Compass work

Question 1

Define variation

Answer 1

The angular difference between True North and the earths magnetic North. Named for East and West of True North

Question 2

Define Deviation

Answer 2

The angular difference between magnetic North and Compass North. Affected by materials such as metal and electrical components on board ship, as well as the heading of the vessel . Named East or West of Magnetic North

Question 3

What IS a magnetic compass?

Answer 3

A bar magnet freely suspended in the horizontal plane and acted upon by both the Earth’s Magnetic field and the magnetic properties of the ship

Question 4

What corrects for Ships hard iron component of error?

Answer 4

Fore/aft and Athwartships, permanent magnets

vertical (Heeling) Magnet (hard/soft iron)

All of these are inside the Binnacle, used for the Hard iron (permanent)

Question 5

What corrects for ships soft iron component of error?

Answer 5

Soft iron Spheres, or Kelvin spheres (quadrantal correctors)

Flinders Bar

Both are on the outside of the Binnacle

Question 6

What does a compass adjuster do

Answer 6

Swings the ship around a 360 degree arc of the horizon, whilst taking observations.
As they do this, they adjust the correctors and make notes of the whatever deviation they are unable to correct for. This is produced on a compass deviation card which is kept in the bridge by the Compass

Question 7

Residual error after compass has been swung, and what is it made of?

Answer 7

Compass error, Variation and Deviation

Question 8

Four steps in finding compass error

Answer 8

1. Take a compass bearing
2. Calculate the True Bearing
3. Find the difference between the two (Compass error)
4. Label it east if lower than T, West if higher than True

Question 9

Further steps necessary to check the deviation card is correct

Answer 9

1. Take an observation and note the ships head
2. Calculate and remove variation
3. Remove this from the compass error to find the observed deviation
4. Compare this with the DEV card for the same ships Head

Question 10

How is a free gyroscope made into a gyroscope?

Answer 10

It is gravity controlled to make it North Seeking
Then Damped to settle on the Meridian

Question 11

Steaming error with a gyro, What is it and How is this corrected?

Answer 11

Course/Latitude/Speed Error

Input of Latitude and speed for automatic correction

Question 12

Other than using a transit to check gyro error, what may we use?

Answer 12

Rising and setting bearings of the sun

Question 13

Two things which make for good watch keeping practice in keeping check on Compass performance

Answer 13

Comparing gyro and magnetic compasses

Taking Compass error

Question 14

What causes permanent magnetism?

Answer 14

Build material, direction, shape and size of hull

Question 15

What is, and what causes Induced magnetism?

Answer 15

Temporary effect on a magnetic compass due to the heading of the vessel in comparison to the earths magnetic field

Temporary additions of Ferrous materials (cargo)

Question 16

What causes electronic magnetism?

Answer 16

Bridge equipment, cabling, generators etc

A compass safe distance will be stated in the bridge equipment errors

0.6m as standard for yachts

Question 17

What is a Petal Diagram?

Answer 17

Rules
Red on the left side of the ship

blue on the right

Top block is red, deflected to the blue

Bottom block is blue, pointing north, deflected to the blue

East/West, no deviation, right to N

Arrows as the boat spins around, north facing point is deflected to the blue.

North and South have the Worst Deviation

Question 18

How often should we check our compass error?

Answer 18

At least once per watch

Or after a large alteration of course (20-30 degrees)

Coming into Port

Leaving Port

Question 19

How can we check compass error?

Answer 19

Transits

Azimuth calculation ( Any time you see a celestial body) Longer calculation

Amplitude of the sun
Can only be done twice a day (sunset and sunrise)
Quick and easy calculation

Question 20

What is declination?

Answer 20

The angle between the celestial and terrestrial equators
Always labelled North or south

Question 21

How does a GYRO work?

Answer 21

Gyroscopic inertia (rigidity in space) and the concept of Inertia

Question 22

What is found on a Compass Card?

Answer 22

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

Residual coefficients

Flinders Bar

Heeling Magnets

Information to re-create the swing

Question 23

Where do we find Variation?

Answer 23

Variation Charts
Standard Navigational Charts (SNC)
GPS screen
ECDIS

Question 24

In a magnetic Compass Binnacle, which magnets correct for Hard Iron (permanent magnetism)

Answer 24

Fore and aft magnets
Athwartships magnets

Heeling magnet (both Hard and Soft Iron)

Question 25

In a magnetic Compass Binnacle, which magnets correct for Soft Iron (Induced Magnetism)

Answer 25

Flinders Bar
Spheres (Kelvins Balls)

Heeling magnet (both soft and hard iron)

Question 26

What is retention error in a magnetic compass?

Answer 26

Error caused by a magnetic compass retaining some deviation after being on one heading for some while

Question 27

Operational (Departure) Checks of a Magnetic Compass

Answer 27

a) Freedom of Movement of the Gimbal

b) Card floating freely and level

c) Liquid free of bubbles and clear

d) Compass card clear and sharp, no distortion or discolouration

e) Optical system (if any) clean and adjusted

f) Azimuth reading devices and means of illumination in working order

g) No liquid leaks around seals or filler plugs

h) No tools, phones, equipment left near the binnacle

Question 28

What size vessels are required by SOLAS to carry a gyro compass?

Within what latitudes is a gyro compass reliable?

Answer 28

≥ 500gt

76° N - 76° S

Question 29

Under what Principle does a Gyro function?

Answer 29

Gyroscopic inertia, stabilising the gyro in space

It remains fixed to a position via precision

Question 30

How often must we check our compass deviation?

Answer 30

After every large alteration of course

Once per watch when there has been no major course alterations

Question 31

When must a magnetic compass be adjusted?

Answer 31

On instillation

When they become unreliable

Every 2 years

The ships undergoes structural repairs (damage etc)

When Electronic or magnetic equipment close to the compass is added, taken away or altered

Question 32

Regular Maintenance of a Gyro Compass

Answer 32

Regular Inspection

Calibration

Error Checks

Cleaning and Lubricating

Power supply and Backup power checked

Mechanical Alignment

Routine Testing

Record Keeping

Maintenance under the Manufacturers Guidelines

Question 33

What is a Pelorus?

Answer 33

An alternative to the Azimuth Mirror

Gives bearing relative to the Ships Head

Fitted on the bridge wing, with the locater key lining it up with the lubber line