On 15 July in DR position LAT 22°19.0'N, LONG 154°37.0'W, you observe an amplitude of the Sun. The Sun's center is on the visible horizon and bears 298°psc. The chronometer reads 04h 45m 19s and is 01m 56s slow. Variation in the area is 7.5°W. What is the deviation of the standard magnetic compass?
• Amplitude of the Sun at the visible horizon (use the appropriate formula involving latitude and Sun’s declination) • Relationship between true bearing, variation, deviation, and compass bearing (TVMDC) • Correcting the chronometer time using its known error to get the right GMT for entering the Nautical Almanac
• How do you use the date and corrected GMT to find the Sun’s declination from the Nautical Almanac, and why is that declination essential for computing the Sun’s true amplitude? • Once you compute the true amplitude and convert it to a true bearing, how do you step through TVMDC to go from true bearing to compass bearing (or vice versa)? • Compare the computed magnetic bearing with the observed compass bearing: what does the difference tell you about the sign and size of the deviation?
• Be sure you corrected the chronometer time in the right direction using the 01m 56s slow error before entering the Nautical Almanac. • Confirm your amplitude calculation uses latitude and declination correctly (check whether you are taking the sine of the correct quantities and using the proper horizon formula). • When applying variation (7.5°W), verify your TVMDC sequence and the sign convention for deviation so that east/west deviation is not reversed.
No comments yet
Be the first to share your thoughts!