Understanding and Calculating Compass Errors for MCA Orals Candidates
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Navigating the high seas accurately requires a thorough understanding of how to calculate compass errors and convert them to true bearings. This article will guide you through practical examples and easy methods to apply east and west variation, ensuring you're well-prepared for your MCA Orals.
Compass Error Calculation and Conversion to True Bearing
Understanding compass errors and converting bearings is fundamental for any maritime officer. Here’s a step-by-step breakdown with practical examples:
Example 1: Compass Error Calculation and Conversion to True Bearing
- Compass Bearing: 045°
- Variation (from chart): 5°E (East)
Calculation:
- True Bearing = Compass Bearing + Variation
- True Bearing = 045° + 5°E
- True Bearing = 050° (since variation is east, add it to the compass bearing)
So, the True Bearing is 050°.
Example 2: Compass Error Calculation
- True Bearing of an object: 120°
- Compass Bearing of the same object: 125°
- Variation: 3°W (West)
Calculation:
- Compass Error = True Bearing - Compass Bearing
- Compass Error = 120° - 125°
- Compass Error = -5°
Since the variation is west, it indicates that the compass bearing is greater than the true bearing, confirming the negative sign.
Example 3: Finding Compass Deviation
- True Bearing of an object: 080°
- Compass Bearing of the same object: 085°
- Variation (from chart): 2°E (East)
Calculation:
- Compass Error = True Bearing - Compass Bearing
- Compass Error = 080° - 085°
- Compass Error = -5°
- Account for Variation:
- Compass Error = Deviation + Variation
- -5° = Deviation + 2°E
- Deviation = -5° - 2°
- Deviation = -7°
So, the deviation on that heading is 7°W (West).
Applying Variation: East or West
A clear understanding of how to apply variation is essential for accurate navigation. Here’s an easy way to remember when to add or subtract variation:
Variation East (E):
- Mnemonic: "East is Least"
- Action: Subtract when going from true to compass; add when going from compass to true.
Variation West (W):
- Mnemonic: "West is Best"
- Action: Add when going from true to compass; subtract when going from compass to true.
Practical Examples
From Compass Bearing to True Bearing
- Compass Bearing: 030°
- Variation: 5°E
Calculation:
- East is Least: Add variation
- True Bearing = Compass Bearing + Variation
- True Bearing = 030° + 5°
- True Bearing = 035°
From True Bearing to Compass Bearing
- True Bearing: 090°
- Variation: 10°W
Calculation:
- West is Best: Subtract variation
- Compass Bearing = True Bearing - Variation
- Compass Bearing = 090° - 10°
- Compass Bearing = 080°
Tips to Remember
- "East is Least, West is Best":
- When converting to compass bearings, subtract east (least) and add west (best).
- When converting to true bearings, add east and subtract west.
- Charts and Deviation Cards:
- Always refer to the most updated nautical charts and deviation cards which indicate the current variation and any known deviations for accurate corrections.
- Practice:
- Regularly practice these conversions to become second nature. Use real-world examples and scenarios to reinforce learning.
By understanding and applying these principles, you can navigate safely and effectively, ensuring you are well-prepared for your MCA Orals. Remember, regular practice and reference to updated charts and deviation cards are key to mastering compass error calculations. Keep checking back as we update with new questions, answers, and resources to help you succeed. Happy sailing!