Transcript Slide 1

The Weekend Navigator
Basic Level I
Copyright 2008 Coast Guard Auxiliary Association, Inc.
Chapter 5: Planning With GPS
and Paper Charts
Chapter 5: Lesson Objectives
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Criteria for a safe course
Steps in pre-voyage planning
Plotting on a chart
Entering waypoints into your GPS
Planning and Paper Charts
• Make sure you use the latest version of the
charts for your area of operation!
Criteria for a Safe Course
• Determining safe depths
– Characteristics of your boat
– Characteristics of the seabed
• Sounding is measurement of the bottom
depth at a particular location
• Contour lines can be drawn for constant
depths
Criteria for a Safe Course
• All soundings are referenced to a standard
datum
– Mean lower low water (MLLW)
– Each sounding represents the shallowest water
for that particular location
Criteria for a Safe Course
• Draft is the measure of how far a boat’s keel or
drive unit extends below the waterline
Criteria for a Safe Course
• Determining an adequate safety margin
depends on:
– Type of seabed
– Likely sea conditions
– Characteristics and vulnerabilities of your boat
Criteria for a Safe Course
• Isolated hazards can be natural or manmade
– Outlying rocks (exposed, covered, covering)
– Wrecks
– Old pilings
Criteria for a Safe Course
• Shoals are the tops of underwater hills that
may lie along a line
• Main channels may run parallel to shoals
Criteria for a Safe Course
• Horizontal clearance provides adequate room
to steer around obstacles
• Intended path - ten times wider than GPS error
to either side (i.e. error of 50 feet for most
units)
– One-tenth of a minute of latitude is equivalent to
600 feet and can also be used
Criteria for a Safe Course
• Overhead clearance is the vertical clearance
between the water level and an overhead
object
– Bridges and overhead cables
• Make sure to include antennas, radar,
outriggers poles in your vertical clearance
calculations!
Criteria for a Safe Course
• Overhead clearances
– referenced to mean high water (MHW)
– or mean higher high water (MHHW)
Steps in Pre-voyage Planning
• First: Locate home port and ports to visit
• Second: Locate hazards
• Third: Plot straight line paths to points of
interest
• Fourth: Invent short names for connecting
waypoints
Steps in Pre-voyage Planning
• Fifth: Note any landmarks
• Sixth: Measure coordinates of each waypoint
• Seventh: Complete waypoint table and enter
into GPS
Steps in Pre-voyage Planning
Creating Routes
• Select waypoints in a particular sequence to
create a desired route
Plotting on a Chart
• Thoroughly annotate your paper charts with
the information stored in your GPS
• Summary of Plotting Lines
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Course lines
Range lines
Dead Reckoning (DR)
Bearing lines
Plotting a Course
• Draw straight line segments on the chart to
avoid obstacles
• Measure the coordinates of the end points of
each leg
Plotting a Course
• Course legs should labeled using navigation
conventions
– C for course followed by three digit direction
– M for magnetic
Example:
– A course of 3o should be labeled “C 003 M”
– Label is placed near the waypoint above the
course line
Plotting a Course
• Distance of a leg starts with the letter “D”
and then the distance
• Distance label is placed under the line and
near the center of the leg
• Example: “D 2.6”
Plotting a Course
• Remember: Waypoint coordinates are just
numbers until they are plotted on a chart!
Plotting a Course
• A reciprocal is the course you would steer
if you came from the exact opposite
direction
– To determine a reciprocal, either add 180o to a
course less than 180o or subtract 180o from a
course more than 180o
• The reciprocal course heading is noted at
the other end of each line
Plotting a Course
• Example Problems:
• What is the reciprocal of 043?
• What is the reciprocal of 187?
Plotting a Course
• The reciprocal for 043 would be 43o + 180o
= 223o
• The reciprocal for 187 would 187o – 180o =
007o
The Compass Rose
• Provides the chart’s fundamental reference
for magnetic directions
• Outer ring aligns with the chart grid of
latitude and longitude or true north
• Inner ring aligns with magnetic north
The Compass Rose
The Compass Rose
• Variation describes both the:
– Magnitude of the difference in degrees and
minutes between true and magnetic north
– Direction of the offset either east or west
• Includes the date used for the variation and
the annual change
Using the Chart Grid and
Protractor Plotting Tool
• It is easier to plot courses and bearing in
degrees magnetic instead of degrees true
• You should be able
to do both
Adding or Subtracting Local
Variation
• Add westerly variation to your true course
• Subtract easterly variation from your true
course
Adding or Subtracting Local
Variation
• Examples:
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Local variation =15o W
True course= 175
What is your magnetic course?
175 T + 15o W = 190 M
If local variation = 15o E
What is your magnetic course?
175 T– 15o E = 160 M
Correcting for Deviation
• Deviation
– compass error or the difference between your
compass and magnetic north
• Compass deviation is unique to each boat
while variation is consistent within a given
area
Correcting for Deviation
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T = True direction
V = Local variation
M = Magnetic direction
D = Deviation of the compass
C = Compass direction
Correcting for Deviation
• Converting from true to magnetic
– Add westerly variation and subtract easterly
variation
• Converting from magnetic to true
– Add easterly variation and subtract westerly
variation
Correcting for Deviation
• Converting from magnetic to compass
– Add westerly deviation and subtract easterly
variation
• Converting from compass to magnetic
– Add easterly deviation and subtract westerly
variation
Correcting for Deviation
• True and magnetic directions are used for
plotting
• Compass courses are used for steering the
boat and are not plotted
Copyright 2006 Coast Guard Auxiliary Association, Inc.
Plotting a Bearing
• A bearing is a line of position and represents
a line on which your boat is located
• The object, not your boat, is used as the
reference point,
Plotting a Bearing
• The bearing line is drawn:
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Toward the object
Direction of the bearing
Estimated location of your boat
Labeled with 24 hour clock (4 digits) above the
line and direction of bearing (3 digits) below
the line
Plotting a Range
• Plotted as straight dashed lines between
charted objects with the line extending to
the navigation area
• Bearing is placed on top of the line
• Water towers, church spires, and day
beacons may be used as ranges
Summary
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Criteria for a safe course
Steps in pre-voyage planning
Plotting on a chart
Entering waypoints into your GPS