Bridge Management - Ship's Compass Flashcards
Which SOLAS chapter and regulation and MGN details the carriage requirements for ships compass?
SOLAS chapter V, regulation 19 and MGN 610
What gross tonnage vessels are required to carry a gyro compass?
More than 500gt
When should the magnetic compass be adjusted? (5)
When the ship is built
The ship undergoes structural repairs/modification that could affect compass
Electronic equipment is added/removed that could affect the compass
The compass becomes unreliable
Every 2 years except when regular compass errors are taken
What is Variation?
Difference between Magnetic North and True North (Earth’s magnetic field)
What is Magnetic dip?
The angle that the earths field makes with the horizontal
What is Directive Force?
The desire of the compass needle to align itself with the earth’s magnetic field
What is Hard Iron (Permanent Magnetism)?
Not readily magnetised but will be permanently magnetised after magnetism influence removed
What is deviation?
Difference between Compass North and Magnetic North (Magnetic influence of the ship’s structure)
What is Soft Iron (Induced Magnetism)?
Readily magnetised but will lose magnetism after magnetism influence removed
What is Force P?
The fore and aft component of the ship’s permanent magnetism
What is Force Q?
The athwartships component of the ship’s permanent magnetism
What is Force R?
The vertical component of the ships permanent magnetism
What is the purpose of the binnacle?
Houses the ship’s compass
What is the binnacle made of?
Non-magnetic materials that will not corrode, traditionally wood and brass although contemporary binnacles made of fibreglass
Where is the binnacle located?
The vessels centreline, clear of sources of interference
Which way does the magnetic field run?
Out of the red and into the blue
What happens when two identical poles are offered up to one another?
They repel
What happens when two opposite poles are offered up to one another?
They attract
Where does the compass needle point to?
Magnetic North
What happens to H and Z at the magnetic equator?
Z is at it’s smallest, H is at its largest
What happens to H and Z at the magnetic poles?
Z is at it’s largest, H is at it’s smallest
What happens to directive force if H decreases?
Directive force will decrease
What happens to directive force if H increases?
Directive force will increase
What do we call it when directive force is weak?
Sloppy
Where is directive force the strongest and the compass therefore the steadiest?
Magnetic Equator
What happens to deviation as Latitude increases?
Deviation also increases
What is used to correct permanent magnetism (hard iron)?
Hard Iron Correctors (HIC) which are permanent magnets
What is used to correct induced magnetism (soft iron)?
Flinders bar and Spheres
How do you know if it is +P or -P?
+P is a blue bow, -P is a red bow
How do you know if it is +Q or -Q?
+Q is a blue starboard side. -Q is a red starboard side
When is a soft iron bar magnetised to its greatest extent?
When it lies North/South
What are the three types of soft iron onboard?
Vertical Soft Iron (VSI)
Fore & Aft Horizontal Soft Iron (HSI)
Athwartships Horizontal Soft Iron (HSI)
What component of the earth’s magnetic field is VSI induced by?
Vertical component of earth’s magnetic field (Z)
What component of the earth’s magnetic field is HSI induced by?
Horizontal component of earth’s magnetic field (H)
What is ‘a rod’?
Lie fore/aft, act fore/aft
What is ‘c rod’?
Lie vertical, act fore/aft
what is ‘e rod’?
Lie athwartships, act athwartships
What is ‘k rod’?
Lie vertical, act vertically
What causes coefficient B?
Force P and c rod
What causes coefficient C?
Force Q and f rod
What causes coefficient D?
a and e rod
What can be used to correct coefficient B?
Fore/aft magnets and flinders bar
What can be used to correct coefficient C?
Athwartships magnets and flinders bar
What can be used to correct coefficient D?
Spheres
On what heading would you correct Coefficient B?
East or West
On what heading would you correct Coefficient C?
North or South
On what heading would you correct Coefficient D?
Inter-cardinal headings
When is Coefficient D +D?
When it results in an easterly deviation when heading North East
When is Coefficient D -D?
When it results in an westerly deviation when heading North East
What is Heeling Error?
The difference between a vessel’s deviation when upright and when heeled on the same heading
What is used to correct Heeling Error?
Permanent vertical magnets
What is ship’s multiplier?
Difference between directional force at the ship’s position and the directional force ashore
What headings is heeling error maximum on?
North / South
What headings is heeling error zero on?
East / West
What is gyroscopic inertia?
The gyroscope resists any attempt to move it, it remains fixed in the rotor and axel whilst the gimbal frame moves around the gyro
What is azimuth?
The angle the axel makes with the meridian
What is altitude?
The angle the axis makes with the horizon
What is drift?
The change in azimuth, drifts east in northern hemisphere and west in southern hemisphere
Where is drift maximum?
The poles
Where is drift 0?
The equator
What is tilt?
The change in altitude, tilts upwards in east and downwards in west
What is tilt affected by?
Tilt is dependent on latitude, maximum at the equator, 0 at the poles. Tilt is also dependent on azimuth, maximum on E/W, 0 on N/S
