3. Grunt Productions 2007
Gyro CompassesGyro Compasses
Using a Gyroscope or Ring Laser Gyro to
detect rotation about a defined axis, a gyro
compass uses a gravity reference to detect
the Earth’s rotation about its North/South
axis and hence define the direction of True
North.
4. Grunt Productions 2007
Gyro InputsGyro Inputs
►All gyro compasses require:All gyro compasses require:
►Speed inputSpeed input
►LatitudeLatitude
►Speed input corrects for errors causedSpeed input corrects for errors caused
by ship’s movementby ship’s movement
►Latitude input ensures that the gyro isLatitude input ensures that the gyro is
processed at the correct rate to counterprocessed at the correct rate to counter
the earth’s rotationthe earth’s rotation
5. Grunt Productions 2007
Gyro AlarmsGyro Alarms
►Silence audible alarmSilence audible alarm
►Identify which gyro compass isIdentify which gyro compass is
affectedaffected
►Use alternative heading referenceUse alternative heading reference
►Alert Master, engine room andAlert Master, engine room and
maintainer.maintainer.
6. Grunt Productions 2007
Compass ChecksCompass Checks
► Transit which should be sufficientlyTransit which should be sufficiently
sensitive (pre-planned duringsensitive (pre-planned during
pilotage).pilotage).
► Azimuth of heavenly body either atAzimuth of heavenly body either at
sunrise/set .sunrise/set .
► Bearing of distant object usually takenBearing of distant object usually taken
alongside from accurately fixed berth.alongside from accurately fixed berth.
► Reduction of a “cocked hat” - notReduction of a “cocked hat” - not
recommended.recommended.
8. Grunt Productions 2007
The Magnetic CompassThe Magnetic Compass
► Emergency heading reference in mostEmergency heading reference in most
vessels.vessels.
► Fitted in all vessels to conform asFitted in all vessels to conform as
closely as possible to SOLASclosely as possible to SOLAS
regulations.regulations.
► Compass must be rotating card type,Compass must be rotating card type,
not reliant on any power supply.not reliant on any power supply.
► Fitted remotely from the bridge,Fitted remotely from the bridge,
normally above bridge deck.normally above bridge deck.
12. Grunt Productions 2007
Factors AffectingFactors Affecting
MagnetismMagnetism
►Vibration (when lying in magneticVibration (when lying in magnetic
field)field)
►Temperature (acts like vibration)Temperature (acts like vibration)
►Rust (oxidisation reducesRust (oxidisation reduces
magnetism)magnetism)
►Presence of electrical currentPresence of electrical current
►Induction from magnetic fieldInduction from magnetic field
13. Grunt Productions 2007
Ship’s MagnetismShip’s Magnetism
►PermanentPermanent -- caused by vibration and heat duringcaused by vibration and heat during
building (varies with heading and latitude on building)building (varies with heading and latitude on building)
►Sub-permanentSub-permanent -- slowly changing. Acquired byslowly changing. Acquired by
intermediate iron when ship has been on steadyintermediate iron when ship has been on steady
headingheading
►InducedInduced -- constantly changingconstantly changing
►Forces acting on the compassForces acting on the compass
Earth’s magnetism (H) north seeking elementEarth’s magnetism (H) north seeking element
Ship’s permanent, sub-permanent and inducedShip’s permanent, sub-permanent and induced
magnetism causing DEVIATIONmagnetism causing DEVIATION
14. Grunt Productions 2007
Effect of Earth’s MagnetismEffect of Earth’s Magnetism
Earth’s Total Force in relation to vessel
Vertical
Component
Fore and Aft
Component
Athwartships
Component
15. Grunt Productions 2007
Occasions forOccasions for
AdjustmentAdjustment
► After a considerable change in magnetic latitudeAfter a considerable change in magnetic latitude
► After dry-dockingAfter dry-docking
► If any of the correctors have been disturbedIf any of the correctors have been disturbed
► After modifications/repairs to electronic equipmentAfter modifications/repairs to electronic equipment
► Before sea trials of a new shipBefore sea trials of a new ship
► Annually.Annually.
► After extensive structural alterationsAfter extensive structural alterations
► After collision or grounding.After collision or grounding.
► After carriage of strong magnetic cargo (Steel girders,After carriage of strong magnetic cargo (Steel girders,
iron ore, steel pipe.)iron ore, steel pipe.)
16. Grunt Productions 2007
Changing Ship’s HeadChanging Ship’s Head
RED
RED
RED
BLUE
BLUE
BLUE
Induced Magnetism
Fore/Aft
Induced Magnetism
Athwartships
Lines of Force - Earth’s Field
When north becomes south At remote periods in the past, north has been south and south north. The Earth's magnetic field has proved a fickle lodestone, if you take a long enough view.
The magnetic field reversals, and even the origin of the magnetic field itself, are among the most perplexing problems in geology. Einstein is said to have put the origin of the field as one of his all-time five unsolved problems in physics.
Today geophysicists are pretty sure they know where the field comes from. Although the Earth's core contains plentiful amounts of iron and nickel, both magnetic materials, it cannot be a permanent magnet because temperatures at the centre are far above those at which these metals lose their magnetism. The magnetic field must be caused by the combination of rotation of the core, and the fact that it can conduct electricity. Movement plus current creates a magnetic field.
The Earth's field is known to reverse every 220,000 years. The actual reversal would take place over a period of about 1,000 years and then remain in its reversed orientation for about 4,000 years.
What would happen if the real magnetic field flipped? Sticky times. The magnetic field helps protect the Earth from damaging radiation from the Sun, so being without it for 1000 years would not only make navigation tricky. It might also throw human survival into question. Fortunately there's no evidence that this is going to happen any time soon.
Angle of Dip
When the direction of the earth's magnetic field is compared with the local horizontal, the angle between this field and the horizontal component is known as the angle of dip.
