Checking compass

Question 1

How often shall we check our compass?

Answer 1

Before departure and Once per watch

Question 2

How do we check our compass?

Answer 2

Transit bearing
Amplitude of the sun
Azimuth of a heavenly body

Question 3

How do we check our compass using a transit? (Gyro)

Answer 3

1. Take an observed bearing of the transit bearing
2. Find the true bearing on the chart
3. Compare observed bearing to true bearing to find compass error

Question 4

How do we check our compass using a transit? (Magnetic compass)

Answer 4

1. Take an observed bearing of the transit bearing
2. Find the true bearing on the chart
3. Note ships heading
4. Do a TVMDC calculation to find deviation
5. Compare deviation calculated to deviation card to find compass error

Question 5

How do we check our compass using Amplitude of the sun?

Answer 5

1. Take an observed bearing of the sunrise/sunset half a diameter over the horizon
2. Find declination in the Nautical almanac
3. Find latitude from GPS
4. Go to Norries and use appropriate table to find true bearing
5. Compare observed bearing to true bearing to find compass error

Question 6

How do we check our compass using Azimuth of a heavenly body?

Answer 6

1. Take bearing of heavenly body on the hour
2. Find declination of heavenly body in Nautical almanac
3. Get greenwich hour angle from nautical almanac
4. Convert greenwich hour angle to local hour angle (add or subtract your longitude depending on east or west from London)
5. Enter rapid sight reduction table with your latitude (from gps), declination and local hour angle which will give you a Zenith value
6. Calculate true bearing from Zenith value
7. Compare true bearing to observed bearing and get compass error