On 22 February your 0800 zone time position is LAT 24°16'S, LONG 95°37'E. Your vessel is on course 126°T at a speed of 14 knots. An observation of the Sun's lower limb is made at 0945 zone time. The chronometer reads 03h 47m 22s, and the chronometer error is 02m 37s fast. The observed altitude (Ho) is 57°02.1'. LAN occurs at 1148 zone time, and a meridian altitude of the Sun's lower limb is made. The observed meridian altitude (Ho) is 75°22.3'. Determine the vessel's 1200 zone time position.
• Dead reckoning (DR) position from 0800 to 1200 using course and speed • How to use a meridian altitude (LAN sight) to find latitude from the Sun • Using the time of a Sun sight (0945 ZT) and chronometer data to refine longitude or check DR
• From 0800 to 1200, how far does the vessel travel along course 126°T at 14 knots, and what will the DR latitude and longitude be at 1200 if there were no celestial corrections? • How does the observed meridian altitude at LAN help you adjust the DR latitude—does it make you farther from or closer to the equator, and by about how many minutes of arc? • Compare the longitude implied by the 0945 Sun sight and LAN time with the DR longitude: does the Sun crossing the meridian at 1148 ZT tell you whether your actual longitude is east or west of the assumed meridian used for zone time?
• Compute the time run from 0800 to 1200 and convert it correctly to hours for the DR run. • Check that the latitude from meridian altitude is consistent with being in the Southern Hemisphere and with the Sun’s declination on 22 February. • Verify whether the LAN time vs. zone meridian indicates a correction that makes your longitude more easterly or westerly, and select the option whose longitude matches both this correction and your DR track.
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