Compass Errors by Sun

At 1540 LMT, on 14th August 1991, the officer of the watch of a vessel in position 27°18’S 038°47’W observed the sun to check compass errors,

He obtained the following bearing: 321.5°C, 303° G. If variation is 23°W find each of the following:

a) The gyro compass error.

b) The error of the magnetic compass.

c) The deviation in the direction of the ship’s head.

LMT = 15h 40m 00s

LIT (038°47’W) = 02h 35m 08s

GMT = 18h 15m 08s (14th august)

GHA of the sun for 18h = 088° 49.6′

Increment for 15m 08s = 003° 47.0′

GHA of the sun = 092° 36.6′

Long = (-) 038°47′ W

LHA of the sun = 53° 49.6′

Dec = 14° 21.2′ N

d corr. (-0.8)= (-) 0.2′

Dec = 14° 21′ N

Now,

A = tan lat / tan P = tan 27° 18′ / tan 53° 49.6′ = 0.37738 N

B = tan dec / sin P = tan 14° 21′ / sin 53° 49.6′ = 0.3169 N

C = A + B = 0.6943 N

tan AZ = 1 / c * cos lat = 1 / (0.6943 * cos 27° 18′)

AZ = N 58.3° W (IF LHA 0° – 180°, body W)

AZ = 301.7° (T)

We Know, C – D – M – V – T

321.5° – ? – ? – 23° – 301.7°

321.5° – ? – 324.7° – 23° W- 301.7°

321.5° – 3.2 E – 324.7° – 23°W – 301.7°

So, deviation is = 3.2° E

Compass error = 19.8 W

a) Gyro compass error = 303° – 301.7° = 1.3 (H)

b) Magnetic compass error = 19.8° W

c) Deviation = 3.2° E