Download - Compass lrg
Grunt Productions 2007
Compasses Compasses
A brief by Lance GrindleyA brief by Lance Grindley
Grunt Productions 2007
Gyro CompassesGyro Compasses
Seamanship BooksSeamanship Books
ManualsManuals
Makers GuidelinesMakers Guidelines
Course NotesCourse Notes
Navigational TextsNavigational Texts
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.
Grunt Productions 2007
Gyro InputsGyro Inputs
►All gyro compasses require:All gyro compasses require:►Speed inputSpeed input►LatitudeLatitude►Speed input corrects for errors Speed input corrects for errors
caused by ship’s movementcaused by ship’s movement►Latitude input ensures that the Latitude input ensures that the
gyro is processed at the correct gyro is processed at the correct rate to counter the earth’s rotationrate to counter the earth’s rotation
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Gyro AlarmsGyro Alarms
►Silence audible alarmSilence audible alarm►Identify which gyro compass is Identify which gyro compass is
affectedaffected►Use alternative heading Use alternative heading
referencereference►Alert Master, engine room and Alert Master, engine room and
maintainer.maintainer.
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Compass ChecksCompass Checks
► Transit which should be sufficiently Transit which should be sufficiently sensitive (pre-planned during sensitive (pre-planned during pilotage).pilotage).
► Azimuth of heavenly body either at Azimuth of heavenly body either at sunrise/set .sunrise/set .
► Bearing of distant object usually Bearing of distant object usually taken alongside from accurately taken alongside from accurately fixed berth.fixed berth.
► Reduction of a “cocked hat” - not Reduction of a “cocked hat” - not recommended.recommended.
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Alignment of RepeatsAlignment of Repeats
Correct Correct BearingBearing
Bearing Bearing LowLow
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The Magnetic CompassThe Magnetic Compass
► Emergency heading reference in Emergency heading reference in most vessels.most vessels.
► Fitted in all vessels to conform as Fitted in all vessels to conform as closely as possible to SOLAS closely as possible to SOLAS regulations.regulations.
► Compass must be rotating card Compass must be rotating card type, not reliant on any power type, not reliant on any power supply.supply.
► Fitted remotely from the bridge, Fitted remotely from the bridge, normally above bridge deck. normally above bridge deck.
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Magnetic CompassMagnetic Compass
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The Earth’s Magnetic The Earth’s Magnetic FieldField
North
Magnetic
Pole
Magnetic Equator
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Magnetic DipMagnetic Dip
H
Z
HorizontalComponent
VerticalComponent
Line of Total Force
Angle of Dip
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Factors Affecting Factors Affecting MagnetismMagnetism
►Vibration (when lying in magnetic Vibration (when lying in magnetic field)field)
►Temperature (acts like vibration)Temperature (acts like vibration)►Rust (oxidisation reduces magnetism)Rust (oxidisation reduces magnetism)►Presence of electrical currentPresence of electrical current►Induction from magnetic fieldInduction from magnetic field
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Ship’s MagnetismShip’s Magnetism
►PermanentPermanent - - caused by vibration and heat during caused 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 by slowly changing. Acquired by intermediate iron when ship has been on steady intermediate iron when ship has been on steady headingheading
► Induced Induced - - 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 induced Ship’s permanent, sub-permanent and induced
magnetism causing DEVIATIONmagnetism causing DEVIATION
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Effect of Earth’s MagnetismEffect of Earth’s MagnetismEarth’s Total Force in relation to vessel
Vertical Component
Fore and Aft Component
Athwartships Component
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Occasions for Occasions 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 After carriage of strong magnetic cargo (Steel
girders, iron ore, steel pipe.)girders, iron ore, steel pipe.)
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Changing Ship’s HeadChanging Ship’s Head
RED RED
RED
BLUEBLUE
BLUEInduced Magnetism Fore/Aft
Induced Magnetism Athwartships
Lines of Force - Earth’s Field
Grunt Productions 2007
Any Questions?Any Questions?