Compass

Question 1

Name the parts of the Compass Binnacle and what magnets are permanent or induced…

Answer 1

Question 2

Define Variation…

Answer 2

The angle between a magnetic line of force and a geographic (true) meridian at any location on Earth

Question 3

What causes Variation to a Compass?

Answer 3

• Variation exists because the Earth’s magnetic & geographic poles are not co-located (not in the same place)
• Magnetic anomalies in the Earth’s crust also contribute

Question 4

Define Deviation…

Answer 4

The angle between the actual magnetic meridian and the north line on the compass card

Question 5

What causes Deviation to a Compass?

Answer 5

• Deviation is caused by interaction of the ship’s metallic structure and electrical systems with the Earth’s magnetic field

Question 6

Define “Soft” Iron…

Answer 6

Metals that quickly loses its magnetism and is then re-induced by another field - these are known as INDUCED magnets

Question 7

Define “Hard” Iron…

Answer 7

Metals that retain magnetism - these are known as PERMANENT magnets

Question 8

Define “Angle of Dip”…

Answer 8

The angle in which the Earth’s magnetic flux hits a specific point on the Earth

Question 9

How does a ship gain its magnetic characteristics?

Answer 9

It is during the construction phase:
1. Banging metal together
2. Welding metal together (electric conductivity)
3. The ship’s heading in the yard

Question 10

How many component deviations of magnetism are there that will effect the Compass?

Answer 10

There are 5, which are known as Coefficients, conveniently named:
1. Coefficient A
2. Coefficient B
3. Coefficient C
4. Coefficient D
5. Coefficient E

Question 11

How many types of deviation caused by coefficients are there?

Answer 11

There are 3:
1. Constant
2. Semicircular
3. Quadrantal

Question 12

Define “Constant” Deviation…

Answer 12

A deviation of same sign and value at ALL headings

Question 13

Define “Semicircular” Deviation…

Answer 13

Deviation of the same sign for one continuous half of the compass courses and of the opposite sign for the other continuous half of the compass courses

Question 14

Define “Quadrantal” Deviation…

Answer 14

Deviation of one sign over continuous opposite quarters of the ship’s head and of opposite sign over the other two continuous quarters of the ship’s heading

Question 15

Describe Coefficient “A” on a compass (cause, type of deviation created, corrected?)…

Answer 15

CAUSE = unsymmetrical soft iron
DEVIATION = constant deviation
CORRECTED? = no, this coefficient CANNOT be corrected

Question 16

Describe Coefficient “B” on a compass (cause, type of deviation created, corrected?)…

Answer 16

CAUSE = permanent magnetism in fore & aft plane
DEVIATION = semi-circular (max = East & West)
CORRECTED? = corrected by the fore & aft magnets

Question 17

Describe Coefficient “C” on a compass (cause, type of deviation created, corrected?)…

Answer 17

CAUSE = permanent magnetism in athwartships plane
DEVIATION = semi-circular (max = North & South)
CORRECTED? = corrected by athwartship magnets

Question 18

Describe Coefficient “D” on a compass (cause, type of deviation created, corrected?)…

Answer 18

CAUSE = symmetrical soft iron in the horizontal plane
DEVIATION = quadrantal (max = NE, SE, SW, NW)
CORRECTED? = by Kelvin Balls / corrector spheres

Question 19

Describe Coefficient “E” on a compass (cause, type of deviation created, corrected?)…

Answer 19

CAUSE = asymmetrical soft iron
DEVIATION = quadrantal (max = N, E, S & W)
CORRECTED? = no, this coefficient CANNOT be corrected