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Magnetic Compass Operation and Components
Operation
The operation of a magnetic compass is very simple and can be stated as
follows: "A small bar magnet freely suspended in the magnetic field of
Earth will always align itself parallel to the lines of force of that field and
thus will establish a direction."
Components
Use the following table, figure 2-6, and figure 2-7 to learn the parts of a
magnetic compass.
Part
Card
Bowl
Magnets
Gimbals
Binnacle
Function
The card is an aluminum disk graduated in degrees
from 0 to 359. It has a jeweled bearing that rides on a
hard, sharp pivot point.
The card is supported by the bowl. A lubbers line is
marked on the bowl and is used as visible index. The
bowl is filled with Varsol to dampen overswings by the
card. An expansion bellows in the lower bowl serves
to allow expansion of the liquid with temperature
changes.
Several bar magnets are used to correct and align the
compass.
The bowl has two pivots that rest in a metal ring,
which also has two pivots resting in the binnacle. This
arrangement (gimbals) permits the compass to remain
level despite the motion of the ship.
The binnacle serves
as a housing for the
compass. It is
made of a non-
magnetic material.
It also serves as a
housing for the
compasses
correctors:
magnets, flinders
bar, and quadrantal
spheres. A lighting
system is normally
Figure 2-6. Compass binnacle
installed.
2-7
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