Compass lrg

Grunt Productions 2007

Compasses Compasses

A brief by Lance GrindleyA brief by Lance Grindley


Gyro CompassesGyro Compasses

Seamanship BooksSeamanship Books

ManualsManuals

Makers GuidelinesMakers Guidelines

Course NotesCourse Notes

Navigational TextsNavigational Texts


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.


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


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.


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.


Alignment of RepeatsAlignment of Repeats

Correct Correct BearingBearing

Bearing Bearing LowLow


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.


Magnetic CompassMagnetic Compass


The Earth’s Magnetic The Earth’s Magnetic FieldField

North

Magnetic

Pole

Magnetic Equator


Magnetic DipMagnetic Dip

H

Z

HorizontalComponent

VerticalComponent

Line of Total Force

Angle of Dip


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


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


Effect of Earth’s MagnetismEffect of Earth’s MagnetismEarth’s Total Force in relation to vessel

Vertical Component

Fore and Aft Component

Athwartships Component


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.)


Changing Ship’s HeadChanging Ship’s Head

RED RED

RED

BLUEBLUE

BLUEInduced Magnetism Fore/Aft

Induced Magnetism Athwartships

Lines of Force - Earth’s Field


Any Questions?Any Questions?

Compass lrg

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