Transcript United States Power Squadrons ® Advanced Piloting Course Chapter 9 Plotting with Winds & Currents.

United States Power Squadrons
®
Advanced Piloting Course
Chapter 9
Plotting with Winds & Currents
Understanding Vectors
6kn
Boat Speed
Boat Speed Over Ground
Current
2kn
8kn
Slide 2
Against the Current
6kn
Boat Speed
Boat Speed Over Ground
4kn
2kn
Current
Slide 3
Currents in Channels
 Currents are significant in narrow channels
• Restriction enhances speed
 Generally, boats move with or against
current
• Effect on boat’s Speed Over Ground
• Little effect on boat’s direction
Slide 4
Currents in Open Water
 Currents can be crossing
• Currents may act across a large area
 Boats can experience current at any angle
• Causes an effect on direction
• And an effect on speed
 Solve graphically
Slide 5
Cross Current
Boat Course Steered & Speed
6kn
2kn
7kn
Slide 6
Solve Graphically
 Scale diagram
• Use same period of time for all vectors
– Boat Course
– Current
– Boat Track (COG)
 Length of line = distance traveled in that time
– Use: 60D = ST
• Convenient technique
 Use One Hour (length of line = speed)
 Plot two lines, solve for third
Slide 7
Terminology
 Actual Course
• Course over Ground (COG)
• Speed over Ground (SOG)
 DR Course
• Course Steered
• Speed of Boat (through water)
 Current
• Set (direction of flow)
• Drift (speed of current)
Slide 8
Terminology
 Intended Course
• Path you really want to take
• Course over Ground (COG)
 Solve for Course to Steer (DR course)
 Intended Speed
• Desired Speed over Ground
 Solve for Speed of Boat (DR speed)
• Determine net Speed over Ground
 Use Speed of Boat, solve for SOG
Slide 9
Determine Set & Drift
 Compare
• Actual Position
 Fix
– bearings
– GPS
– close aboard – navigation aid
• Expected Position
 Based on Course Steered
 DR position
– distance traveled
 Plot
• Construction line between DR and Fix
• Measure
 Direction (set)
 Distance
• Determine
 Speed (drift) using 60D = ST
Slide 10
Determining Set & Drift
Slide 11
Determining Set & Drift
Slide 12
Determining Set & Drift
Slide 13
Determining Set & Drift
Slide 14
Determining Set & Drift
Slide 15
Determining Set & Drift
Slide 16
Determining Set & Drift
Slide 17
Determining Set & Drift
Slide 18
Exercise 9-1
 Get Out Bowditch Bay chart
 You have a GPS fix
• Plot your DR position
• Draw dashed line between DR and Fix
 Measure
• Set direction
 Calculate
• Drift speed
Slide 19
Solution to Exercise 9-1
Slide 20
Determine Course to Steer
 Need
• Expected Set & Drift
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Direct measurement
Current tables
Local knowledge
Other boaters
 Plot
• Intended Course
 Direction
 Will be Course over Ground when taken (COG)
Slide 21
Two Techniques
 Two techniques
• Based on:
 (1)
–
 (2)
–
The boat Speed is fixed
Speed of Advance (SOG when taken) depends on current
The intended Speed of Advance is fixed (optional)
Then need to know what boat speed needed
• In both cases…
 You will determine the course (DR) to steer
– Different in each case
Slide 22
Plotting Course to Steer (1)
Slide 23
Plotting Course to Steer (1)
Slide 24
Plotting Course to Steer (1)
Slide 25
Plotting Course to Steer (1)
Slide 26
Plotting Course to Steer (1)
Slide 27
Plotting Course to Steer (1)
Slide 28
Plotting Course to Steer (1)
Slide 29
Plotting Course to Steer (1)
Slide 30
Plotting Course to Steer (1)
Slide 31
Plotting Course to Steer (1)
Slide 32
Plotting Course to Steer (1)
go to Method 2
Slide 33
Exercise 9-2
Homework Exercise
 Get out Bowditch Bay Chart
 Plot
• Your intended course
• Set and Drift
 Use a 1 hr plot
• Use compass
 Plot distance traveled at boat speed in 1 hr
 Measure Course direction
 Determine
• Speed of advance (SOG when underway)
Slide 34
Solution to Exercise 9-2
Slide 35
Exercise 9-2
 What’s wrong with this solution?
• The Course to Steer crosses rocks
 While your actual track should be along COG
 Suppose you made a mistake, or
 Suppose the wind or current changed
• More prudent approach
 Select a route to avoid the danger altogether
Slide 36
Slide 37
Course to Steer (optional)
 Most boaters establish the speed
• Operate the boat at an efficient speed in the water
• Use Course to Steer (1)
 Occasionally time of arrival is important
• If the boat has the capacity for more speed
• May choose to determine the needed SOG
• Then graphically determine the boat speed
 That will get you there on time
 Option (2) – not graded
Slide 38
Plotting Course to Steer (2)
Slide 39
Plotting Course to Steer (2)
Slide 40
Plotting Course to Steer (2)
Slide 41
Plotting Course to Steer (2)
Slide 42
Plotting Course to Steer (2)
Slide 43
Plotting Course to Steer (2)
Slide 44
Plotting Course to Steer (2)
Slide 45
Plotting Course to Steer (2)
Slide 46
Staying on Course
 GPS can solve Course to Steer
• Matter of technique
• No graphics or vectors
Slide 47
Pushed Off-Course
© 2004 “The Weekend Navigator”
Slide 48
Correcting Course
© 2004 “The Weekend Navigator”
Slide 49
Staying On-Course
© 2004 “The Weekend Navigator”
Slide 50
Symbol Summary
Slide 53
Plotting & Labeling Summary
Slide 54
Summary
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Electronic Navigation - Primary
All new material
Extensive Hands-On Exercises
Practical Material
Extensive Color graphics
Slide 55
Questions ? … Comments
Slide 56
Homework
Chapter 9 - Solutions
Exercise 9-2
Homework Exercise
 Get out Bowditch Bay Chart
 Plot
• Your intended course
• Set and Drift
 Use a 1 hr plot
• Use compass
 Plot distance traveled at boat speed in 1 hr
 Measure Course direction
 Determine
• Speed of advance (SOG when underway)
Slide 58
Solution to Exercise 9-2
Slide 59
Exercise 9-2
 What’s wrong with this solution?
• The Course to Steer crosses rocks
 While your actual track should be along COG
 Suppose you made a mistake, or
 Suppose the wind or current changed
• More prudent approach
 Select a route to avoid the danger altogether
Slide 60
Slide 61
Exercise 9-3 – Set & Drift in Navigation
 Get out Bowditch Bay chart
• homework problem
 Navigating with Set & Drift
• Determine set & drift
 Using actual and predicted position
• Use set & drift
 In determining the course to steer
Slide 62
Solution Exercise 9-3
Slide 63