Celestial Exercise for Part 16: Deviating your compass
15 November 2021 · 14 min · 754 views · Atlantic Ocean
What this video covers
Calculating compass deviation requires comparing the sun’s true azimuth to the shadow cast on the compass card. To perform this check, note the boat's current heading and the compass bearing of the shadow cast by the sun.3:52 Obtain the sun’s true azimuth (Zn) from a nautical almanac or calculation software.5:18 Determine the reciprocal of the azimuth by adding or subtracting 180 degrees.5:44 Apply the local magnetic variation to the true azimuth to find the magnetic bearing.9:20 The difference between this magnetic bearing and the observed compass shadow represents the compass deviation for that specific heading.9:55 Using the mnemonic "True Virgins Make Dull Companions" (True + Variation = Magnetic + Deviation = Compass), calculate the deviation by accounting for whether the variation is easterly or westerly.7:12 This process allows sailors to build a deviation table over time by recording results across various headings.3:21 The deviation remains constant for a specific heading regardless of the sun's position.13:12
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