On 1 April at 0515 zone time, morning stars were observed, and the vessel's position was determined to be LAT 27° 05.0' N, LONG 16° 30.0' W. Your vessel is steaming at 19.0 knots on a course of 022° T. A sextant observation of the Sun's lower limb is made at 0930 zone time. The chronometer reads 10h 28m 25s, and the sextant altitude is 46° 20.3'. The index error is 4.5' off the arc, and the chronometer error is 02m 15s slow. Your height of eye on the bridge is 57.0 feet. What is the azimuth (Zn) of this sight using the assumed position?
• Intercept (altitude) sight reduction using the assumed position from the DR at the time of the Sun sight • Correcting sextant altitude: index correction, dip, and total altitude corrections from tables to find Ho • Finding Zn (azimuth) from the sight reduction tables (e.g., HO 249/229) using L, dec, and LHA of the Sun
• How do you advance your 0515 morning star position to 0930 using the vessel’s course and speed to get the correct assumed position? • Once you have Hs, what are the exact correction steps (in order) to reach Ho, and which of these depend on height of eye and index error? • To get Zn, which angles from the sight reduction process (Hc, Z or Zc) are involved, and how do you convert that to a true azimuth bearing measured clockwise from true north?
• Verify the DR advancement from 0515 to 0930: correct time interval, speed in NM, and latitude/longitude change on course 022° T • Carefully apply index correction (off the arc vs. on the arc) and dip correction (using 57 ft eye height) in the correct sign to Hs before using any tables • Confirm you are using the correct quadrant and convention for Zn: 0°–360° measured from true north, and that you’ve converted any tabular Z or Zn correctly for the Sun’s position (morning vs. afternoon, N vs. S declination)
No comments yet
Be the first to share your thoughts!