Magnetic Compass and Gyrocompass

Question 1

What are the different parts of a magnetic compass and what do they correct?

Answer 1

Binnacle

• The casing which contains the magnetic compass
• Compass is mounted on gimbals which keep it level as the ship pitches and rolls

Kelvin Balls
- Correct for the errors of the flinders bar

Flinders Bar
- Correcting for vertical soft iron e.g. superstructure

Heeling Bucket
- Corrects for errors when the vessel heels, set vertically in a bucket beneath the compass

Fore-aft correcting magnets
- Correct for hard iron magnetism things like the ships hull

Question 2

What is Variation?

Answer 2

The difference between true north and magnetic north

Question 3

What is Deviation?

Answer 3

The difference between magnetic north and compass north

Question 4

What is a compass error?

Answer 4

The combination of the effect of variation and deviation

Question 5

What is the formula for working out a compass error?

Answer 5

True
Virgins
Make 
Dull
Company
At
Weddings

Question 6

When should your magnetic compass be adjusted?

When should it be performance checked?

Answer 6

• When first installed
• After a major refit
• Any electrical or magnetic equipment has been fitted near it
• Every two years as per planned maintenance
• If the magnetic compass becomes unreliable and differs a lot from the deviation card
• Ship has been laid up for a period of time

The performance should be checked (e.g do a compass error)

• After the ship has carried a cargo of magnetic properties
• Any electromagnetic equipment has been used to move cargo
• Ship has been in a collision

Question 7

What operational checks are there for a magnetic compass?

Answer 7

• gimbal moving freely
• Compass card clear, floating freely
• Liquid free of bubbles and clear, no leaks or broken seals

Question 8

How often should you take a compass error?

Answer 8

• Once a watch

- Any large alternation of course on watch

Question 9

What is on the back of a Deviation Card?

Answer 9

• Who, where and when was the last compass swing
• Time of next compass swing also in PMS
• Position of correcting magnets

Question 10

What checks do you do for a gyrocompass?

Answer 10

• Check if the gyro has displayed an error

- Check repeaters are in-line, should be <0.5° away from the gyro heading