Magnetic Compass and Gyrocompass

Question 1

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

Answer 1

Binnacle
- Made from non-ferrous material
- The casing which contains the magnetic compass
- Compass is mounted on gimbals which keep it level as the ship pitches and rolls

Kelvin Balls
- Corrects for F+A athwartship soft iron magnetism

Flinders Bar
- Soft Iron
- Correcting for funnel effect

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

Fore-aft Corrector Magnets
- Correct for F+A hard iron magnetism e.g ships hull

Athwartship Corrector Magnets
- Corrects for athwartship hard iron magnetism e.g. 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?
and
When should your magenetic compass 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 +/- 5° 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
• Check bulb

Question 8

How often should you take a compass error?

Answer 8

• Once a watch
• Any large alteration

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

Question 11

What is the Deflection error test and how does it work?

Answer 11

• A way of testing the compass for pivot friction
• Introduce a magnet to deflect the compass card. If the pivot is good then when you remove the magnet the card should return to and settle in its orginal position

Question 12

How does magnetism move around the Earth?

Answer 12

Goes in blue (North)
Comes out red (South)