On 12 April at 0515 ZT, morning stars were observed, and the vessel's position was determined to be LAT 21°05'S, LONG 16°30'W. Your vessel is steaming at 19 knots on a course of 278°T. A sextant observation of the Sun's lower limb is made at 0930 ZT. The chronometer reads 10h 28m 25s, and the sextant altitude (hs) is 40°15.9'. The index error is 2.5' off the arc, and the chronometer error is 2m 15s slow. Your height of eye on the bridge is 57 feet. What is the azimuth (Zn) and intercept (a) based on the assumed position of this sight?
• Time conversions between zone time (ZT), Greenwich Mean Time (GMT)/UTC, and chronometer time including chronometer error • Steps for reducing sextant altitude: applying index error, height of eye (dip), and main corrections to get observed altitude (Ho) • Using the assumed position, GHA/Dec of the Sun, and sight reduction tables (or formulas) to find computed altitude (Hc), intercept (a), and **azimuth (Zn)
• How do you correctly convert 0930 ZT to UTC using the zone description, and then apply the given chronometer error to find the exact time of observation? • Once you have sextant altitude (hs), what is the correct sign for index error "off the arc" and how does that, plus dip from height of eye 57 ft, affect the final Ho? • After finding Ho, Hc, and Zn from the assumed position, how do you decide if the intercept is toward (T) or away (A) the Sun based on Ho vs. Hc?
• Confirm the zone description (ZD) for longitude 16°30'W and ensure the ZT → UTC conversion is correct before using the Nautical Almanac data. • Carefully apply index correction: "off the arc" vs. "on the arc" changes the sign of the correction. • Verify whether Ho is greater or less than Hc; this alone determines whether the intercept is labeled T (toward) or A (away) in the answer choices.
No comments yet
Be the first to share your thoughts!