On 3 October your 2122 ZT position is LAT 26°32'N, LONG 84°26'W. You observe Polaris bearing 359.8°pgc. At the time of the observation the helmsman noted that he was heading 106°pgc and 107°psc. The variation is 0°. What is the deviation for that heading?
• Relationship between true, gyro, magnetic, and compass (psc) headings when variation is 0° • How Polaris is used to find gyro error (its true azimuth is very close to true north) • How to get deviation from the difference between magnetic heading and compass heading
• First, think about what the TRUE bearing of Polaris should be when you are in mid‑northern latitudes. How does that compare to your observed bearing of Polaris 359.8° per gyro compass (pgc)? What does that tell you about gyro error (E or W)? • Once you know the gyro error, apply it to the ship’s gyro heading 106°pgc to find the TRUE heading. With variation 0°, what does that make the magnetic heading? • Now compare the magnetic heading you just found with the standard compass heading 107°psc. Is the compass reading higher or lower than magnetic? Which way (E or W) must the deviation be to cause that relationship?
• Be clear on the sign convention: True = Gyro + (gyro error); decide whether you add or subtract based on whether the gyro is reading high or low. • Remember that with variation = 0°, TRUE and MAGNETIC are the same, so any remaining difference between magnetic and compass is deviation. • Double‑check whether a compass that reads more than magnetic corresponds to east or west deviation before choosing your answer.
No comments yet
Be the first to share your thoughts!