Transcript Slide 1

The Weekend Navigator
Basic Level I
Copyright 2008 Coast Guard Auxiliary Association, Inc.
Chapter 4: The Tools of
Navigation
Chapter 4: Lesson Objectives
• Charts and their construction
• Mercator projection versus a polyconic
projection
• Pros and cons of Mercator projections
• Pros and cons of polyconic projections
• Reading a chart
Chapter 4: Lesson Objectives
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Navigational tools
Using navigational tools
Using other navigational tools
Lesson experience using plotting
exercises
What are the Tools of the Trade?
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Charts
Aids to navigation
Plotting tools
Compasses
Electronic navigation
instruments
What is a Nautical Chart?
• Provides information what is on and under
the water
• Scaled representation of the earth,
accurately portraying shapes, distances, and
directions
• Charts are made to be drawn on!
Who Prepares Nautical Charts?
• Information is provided by the National
Oceanographic and Atmospheric
Administration (NOAA)
• Charts are prepared by the National Ocean
Service (NOS)
How to Project the Earth on a
Flat Chart?
• Done by using projections for specific
applications
• Two types of maps:
– Mercator projections
– Polyconic projections
Mercator Projection?
• Parallels of latitude are horizontal and
straight
• Meridians of longitude are vertical and
straight
• Parallels intersect the meridians at right
angles
Advantages of a Mercator
Projection
• You can measure and plot directions and
distance directly on the chart and use them
for navigation
• Maintains directional relationships better
over long distances
• Projection of choice for coastal and offshore
navigation
Disadvantages of a Mercator
Projection
• Distorts the shapes and relative sizes of
landmasses and ocean basins
– Land masses will appear larger than they
actually are
• Distortion becomes exaggerated near the
poles
Polyconic Projection
• Developed from a series of cones placed
over the earth’s surface and then flattened
• In local areas, the parallels are
perpendicular with the meridian
• Courses can be plotted
Polyconic Projection
Polyconic Projection
Advantages of a Polyconic
Projection
• Used for inland and lake nautical charts
– Great Lakes and major river systems
Disadvantages of a Polyconic
Projection
• Not suitable for plotting travel over great
distances
What Information is Found on a
Chart?
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Depths
Scales
Updates
Coordinates
Symbols
Chart grid
Horizontal datum
Depths
• Soundings are plotted depth measurements
either in feet or fathoms
• Vertical datum or standard is established
because of fluctuating water levels in tidal
regions
– Mean low water (MLW)
– Mean lower low water (MLLW)
Depths
• Depth contour lines are used to identify
points of selected constant depth
– Plotted in multiples of fathoms (6 feet)
– Contour depths are oriented with the contour
and is in contrasting print (italic vs. regular)
Depths
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Shallow water is colored light blue
Deep water is colored white
Very shallow water is colored green
Land is colored tan
Scales
• Charts come in variety of scales
– 1:40,000-scale means 1 inch on the chart
equals 40,000 inches (1/2 nautical mile)
• Local waters: 1:20,000 scale
• Harbors: 1:10,000 scale
• Open waters: 1:80,000 scale
Scales
• The smaller the ratio, the larger the scale
and the more detail (i.e. 1:10,000)
– Good for navigation in narrow and rock-strewn
waters
• The larger the ratio the smaller the scale and
the less detail (i.e. 1:80,000)
– Good for “big picture” cruise planning
Updates
• Updated only at intervals
• Updates provided by hydrographic via
Notice to Mariners (NTM)
• Updates provided by the USCG via Local
Notice to Mariners (LNM)
Chart Grid and Horizontal Datum
• Utilizes a system of coordinates of latitude and
longitude
• Horizontal datum is a framework that allows for a
common reference
• World Geodetic System 1984 (WGS-84) is used
today as the horizontal datum
Coordinates
• Latitude and longitude provide a nautical
position address
• Latitude scale is found on the left and right
margins of the chart
• Longitude scale is found on the top and
bottom margins
Coordinates
• Meridians are lines of longitude or vertical
slices that pass through both poles
• Prime Meridian is at 0o and passes through
Greenwich, England
• All meridians are great circles
What is a Great Circle?
• An imaginary line scribed on the Earth’s
surface by a plane passing through the
exact center of the Earth
Rhumb Line
• Rhumb line is a course on a single bearing
Finding Your Spot on the Earth
• Scales on coastal nautical charts are
divided into:
– Degrees
– Minutes
– Tenths of minutes
• A minute of angle is 1/60th of a degree
Finding Your Spot on the Earth
• A minute of latitude is always exactly equal
to one nautical mile
• The latitude scale can be used for measuring
distance on the a chart
• A minute of longitude is equal to one
nautical mile only at the equator, but can
not be used for measuring distance on a
chart
Chart Symbology
• Rocks
• Wrecks
• Other obstacles
Navigation Aids
• Lateral aids or marks indicate the sides and
center of the channel
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“Red right returning” rule of lateral marking
Safe water or mid channel marks
Day beacons
Lighted beacons
Navigation Aids
• Informational aids mark dangers or note
local rules
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No-wake zones
Barge moorings
Anchorage areas
Wing dams on rivers
Rocky areas
Swimming beaches
Day Beacons
• Day beacons are unlighted fixed navigation
aids
– Indicated on a chart by a green square or red
triangle
– May be on land or in shallow waters on poles
Lighted Beacons
• Lighted fixed navigation aid indicated
on a chart by a symbol that resembles an
exclamation mark
– Solid black dot indicates
actual position
– Magenta teardrop flare indicates
it is lighted
Characteristics of Lighted
Beacons
• Characteristics are printed next to the
symbol
– Pattern of “4s” mean 4 second intervals
– Colors of “R” (red), “G” (green), “Y” (yellow),
and “W” (white)
– Height of the aid
– Visible range of the aid
Light Patterns
• Certain navigational aids have prescribed
light patterns
• Lighted center channel buoy flashes a
Morse code “A” (short-long) pattern with
white light
• Junction buoy will flash a two short plus
one short (2+1) pattern either red or green
Buoys
• Buoys have a small, open, black circle with
a diamond flare
• Color of the buoy is given in the label
– “R” = red, “G” = green, “RW” = red/white
Buoys
• Nun buoy (“N”) is conical is shape and red
in color
• Can buoy (“C”) is cylindrical and green in
color
• Mid channel buoy has red/white vertical
stripes and a white light
Other Buoys
• Sound-making buoys
– Bell buoys
– Gong buoys
– Siren buoys
• Light colors may be red, green, or
white
Plotting Tools
• Dividers
• Parallel rules
• Protractor
• Tool kit
Dividers
• Used to measure distances
• Used to measure latitude and longitude
coordinates
• Drawing compass is similar to dividers
Determining Latitude Coordinate
• One point is placed on spot of interest and
other point is on a line of latitude
• Divider is transferred to latitude scale
– Read as degrees, minutes, and 1/10ths of minutes
north (N)
Measuring Distance Using
Dividers
• One point is placed on each end of the
distance
• Divider is transferred to distance scale to
determine the distance measurement
Measuring Distance Using
Dividers
• Remember: Most charts have distance
scales in nautical miles, statute miles, and
kilometers. On the water, use nautical
miles because of the natural relationship
with latitude
Measuring Distance Using
Dividers
• Distance longer than dividers?
– “walk” your dividers along the distance line
Parallel Rules
• Consists of a pair rules joined by two or more
swinging hinges
• Serve as a straight edge for plotting
• Helps transfer a
plotted bearing line
across the chart to
compass rose
Rolling Parallel Rules
• One straight edge
• Moves across the chart on a long roller
Protractor Plotting Tool
• Easier to use than parallel rules particularly
in cramped spaces
Navigation Tool Kit
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Drawing compass
Calculator
Notebook
Pencils/erasers
Waterproof sleeves for charts
Other Navigation Tools
• Ship’s compass
• Hand bearing compass
• Global Positioning System
(GPS)
• Other electronics
The Ship’s Compass
• Every boat should have a compass.
• Quality and size are important
• Deviation must be adjusted for and done
by a professional
Hand Bearing Compass
• A handheld magnetic compass with a built
in sight
• Used to take visual bearings
• Always use the compass from a single
spot near the helm
Global Positioning System (GPS)
• Most popular electronic navigation system
• Must have a clear view of the sky above
the boat and be able to receive
simultaneous satellite signals
• Remember: A GPS position
is just an abstraction until it
is plotted on a chart!
Other Electronic Devices
• Radar
– Powerful and versatile tool for fixing
positions using bearings and ranges
– Only electronic device for tracking other
vessels
• Depth sounder
– Tells the depth of water directly under your
boat
– Useful to compare depth readings with chart
soundings
Other Electronic Devices
• Fluxgate compass
– Helps eliminate potential errors caused by
friction of compass card
– Self-compensate for local magnetic variation
• Autopilot
– Mechanical device that controls the boat’s
rudder
– Must be connected to a fluxgate compass or
GPS device
Other Electronic Devices
• VHF radio
– Valuable tool especially in
emergencies
– New radios include a
digital selective calling
(DSC) function
– DSC transmits your
position when a call is
made
– Assists the USCG in
determining your position
Summary
• Nautical charts
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Depths
Scales
Updates
Chart grid
Horizontal datum
Coordinates
Symbology
Summary
• Navaids
– Beacons
– Buoys
• Plotting tools
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Dividers
Parallel rules
Protractor
Tool kit
• Compasses
– Ship’s compass
– Hand bearing compass
• Other navigation tools
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GPS
Radar
Depth sounder
Fluxgate compass
Auto pilot
VHF radio