On 19 June your vessel's 0523 ZT DR position is LAT 25° 12.0' N, LONG 123° 14.0' W, when an amplitude of the Sun is observed. The Sun's center is on the visible horizon and bears 052.0° per standard compass. Variation in the area is 15° E. The chronometer reads 01h 21m 58s and is 01m 18s slow. What is the deviation of the standard compass?
• Amplitude of the Sun for determining compass error (use Nautical Almanac tables for 19 June at your DR position) • Relationship between true bearing, magnetic bearing, compass bearing, variation, and deviation • Correcting a chronometer reading that is slow to get the correct GMT for entering the almanac
• How do you turn the observed standard compass bearing of the Sun into a true bearing using variation and deviation, and which of those is still unknown? • What steps are needed to find the true azimuth (amplitude) of the Sun at sunrise/sunset from the Nautical Almanac using latitude, declination, and LHA? • Once you have the true bearing from the almanac and your corrected GMT, how do you compare it with the observed compass bearing to solve for the unknown deviation?
• Be sure you apply the chronometer correction correctly: if it is slow, do you add or subtract to get correct GMT? • Confirm you are using the correct Sun declination and page in the Nautical Almanac for 19 June at the approximate GMT of observation • Track your signs carefully when converting between true, magnetic, and compass so that an E or W deviation comes out logically from your work
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