Page 6
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The steering compass
The steering compass is a magnetic compass used to steer the
ship on a course that has been plotted from a chart. Two main
features include:
• A compass card that is graduated in 360 degrees mounted in
the bowl of a compass.
The card is a circle marked off in a clockwise direction in 360
equal units (360 degrees). North is marked at 0
O
, east at 90
O
,
south at 180
O
and west at 270
O
.
• A lubber line is a mark or projection on the compass bowl
whichallowthe skipper to sight the compass course calculated
from the chart (Figure 6.2).
Location
A steering compass will be fitted with corrector magnets to
compensate for errors caused by the magnetic fields in a ship.
A licensed compass technician will have set these up when the
compass was adjusted and are not interfered with.
It is installed on the centre line of the ship, high up, giving the
observer an unobstructed view.
It may be located on top of the bridge or wheelhouse with a
periscope to allow it to be read from the helm position.
Deviation errors
Erros occur due to the effect of Earth's magnetic field on the
ship’s individual magnetic field (see Figure 7.1 page over).
One error, called deviation, is corrected by creating a deviation
card (Figure 6.3). To do this the ship's compass is swung
around a known mark. It is then corrected by a set of magnets
as shown in Figure 6.4.
Figure 6.2 Steering compass and lubber line
Figure 6.3 Deviation table
Lubber line
Figure 6.4 Ships compass with correction magnets
Figure 6.1 A compass card
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Correction
magnets
Correction
magnets
Steering
compass
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