# Compass work Flashcards

1
Q

Sketch lines of magnetic force showing the earth’s magnetic field and how a compass needle indicates Magnetic North

A
2
Q

Define Variation

A

The angular difference between True North and the Earth’s Magnetic
North. Variation is named East or West of True North

3
Q

Define Deviation

A

The angular difference between Magnetic North and Compass North. Deviation is named East or West of Magnetic North

4
Q

What corrects for the ship’s hard iron component of error?

A

Fore & Aft and Athwartships permanent magnets &
Vertical (Heeling) magnet

5
Q

List the correctors which correct for the ship’s soft iron component of error

A

Kelvin spheres (quadrantal correctors) & Flinders Bar &
Vertical (Heeling) magnet

6
Q

In addition to soft iron and hard iron, what else can affect the magnetic compass needle onboard?

A

Siting of electrical equipment too close to the binnacle

7
Q

What does a compass adjuster do?

A

He corrects the magnetic compass by swinging the ship and making observations and adjusting correctors. He then produces a Deviation card.

8
Q

What is the residual error after the compass has been ‘swung’ and what is it made up of?

A

Compass Error. Made up of Variation and deviation.

9
Q

List the steps in finding the error of the compass

A

Take a Compass bearing of something.

Calculate or find the True bearing.
Find the difference between the two, this is the error of the compass.

Label it East if lower than the True bearing or West if more.

10
Q

List the further steps necessary to check the deviation card is correct for the ship’s head

A

Take a Compass bearing of something.

Calculate or find the True bearing.
Find the difference between the two, this is the error of the compass.

Label it East if lower than the True bearing or West if more.

11
Q

List the further steps necessary to check the deviation card is correct for the ship’s head

A

At the same time as making the observation note the ship’s head.
From the chart calculate the Variation.

Remove this from the Compass Error to find the observed Deviation.

Compare this with the Deviation for the ship’s head on the Deviation Card

12
Q

A ship on a heading of 231oC finds that the deviation for each of the following bearings is 2½oW: 103oC,
205oC & 271oC.

Why is the deviation not different for each one?

A

The deviation is dependent on the ship’s heading, not bearings taken

13
Q

Summarize how a free gyroscope is made into a gyrocompass

A

It is gravity controlled to make it North seeking,
Then damped to settle on the meridian

14
Q
A