NS310

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NS100
Fundamentals of Naval Science
Navigation Instrument
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Objectives
1. Know the capabilities of various instruments
used in piloting to determine direction, speed,
distance, and depth. 2. Know the capabilities
of various plotting instruments.
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Measurement of Direction
Azimuth Circle - A ring fitted over a gyro
repeater face for measuring the bearing to an
object. The necessary sights and mirrors for
shooting celestial bodies are mounted on the
circle.
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Measurement of Direction
Telescopic Alidade Identical to the az. circle,
but contains a telescopic sight for obtaining
bearings to navaids at greater distances.
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Measurement of Distance
Radar - Distance is obtained by a radio wave
that is transmitted into the air and returns as
an echo. The time interval between
transmission and return can be converted
into a physical range.
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Measurement of Distance
Stadimeter - Uses two logarithmic scales to
determine distance to objects of known height.
- The instrument is very accurate under 2000
yards, but gets progressively less accurate at
longer ranges.
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Stadimeter
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Measurement of Speed
Terms Speed over Ground - True speed, or
speed relative to the earth. Speed through
the water - Relative speed between the water
and the ship, not accounting for the effect of
current or seas.
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Measurement of Speed
Impeller Log - Measures a vessels speed
through the water by translating the rotation of
a small propeller or paddle wheel below the
water line into a measurement of fluid
speed. Pit Log - 3-foot long tube extended
beneath the keel to measure speed. The tube
measures static and dynamic pressure, and
translates the difference in pressure into a
measurement of speed.
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Measurement of Speed
Doppler Speed Log - Uses a transducer that
projects sonar beams to measure speed. By
measuring the Doppler shift, a measurement of
speed is determined. Shaft RPM - A graph a shaft
RPM vs. speed is produced by running a vessel
over a measured mile. This allows the
vessels speed to be estimated based on the
number of RPMs ordered.
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Measurement of Depth
Fathometer - Uses a transducer that transmits
a sonar pulse vertically in the water. The
fathometer computes the depth by measuring
the time interval from transmission of the
sound until the return of the echo.
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Piloting Instruments
Divider and Drawing Compass - Used to measure
distance on a nautical chart. Parallel
Ruler/Parallel Plotter/Parallel Motion Protractor
(PMP) - Used for plotting direction. Three-Arm
Protractor - Used to represent two horizontal
sextant angles on a chart.
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Review Questions
NONE
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Compliments of Curtis Senior High School NJROTC