On 24 May your vessel's 1000 ZT position is LAT 25°36.0'N, LONG 118°39.5'W, when you take an azimuth of the Sun. Determine the gyro error using the azimuth information. Chronometer time: 06h 21m 48s Chronometer error: fast 01m 36s Gyro bearing: 099.4° Variation: 11.1°E
• Convert chronometer time to GMT (UTC) using the given chronometer error and determine the correct Greenwich Hour Angle (GHA) and declination of the Sun for 24 May at that exact time. • Convert gyro bearing to true bearing by correctly applying variation (and think about where deviation would come in if it were given). • Understand that gyro error = true heading − gyro heading (or equivalent relation) and be careful with the E/W sense of the error.
• Start by carefully correcting the chronometer time. Is the chronometer reading ahead of or behind GMT, and how does a fast error change the true GMT? • Once you have GMT, what sight reduction or almanac steps are needed to find the Sun’s true azimuth at your DR position and time? How does that compare to the observed gyro bearing? • When you compare the true azimuth to the gyro bearing, think: if the gyro compass is reading too far east or west of the true direction, which sign (E or W) does that give the gyro error?
• Be sure you have applied the chronometer error (fast/slow) in the correct direction before using almanac data. • Confirm that you converted the gyro bearing to true bearing using the correct rule for applying variation east (add/subtract?). • Before choosing an answer, check that your final gyro error sign (E or W) matches the logic of which way the gyro appears to be off when comparing true vs. gyro bearings.
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