On 8 February your 0800 zone time (ZT) position was LAT 28° 55.0' S, LONG 52° 27.0' W. Your vessel was steaming on course 036° T at a speed of 19.0 knots. An observation of the Sun's lower limb was made at 0938 ZT. The chronometer read 12h 37m 23s and was slow 01m 24s. The observed altitude (Ho) was 45° 29.2'. Local Apparent Noon (LAN) occurred at 1240 ZT. The observed altitude (Ho) was 77° 10.5'. What was the longitude of your 1200 ZT running fix?
• Run the AM sun line forward from the 0938 ZT sight to 1200 ZT using course and speed to obtain a running fix with the LAN line • Use LAN sight to get a good latitude and a meridian (north–south) line of position at 1240 ZT, then adjust it back to 1200 ZT by running it aft • For the AM sight, carefully convert chronometer time to GMT, then to Local Hour Angle (LHA) to ensure the azimuth and intercept are based on the correct time
• How many minutes of run are there between the 0938 ZT sight and 1200 ZT, and what is the corresponding distance and track made good along 036°T? • What is the time difference between your ZT LAN (1240) and 1200 ZT, and how far does the vessel move in that interval along 036°T? • Once both LOPs are transferred to 1200 ZT, where do they intersect relative to your DR position, and how does that intersection affect the final longitude?
• Be sure you convert chronometer time to correct GMT using the given slow error (+1m24s), and use that for the AM sight only • Use speed = distance/time carefully: convert minutes of run to hours before multiplying by 19.0 knots • When plotting, confirm that the LAN LOP is nearly north–south and that the AM LOP orientation (from azimuth) looks reasonable before you take their intersection as the running fix
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