COMPASS WORK

Question 1

1. Sketch lines of magnetic force showing the earth’s magnetic field and how a compass needle indicates Magnetic North (3)

Answer 1

Question 2

2. Define Variation (2)

Answer 2

The angular difference between True North and the 1 Earth’s Magnetic North. Variation is named East or West of True North 1

Question 3

Calculate the variation in 2018 using the information from a compass rose copied below (3)

Answer 3

Question 4

Define Deviation (2)

Answer 4

The angular difference between Magnetic North and Compass North. Deviation is named East or West of Magnetic North 1

Question 5

5. What corrects for the ship’s hard iron component of error? (2)

Answer 5

Fore & Aft and Athwartships permanent magnets & 1 1⁄2
Vertical (Heeling) magnet 1⁄2

Question 6

6. List the correctors which correct for the ship’s soft iron component of error (2)

Answer 6

Kelvin spheres (guadrantal correctors) & Flinders Bar & 1 1⁄2
Vertical (Heeling) magnet 1⁄2

Question 7

7. In addition to soft iron and hard iron, what else can affect the magnetic compass needle onboard? (1)

Answer 7

Siting of electrical equipment too close to the binnacle

Question 8

8. What does a compass adjuster do? (2)

Answer 8

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

Question 9

9. What is the residual error after the compass has been ‘swung’ and what is it made up of? (3)

Answer 9

Compass 1 Error. Made up of Variatidn and deviatioh.

Question 10

10. List the steps In finding the error of the compass (4)

Answer 10

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.

Question 11

List the further steps necessary to check the deviation card Is correct for the ship’s head (4)

Answer 11

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

Question 12

Ashiponaheadingof231°CfindsthatthedeviationforeachofthefollowingbearingsIs21⁄2°W:103°C, 205°C & 271°C. Why Is the deviation not different for each one? (2)

Answer 12

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

Question 13

Summerise how a free gyroscope Is made into a gyrocompass (2)

Answer 13

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

Question 14

What additional error occurs due to the vessel’s motion over the earth’s surface, how is It corrected? (3)

Answer 14

Steaming error- course/latitude/speed error
Input of latitude and speed for automatic correction

Question 15

Other than using a transit to check a gyro error, what might we use? (2)

Answer 15

Rising and Setting bearings of the sun

Question 16

A vessel on a Gyro heading of 015 observes a transit abeam on a true bearing of 104. What is the gyro
error? (3)

Answer 16

Question 17

List two things which make good watchkeeping practice In keeping a check on compass performance (2)

Answer 17

Comparing compasses (Gyros & magnetic)
Taking a compass error

Question 18

C1. Why Deviation change with the ship head?

Question 19

13. Atransit(33l°T) Is found to be bearing 337°C. Find the Compass Error. (4)

If the variation is known to be 7 1⁄2° W also find the deviation.

Answer 19

Question 20

How do you correct permanent and induced magnetism?

Answer 20

• For permanent magnetism use permanent fore and aft, atwarthship and vertical magnets
• For induced (temporary) magnetism use soft iron: Kevin balls for horizontal induced magnetism) and the Flinders bar for vertical induced magnetism