Magnetic and Gyro compasses Flashcards
What is a magnetic compass?
A magnetic compass is used to provide an indication of direction and bearing in relation to magnetic north.
It is an important navigational aid as it can operate independently without electronic or electric input.
What is variation?
Variation is the difference between true north and magnetic north, caused by the earths magnetic field.
What is deviation?
Deviation is the difference between magnetic north and compass north, caused by the ships own magnetic field.
What is compass error?
Compass error is a combination of the effect of variation and deviation.
What is a binnacle of a magnetic compass?
A binnacle holds the compass and is mounted on gimbals to keep it level.
What are the spheres on a magnetic compass?
The flinder bar produces a small quantity of fore and aft and horizontal and vertical effect on the compass, the soft iron spheres correct these errors.
What is the heeling error on a magnetic compass?
Compensated by permanent magnets set vertically in a bucket beneath the compass.
What is the Flinders Bar on magnetic compass?
A soft iron vertical bar correcting for vertical soft iron abaft the compass (funnel).
What are the horizontal magnets on a magnetic compass?
Permanent fore and aft corrector magnets.
When should the magnetic compass be adjusted?
- When first installed
- If it becomes unreliable
- If ship has undergone any structural repairs or alterations
- If it has been more than 2 years since last adjustment
What operational check should be done on a magnetic compass?
- Check gimbal is moving freely
- Compass card is clear and sharp and floating freely
- Liquid free of bubbles
How should you monitor the performance of the magnetic compass?
- A compass error should be recored at least once a watch
- A compass error should be taken after every alteration of course
What is a gyro compass?
A gyro compass is a heading indicator that users the principles of a gyroscope in addition to the application of torque to ensure it automatically aligns to true north.
What are the advantages of gyro compass?
- A gyro compass finds true north
- A gyro compass is unaffected by ferromagnetic materials such as the ships hull
What checks would you carry out on a gyro compass?
- All repeaters should be within 0.5’ of the gyro compass
- A compass error should be taken at least once a watch
- When the vessel is on passage the gyro should be corrected for latitude and speed error
