On 30 July, your 0200 zone time (ZD +4) DR...

Question 1 / 2066636eea28f7522a1c51ae05

Question 1 of 2066636eea28f7522a1c51ae05

On 30 July, your 0200 zone time (ZD +4) DR position is LAT 43°48'N, LONG 78°00 W. At that time, you observe Polaris bearing 008.7°psc. The chronometer time of the observation is 05h 58m 07s, and the chronometer is 0m 23s slow. The variation is 10.5°W. What is the deviation of the magnetic compass?

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🔍 Key Concepts

• Polaris sights and true bearing – how to get the true azimuth of Polaris from the Nautical Almanac tables for latitude, LHA Aries, and date • Compass error = variation + deviation – be clear which sign (E or W) is added or subtracted • Converting bearings – path: per ship’s compass (psc) → compass → magnetic → true, and the reverse

💭 Think About

• From the given DR position, date, and corrected chronometer time, how do you find the Local Hour Angle (LHA) of Aries and then use the Polaris tables to get a true azimuth? • Once you have the true azimuth, how do you compare it to the observed compass bearing to find total compass error (including sign)? • After you know the total compass error and the variation, how do you isolate just the deviation, again paying attention to E/W signs?

✅ Before You Answer

• Be sure the chronometer correction (slow vs fast) is applied in the correct direction before entering the Nautical Almanac • Make sure you apply zone description (ZD +4) correctly when relating zone time to Greenwich time • Track the E/W signs consistently when converting between true, magnetic, and compass directions and when combining variation and deviation

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Question 1 of 20

0.5°E

3.0°E

7.5°W

18.0°W

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Question 1 / 2066636eea28f7522a1c51ae05

Question 1 of 2066636eea28f7522a1c51ae05

Back

Question 1 of 20

66636eea28f7522a1c51ae05

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🔍 Key Concepts

💭 Think About

✅ Before You Answer

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