Section 8: Principles of Magnetic Compass (Challenge Questions)

Question 1

Causes of sudden changes in deviation.

Answer 1

• Magnetic storms
• Local anomoly
• Cargoes

Question 2

If HE magnets are altered, would this effect other correctors and would correction hold good for all latitudes?

Answer 2

No, an overall compass adjustment would still need to be redone when changing latitudes significantly due to the changing vertical component of the Earth’s field.

Question 3

What would indicate the HE requires adjustment at sea?

Question 4

Name the various correctors and what is the function of each.

Answer 4

‘a’ rod always exists and is normally a ‘-a’ rod.
(continuous fore and aft soft iron beneath compass)

‘b’ rod does not normally exist in a symmetrically constructed vessel.

‘c’ rod will always exist and is normally a ‘-c’ rod.
(majority of soft iron aft and below compass)

‘d’ ‘f’ ‘h’ rods normally absent with symmetrically constructed vessel.

‘e’ rod always exists and is normally a ‘-e’ rod
(continuous athwartships soft iron beneath compass)

‘g’ rod always exists and if compass aft is a ‘+g’ rod.

‘k’ rod always exists and is normally a ‘+k’ rod

Note:
a, e, g rods are induced by H (vessel upright)
c and k rods are induced by Z (vessel upright)

Question 5

How would you make a adjustment of HE whilst at sea?

Answer 5

• Sights will usually be taken from the Bridge wing.
• Use the General Arrangment Plan to take measurement of the Bridge height from the water level.
• Refer to the Nautical Almanac and take the corresponding figure against the height measured.
• Apple the corrections necessary.

Question 6

How can you check the proper alignment of the lubber line?

Question 6

When would you have the compass adjusted?

Question 7

How would you detect or remoce permanent magneticm in the soft-iron correctors?

Question 8

How would you adjust the compass at sea by the use of the Sun?

Question 9

How is a bubble removed from the bowl. What fluid is used and what others fluid can be used?

Question 9

Spare compass bowl is shipped. Would you expect different deviations than before?

Answer 9

Yes.

Question 10

What is the cause of “HE” on east or west course?

Answer 10

Uncompensated “C” rod

Question 11

Can 1 sphere be filtered to the compass?

Question 11

How would you check the Azimuth Circle for inaccuracies?

Question 12

Use of the shadow pin.

Question 12

What is wrong with having large deviations?

Question 13

What is “Magnetic Safe Distance” for equipment and what does it mean?

Question 13

Can various tyes of cargo affect the compass?

Answer 13

Yes. Certain cargo have metal properties that could affect the magnetism of the vessel.

E.g. Iron

Question 14

What factors may cause the deviations to vary from predicted values?