On 30 August your 0554 zone time (ZT) position was LAT 25° 39.0' S, LONG 31° 51.0' E. Your vessel was steaming on course 325° T at a speed of 15.0 knots. An observation of the Sun's lower limb was made at 0836 ZT. The chronometer read 06h 38m 36s and was fast 02m 24s. The observed altitude (Ho) was 30° 49.2'. LAN occurred at 1157 ZT. The observed altitude (Ho) was 56° 40.0'. What was the longitude of your 1157 ZT running fix?
• Running fix using two Sun lines of position (LOPs) several hours apart • Using LAN (Local Apparent Noon) to find a meridian passage longitude line • Converting chronometer time to GMT (UT) and then to arc for longitude
• How does the Sun’s GHA at the time of the 0836 sight compare to its GHA at LAN, and what does that tell you about the ship’s east–west movement? • Once you find the longitude at LAN from the Sun’s meridian altitude, how do you advance or retire the earlier morning LOP to 1157 ZT using the DR track? • What is the total run (in distance and direction) between 0554 ZT and 1157 ZT, and how will that shift the earlier LOP to intersect with the LAN meridian line?
• Be sure you correct chronometer time to GMT correctly, including applying the chronometer error with the correct sign (fast vs slow). • Verify you are using the correct DR positions at each sight time (0836 ZT and 1157 ZT), not just the 0554 ZT position. • Check the sense of longitude change: with course 325° T and 15 kn, is your longitude increasing (going west) or decreasing (going east)? This will help you eliminate options that change the wrong way.
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