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Lab 17-1 ONLINE
LESSON
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Do take notes as we peruse through this
lesson…
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Azimuth and Distance
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An azimuth is a compass direction from one point to
another…
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To use azimuth…a reference point must
be established…
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The north pole of Planet Earth can be used as a reference point.
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Place a protractor on the surface of our planet.
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The “N” of the protractor matches the “N” of our planet…
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“N” stands for north!
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North is a reference on our planet.
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Now we can find an azimuth…
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From the middle of the protractor…where the blue star resides
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To the green star…is an azimuth…a compass direction.
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The azimuth is 35° true
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A back azimuth is just an azimuth in the
opposite direction…
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From the green star to the blue star…
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The back azimuth is 215° true
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Adding 180° to 35° produces a back azimuth of 215.
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RULE #346:
If an azimuth is 180° or less…then add 180
° for a back azimuth
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RULE#9999:
If an azimuth is 181 or more…then
subtract 180 for a back azimuth
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We can find azimuths using maps and
charts…
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A map or a chart is a small graphical
representation of the surface of the
planet…
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Maps represent
land…
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Charts represent the ocean…
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To find an azimuth on a map or chart… two
locations are needed…
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An origination point (A) and a destination
point (B)…
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A
B
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Mark 2 locations on the chart with a green dry erase marker…
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With a green dry erase marker draw a line between the 2
points……
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Place a protractor on the chart…
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Make sure that the protractor’s
north/south axis is aligned with the
north/south axis of the chart…
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The north/south axis of the protractor must
be parallel with the north/south axis of
the chart…
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Then read the azimuth…
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The azimuth is 120° true…
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Distances can be determined from
maps and charts…
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There is a distance scale on the San
Francisco Bay chart …it is located at the
top of the chart.
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scale
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The scale represents 2 nautical miles.
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scale
1 nautical mile (nm)
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scale
1 nautical mile (nm)
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scale
2 nautical miles (nm)
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With a ruler, measure the length of a 1
nautical mile segment of the distance
scale…
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The length should be about 9.2 cm
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Use this relationship…
1nm9.2 cm
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To determine the distance between two points on a
chart…
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Draw a line with a dry erase marker between 2
points…
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Then measure the line in centimeters…
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If the line is 29 cm… use the relationship…
1nm9.2 cm
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1nm9.2cm
x29cm
=
Solve for “X”…
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The distance on the chart is 3.2 (nautical
miles) nm
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Referring to page 5 of Lab 62, a metric distance can be
calculated…
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This same ratio is seen on the Metrics
at a Glance reference guide…
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Ask Bob for Lab 17-1Q questions
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END
L17-1
