time. The observed altitude (Ho) was 45°35.0'. What was the longitude of your 1200 zone time running fix?
• Running fix using a morning Sun line advanced to LAN • Using zone time vs. GMT (UT) and correcting chronometer error • Converting time difference to longitude difference based on 15° per hour of Earth rotation
• How do you find the drift in longitude between your 0830 DR position and your 1200 running fix using your course and speed? • What is the line of position (LOP) from the 0945 Sun sight, and how do you correctly advance it to 1200 along the ship’s track? • How does the difference between LAN time and 1200 ZT help you confirm your final longitude choice?
• Be sure you’re using corrected GMT (UT) from the chronometer, including the "slow" correction, before entering the Nautical Almanac. • Check that you advance both the morning LOP and the LAN position using the same course and speed to 1200 ZT. • Verify that your final longitude change matches the elapsed time × 15° per hour relationship and stays consistent with your DR track (west vs. east).
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