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Advanced Piloting Course
Chapter 4Avoidance Techniques
United States Power Squadrons ®
Slide 2
Navigation from a different Perspective
What you have learned:• Point-to-point navigation
Primary technique in Piloting & AP Pre-qualify the path, follow the path
Alternative & complementary approach• Navigating to avoid
Avoid shallow water Avoid hazards Avoid restricted areas
• Chapter 4 Danger Bearings, Circles Avoidance Techniques
Slide 3
First Step
Determining what to avoid• Examine chart for region of interest• Identify:
Region for boating» Limits of latitude and longitude» Harbors or bays
Hazards» Rocks» Obstacles» Shallow water
Charted, visible reference points» Navigation aids» Landmarks
© 2003, R J Sweet, “GPS for Mariners.” Reprinted with permission© 2004 “The Weekend Navigator”
Slide 4
Determining the Avoidance Area
Slide 5
Danger Bearings
Intent:• By monitoring bearing to a landmark
Stay away from danger
SKILL• Plotting and Labeling Danger Bearings• Monitoring the bearing on the water
Slide 6
Constructing a Danger Bearing
Slide 7
Constructing a Danger Bearing
Slide 8
Constructing a Danger Bearing
Slide 9
Constructing a Danger Bearing
Slide 10
Constructing a Danger Bearing
Slide 11
Constructing a Danger Bearing
Slide 12
Constructing a Danger Bearing
Slide 13
Constructing a Danger Bearing
Slide 14
Constructing a Danger Bearing
Slide 15
Constructing a Danger Bearing
Slide 16
Constructing a Danger Bearing
Slide 17
Constructing a Danger Bearing
Slide 18
Monitoring Position
Danger Bearings
• Visual bearings Hand-bearing compass Monitor bearing to landmark
• GPS bearings Enter landmark as waypoint Monitor GPS bearing to landmark
© 2003, R J Sweet, “GPS for Mariners.” Reprinted with permission© 2004 “The Weekend Navigator”
Slide 19
Using Danger Bearings
Slide 20
Danger Sector
Slide 21
Exercise 4-1 – Danger Bearing
Take out Bowditch Bay chart
Plot and label danger bearing
Slide 22
Solution to Exercise 4-1
Slide 23
Crosstrack Error
Feature in GPS
• Data Field Indicates deviation from course line Left or Right of intended course Distance in feet or nautical miles
• Alarm An alarm can be set Sounds if exceed crosstrack error
Slide 24
Crosstrack Error
Uses
• Stay close to course line
• Boat freely within lateral limits Sailing
Slide 25
Crosstrack Error – Avoid Hazards
© 2003, R J Sweet, “GPS for Mariners.” Reprinted with permission© 2004 “The Weekend Navigator”
Slide 26
Determining an Avoidance Region
rhumb line
alarm upon exit
© 2003, R J Sweet, “GPS for Mariners.” Reprinted with permission© 2004 “The Weekend Navigator”
Slide 27
Using Crosstrack Error
Slide 28
Exercise 4-2
Using Bowditch Bay chart
Plot & label – Crosstrack Error
Slide 29
Solution to Exercise 4-2
Slide 30
Danger Circles
Danger circles Similar concept to danger bearing Danger is within or outside of the circle
Measuring a danger circle• GPS
Anchor watch (stay within the circle) Avoidance waypoint (stay outside the circle) Alarmed
• Radar Monitor radius to an object Guard zone
– Alarmed
© 2003, R J Sweet, “GPS for Mariners.” Reprinted with permission© 2004 “The Weekend Navigator”
Slide 31
Avoidance Waypoint
© 2003, R J Sweet, “GPS for Mariners.” Reprinted with permission© 2004 “The Weekend Navigator”
Slide 32
Using Danger Circles
Slide 33
Danger Circles
Slide 34
Exercise 4-3 – Danger Circles
Take out Bowditch Bay chart
Plot and label – danger circle• Use radar VRM
Slide 35
Solution to Exercise 4-3
Slide 36
Putting it all Together
Slide 37
Danger Bearing - 1
Slide 38
Danger Bearing - 2
Slide 39
Danger Bearings Define Entrance
Slide 40
Alternative – GPS Bearing + XTE
Slide 41
Danger Circles
Slide 42
Putting it all Together
Slide 43
Other Avoidance Techniques
GPS
• Mark boundaries Linear boundary (artificial buoys) Cardinal boundary (N-S-E-W of danger)
Digital Chart Navigation
• Computer Create any shape for a danger area Tied to an alarm Can select exit or entrance alarm
– Alarm when leave (e.g., anchor watch)– Alarm when enter (e.g., danger area)
© 2003, R J Sweet, “GPS for Mariners.” Reprinted with permission© 2004 “The Weekend Navigator”
Slide 44
Adding Waypoints to Define Shallows
© 2003, R J Sweet, “GPS for Mariners.” Reprinted with permission© 2004 “The Weekend Navigator”
Slide 45
Alarms on a Chart Screen
© 2003, R J Sweet, “GPS for Mariners.” Reprinted with permission© 2004 “The Weekend Navigator”
Slide 46
Safe Area Alarm
Slide 47
Questions ? … Comments