On 19 September your 0300 zone time DR position is LAT 24° 35' N, LONG 88° 40' W. You are on course 288° T at a speed of 14 knots. You observed 3 celestial bodies. Determine the latitude and longitude of your 0600 running fix. ZONE OBSERVED BODY TIME GHA ALTITUDE (Ho) DECLINATION ------------------- -------- ------------- ------------ --------------- Regulus 0530 018° 56.5' 22° 45.2' N 12° 03.6' Sirius 0532 070° 12.2' 44° 30.6' S 16° 41.3' Hamal 0536 140° 44.1' 43° 16.5' N 23° 22.5'
• Dead reckoning (DR) track from 0300 to the times of each sight, then to 0600 • How a running fix uses Lines of Position (LOPs) advanced along track to a common time • Effect of course and speed (288° T at 14 knots) on both latitude and longitude over 3 hours
• First, compute the DR position at 0600 from the 0300 DR using course and speed. How far west and north should you have moved in 3 hours on 288° T at 14 knots? • Compare your approximate 0600 DR with each answer choice. Which options are clearly too far off track in latitude or longitude to be realistic? • Think about whether the running fix from 3 well-spread stars is likely to move you closer to, or farther from, the DR track—would it create a huge change in longitude or only a modest correction?
• Be sure you correctly convert 3 hours at 14 knots into distance run in nautical miles • Check the change in latitude and change in longitude implied by your DR run and by each answer choice; eliminate any that require an unrealistically large shift from DR • Verify that your chosen option lies reasonably close to the projected DR position at 0600, not far away from your expected track
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