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Navigation
NAU 102
Lesson 15
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Magnetic Compass
Basic Principle
Small magnets are placed under a
compass card.
The card is free to move and
aligns with the horizontalcomponent of the Earth’s
magnetic field.
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Magnetic Compass
Early Compasses
A lodestone placed on a chip of
wood, floating in a bowl of water.
Modern Compasses
Basically the same. Just more
parts!
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Marine Compasses
Many ships will have two compasses:
Standard Compass
Located on the centerline, away from
magnetic influences.
Directions stated as “per standardcompass” (psc)
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Marine Compasses
Many ships will have two compasses:
Steering Compass
Located near the helm console.
Directions stated as “per steeringcompass” (p stg c)
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Compass Components
Bowl
Contains and supports all other
compass components
Constructed of non-magnetic
materialGlass cover is secured with a Bezel
Ring.
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Bowl & Bezel Ring
Bowl
Bezel
Ring
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Compass Components
Lubber’s Line
Aligned with the centerline of
the vessel.
Indicates the compass heading ofthe vessel.
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Lubber’s Line
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Compass Components
Compass Card
Stays aligned with magnetic
meridians.
Usually graduated in 360° andcardinal and intercardinal points.
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Compass Card
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Compass Components
Directive Magnets
Two or more magnets, mountedunderneath the compass card.
Align the card with the magneticmeridian.
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Directive Magnets
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Compass Components
Pivot
Pin in bowl which supports the
compass card.
Compass card rotates on a jeweled bearing.
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Pivot
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Compass Components
Compass Fluid
Clear liquid, resistant to freezing.
Usually glycol or petroleum based.
Reduces friction and oscillations.
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Compass Components
Card Float or Air Chamber
Attached to the card.
Supports most of the weight of the
card.
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Compass Components
Expansion Bellows
Allow the fluid to expand and
contract with temperature.
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Pivot
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Mounting Components
The compass is mounted on gimbals.
Double, hinged rings of non-
magnetic material.
Allow the compass to remain level as
the ship rolls and pitches.
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Gimbals
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Mounting Components
Gimbaled compass is
mounted in a Binnacle.
Supports the compass.
Protects fromenvironment and
magnetic interference
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Binnacle Components
Cover (Hood)
Protects the compass from the
environment.
Spider Glass
Magnifying glass to enable reading of
the compass.
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Binnacle Components
Light
Enables the use of the compass at
night.
Correctors
Minimizes the effects of magnetic
interference (deviation).
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Correctors
Quadrantal Spheres
Soft Iron Spheres
Reduce deviation on
intercardinal
headings
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Correctors
Fore and Aft /
Athwartships Magnets
Reduce deviation on
cardinal headings
Magnets placed in
movable trays under
the compass
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Correctors
Heeling Magnet
Vertically
suspended
beneath the
compass.
Corrects compass errors caused by
rolling and pitching.
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Correctors
Compensates for induced
magnetism caused by verticalcomponent of force.
Flinders Bar
Soft iron contained in a tube on the
outside of the binnacle.
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Binnacle
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Introduction to Navigation
Questions?