Magnetism & Compass

Question 1

Examples of permanent magnetism?

Answer 1

The steel of which ship is built of. Hull, ships structure, bulkheads, cranes, engines, anchors

Question 2

Examples of electro magnetism?

Answer 2

Added machinery, speakers, instruments

Question 3

What is variation?

Answer 3

The angular difference between True north and Magnetic north

Question 4

When should the magnetic compass be adjusted? (5 Factors)

Answer 4

1. Every two years the compass must be swung and adjusted by a compass adjuster
2. When major yard work has been conducted which may have changed the permanent magnetism
3. If new equipment has been added
4. Damage has been done to the vessel
5. If a noticeable change has been seen

Question 5

What is deviation?

Answer 5

The angular difference between Magnetic north and Compass north

Question 6

What are permanent magnets used for?

Answer 6

To counteract ship’s permanent magnetism

Question 7

How do we counteract Induced magnetism?

Answer 7

Soft Iron
Horizontal magnetism = Kelvin balls
Vertical magnetism = Flinders bar

Question 8

Which solas chapter and annex is magnetic compasses?

Answer 8

Solas chapter 5. Annex 13

Question 9

Name some reasons for a change in deviation in the long term? (2 factors)

Answer 9

Refit period. If major works are undertaken causing vibrations to the hull.

Long voyages on repeated heading

Question 10

Reasons for a change in deviation in the short term? (4 factors)

Answer 10

1. Changes of electrical equipment.
   2 .Heavy shocks to vessel- pounding.
2. Lightning strikes
3. If lubber line is incorrectly aligned.

Question 11

What does a fluxgate compass do?

Answer 11

Detects the Earth’s magnetic field electronically.

Question 12

Advantages of fluxgate compass? (4 factors)

Answer 12

1. Small with no moving parts
2. Self correcting
3. Transmits data to other units.
4. Can be fitted anywhere.

Question 13

Disadvantages of a fluxgate compass? (2 factors)

Answer 13

1. Must remain horizontal so must be fitted with gimbals/ additional vertical correctors.
2. Requires power to drive the reference coils.

Question 14

What is induced magnetism?

Answer 14

The short temporary effect on the compass due the heading or temporary changes due to i.e cargo

Question 15

How do we counteract permanent magnetism? (3 factors)

Answer 15

Hardcore magnets
1. Heeling error corrector magnets on a pendulum
2. Fore-and-aft corrector magnets
3. Athwartship corrector magnets

Question 16

List places where we can find value of variation?

Answer 16

1. Compass rose adjusted for year
2. Interrogate ENC
3. Variation charts
4. Compass error

Question 17

When shall the OOW check the compass error?

Answer 17

Before departement and At least once every watch

Question 18

How does a gyroscope work?

Answer 18

Free spinning gyro allowed 3° of movement damped in tilt (immersed in gyro fluid) allows gyro to stay fixed to true north

Question 19

What gyro errors are there?

Answer 19

1. Speed error
   If the vessel accelerates or changes course aggressively this can cause the gyro to slightly deflect from its spin axis
2. Latitude error
   A deflection of the gyro off its spin axis depending on the latitude (and therefore how fast the earth is rotating beneath the vessel)

Question 20

Which input does an gyro have to improve accuracy?

Answer 20

GPS

Question 21

What is a Pelorus?

Answer 21

A method of taking bearings relative to ship’s head or to the compass via the brass wheel

Question 22

What is an Azimuth mirror?

Answer 22

Goes on top of the compass and lets us take bearings

Question 23

What are the operational- / pre departure- checks of a magnetic compass? (9)

Answer 23

Freedom of movement of the gimbal

Card floating freely and level, and rotating without any friction

Compass card clear and sharp with no distortion or discolouration

Liquid clear and free of bubbles

No liquid leaks around seals or filler plugs

Optical system adjusted and clean

Azimuth reading devices and means of illumination in working order

No tools or speakers close to the compass

The compass error log book and deviation card for each magnetic compass installed should be checked

Question 24

What are the operational-checks of a gyro compass? (8)

Answer 24

Calibration
Check for errors
Cleaning and lubrication
Power supply and backup
Mechanical alignment
Regular inspection
Routine testing
Record keeping

Question 25

What is on the deviation card? (9)

Answer 25

Location and date of swing

Name and CoC of adjuster
Name and CoC of Master
Name of Harbour Master

Location of all correctors

Residual Deviation

Flinders Bar

Heeling Magnets

Information to re-create the swing