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Piloting Course Chapter 3
Plotting & Planning Techniques
United States Power Squadrons ®
Slide 2
Basic Plotting Techniques
Dead Reckoning• Determining position from prior fix
Bearings• Visually establish a position
2 Bearings establish a fix
• Related techniques Ranges Relative Bearings Seaman’s Eye
Slide 3
SKILL – Dead Reckoning
Maintain Position using
• Course &
• Distance Traveled
SKILL• Plot and Label DR Courses
Slide 4
Dead Reckoning
POSITION determined by:• Course Steered• Distance Traveled
DISTANCE determined by:• Direct-reading LOG• Speed x Time
60 Distance (nm) = Speed (knots) x Time (min)
or 60D = ST (called ‘60 D Street’)
© 2003, R J Sweet, “GPS for Mariners.” Reprinted with permission© 2004, “The Weekend Navigator”
Slide 5
Dead Reckoning
Slide 6
Dead Reckoning Formula
Distance = S x T
(distance traveled)
(average actual speed)
(elapsed time)
60
T
S
Speed = 60 x D
Time = 60 x D
Slide 7
DR Accuracy
Helmsman Issues:• Accuracy of Course Steered
Cannot wander
• Accuracy of Speed Reading Difficult to obtain precise value
• Measurement of Time
Other factors:• Currents & Winds• Obstacles and other boats• Fatigue
Slide 8
DR Plotting & Labeling
DR Plot• Direction of Course Steered
DR Position• Nominally every hour
Calculate and Plot Distance traveled
• Plot at every Course or Speed Change
• Label Dot for location, surrounded by half-circle Time labeled on diagonal
Slide 9
Labeling DR Courses
C 070 M
S 6.01000
2. Label COURSE near starting point “C” (direction – 3 digits)
3. Label SPEED near starting point “S” (kn – 2 significant digits)
1. Draw & Measure COURSE LINE using course direction
4. Plot & Label DR Position dot – half circle Time (4 digits on diagonal)
1030
D = (S x T) / 60
D = (6.0 x 30) / 60
D = 3.0 nmFix
Slide 10
Exercise 3-1 – Plot & Label DR
Use Bowditch Bay Chart
Follow Instructions in Student Guide
Slide 11
Exercise 3-1How to maintain a DR plot. Using “Seaman’s Eye” to confirm DR positions.
At 0945, depart G “1” Fl G 2s Oyster River on a true course of 075º. Speed is 6.5kn.
At 1010, you change to a magnetic course of 355º.
At 1030, you increase speed to 8.5kn.
At 1105, you take up a true course of 090º.
What is a visual check on the 1030 DR position?
What is your sounding at the 1105DR position?
0945
T = 075V = 015WM = 090
C 090M
S 6.5
D = (ST)/60D = (6.5x25)/60D = 2.7nm
M = 355V = 015WT = 340 C
355M
S 6.5
1010
D = (ST)/60D = (6.5x20)/60D = 2.2nm
1030
C 355M
S 8.5
D = (ST)/60D = (8.5x35)/60D = 5.0nm
T = 090V = 015WM = 105
1105C 105M
S 8.5
Slide 12
SKILL – Bearings
Determine Position using
• Visual Bearings to Charted Objects
SKILL• Plot and Label Bearings
Slide 13
Bearings
Lines of Position (LOP)
• Based on direction of visible charted Landmarks
Direction from boat to landmark Plotted toward landmark Your location is somewhere on that line
– You cannot tell precisely where– You can estimate your position at the intersection
» DR Plot and LOP
• Taken on the Water Plotted & Labeled in real time Labeled
– Time of LOP on top of line– Bearing (Magnetic) below line
Slide 14
Sight Bearing from Boat to Landmark
Slide 15
Plot & Label Bearing
1030
070 M
Label Time abovethe line, andBearing belowthe line,
Slide 16
Methods – Taking Bearings
Hand-Bearing Compass
• Every boat should have one Handy Reasonably accurate Easy to use Good as backup compass
• Sight across ship’s compass Limited Inaccurate
© 2003, R J Sweet, “GPS for Mariners.” Reprinted with permission© 2004, “The Weekend Navigator”
Slide 17
Using Landmarks
Slide 18
Exercise 3-2 - Plot & Label Bearings
Use Bowditch Bay
Follow instructions in Student Guide
Slide 19
Exercise 3-2
Method for taking and plotting compass bearings. Plot and label the magnetic course, bearings & DR positions.
At 1005, depart R “8” I Q R Main Channel on a true course of 080º. Speed is 6.2kn.
At 1035, using a hand bearing compass, you take a bearing of 185º on R “6” Fl R4s Main Channel. Using “Seaman’s Eye”, how can you verify this bearing?
At 1110, you take a compass bearing of 355º on the Duttons Island light. What does this tell you about your speed?
1005C 095M
S 6.2
1035
T = 080V = 015WM = 095
D = (ST)/60D = (6.2x30)/60D = 3.1nm
MB = 185V = 015WTB = 170
1035
185M
D = (ST)/60D = (6.2x35)/60D = 3.6nm
MB = 355V = 015WTB = 340
1110
355M
1110
Slide 20
SKILL – 2-Bearing FIXes
Develop a FIX using
• Two Bearings
SKILL• Plot and Label Fixes
Slide 21
Fixes – 2 Bearings
FIX• Intersection of 2 or more Bearings
Accuracy• Determined by accuracy of each bearing• Depends on angle between bearing
Too close, poor accuracy (< 30°) (> 150°) 90° = ideal (2 bearings)
Slide 23
2-Bearing FIX
1030
070 M
1030
340 M
Slide 24
Exercise 3-3 - 2 Bearing FIX
Use Bowditch Bay chart
Follow Instructions in Student Guide
Slide 25
Using two bearings to plot a fix.
At 0900, depart RW “OR” Mo (A) Oyster River on a true course of 350º. Speed is 6.0kn.
At 0936, you take a compass bearing of 285º on Chapman Point light and a compass bearing of 355º on the light house north of Shark River. At the 0936 fix, take up a magnetic course of 077º. Increase speed to 11kn.
What are the L and Lo of the 0936 fix?
Observe the 0936 DR and fix positions. What happended?
Using “Seaman’s Eye”, what can you say about your 0936 fix?
Exercise 3-3
0900
C 005M
S 6.0T = 350
V = 015WM = 005
0936 285M
0936
355M
D = (ST)/60D = 6.0x36/60D = 3.6nm
CB = 285V = 015WTB = 270
CB = 355V = 015WTB = 340
09360936
M = 077V = 015WT = 062
C 077M
S 11
41º 41.4’N
72º 01.3’W
Slide 26
SKILL – 3-Bearing FIXes
Develop a FIX using
• Three or more Bearings
SKILL• Plot and Label 3-Bearing Fixes
Slide 27
3-Bearing FIX
3 Bearings • May not line-up• Potential for 3 intersections
Forms a triangle Position nominally at center of triangle
Slide 28
BREAK FOR THIS CHAPTER
Slide 29
Relative Bearings
Bearings using the Boat as reference
• Used occasionally
• Need obvious reference points on boat Bow Bearings Beam Bearings
• Falls into category of “Seaman’s Eye” Not precise, but good check
Slide 31
SKILL – Relative Bearings
Take Bearings relative to the Boat• Bow Bearing• Beam Bearing
SKILL• Plot and Label Relative Bearings
Slide 32
Bow Bearing
1030
070 M
070 M
Slide 33
Beam Bearing
1030
160 M
070 M
90R
Slide 34
Beam Bearing
1030
340 M
070 M
270 R
Slide 35
Exercise 3-4 - Relative Bearings
Use Bowditch Bay chart
Follow instructions in Student Guide
Slide 36
Using “Seaman’s Eye” to take bow and beam relative bearings.
At 1000, depart RW “OR’ Mo (A) on a true course of 349º. Speed is 6.0kn.
At 1019, you take a starboard beam bearing by “Seaman’s Eye” on R “10” Q R Main Channel.
At 1100, you briefly turn the bow toward Fl R 6s 40ft 10M HORN north of Shark River and take a bow bearing of 344ºM, and notice that the light on Chapman’s Point is exactly off your port beam. Plot the 1100 fix and steer a new course of 105ºM.
At 1147, you take a port beam bearing on the tower with a red light to the north.
Exercise 3-4
1000
C 004M
S 6.0
T = 349V = 015WM = 004
1019
094M
1100
344M
D = (ST)/60D = 6.0x19/60D = 1.9nm
RB = 090MH = 004MB = 094V = 015WTB = 079
1019
1100
D= (ST)/60D=(6.0x41)/60D= 4.1nm
1100
254M
RB = 000MH = 344MB = 344V = 015WTB = 329
1100
RB = 270MH = 344MB = 254V = 015WTB = 239
M = 105V = 015WT = 090
C 105M S 6.0
D = (ST) / 60D=(6.0x47)/60D = 4.7nm
1147
RB = 270MH = 105MB = 375V = 015WTB = 360
1147 015M
Slide 37
SKILL – Ranges
Pre-plotted Bearings using• Two visible charted landmarks or• Navigation aids
Provides a visual cue on the water to• Stay on Course• Find a specific location
SKILL• Use Ranges, Plot and Label your own
Ranges
Slide 38
Ranges
Ranges are Pre-Plotted Bearings• Use two visible charted landmarks• Bearing line intersects both
landmarks
Uses• Navigation in narrow channels• Alignment with Harbors• Formal navigation aids• Can build own to help navigate
Very Precise
© 2003, R J Sweet, “GPS for Mariners.” Reprinted with permission© 2004, “The Weekend Navigator”
Slide 39
Using a Range
© 2003, R J Sweet, “GPS for Mariners.” Reprinted with permission© 2004, “The Weekend Navigator”
Slide 40
Formal Range
© 2003, R J Sweet, “GPS for Mariners.” Reprinted with permission© 2004, “The Weekend Navigator”
Slide 41
Informal Range
Slide 42
Range Pictures
Slide 43
Exercise 3-5 - Ranges
Use Bowditch Bay chart
Follow instructions in Student Guide
Slide 44
Select and measure ranges from any two charted landmarks.
Create a range to the entrance of Perkins Cove, approaching it from the North on a magnetic course of approximately 200º. Assume that the tower on the west side of Perkins Cove is illuminated and its height to be 40ft.
Plot the range and create a turn into Perkins Cove
Exercise 3-5 – Ranges
T = 185V = 015WM = 200
Ran
ge
200M
T = 156V = 015WM = 171
C 171M
Slide 45
Seaman’s Eye
Informal Ranges
Bow & Beam Bearings
Other Reference Points on the Boat• Mark on rail
Slide 46
Using GPS to Navigate
Using GPS
• You get Precise Position – continuously
• But, how do you navigate and stay safe?
• Must periodically plot position on a chart
Essential to have reference to what is nearby Or, along your path Can be a tedious task
Slide 47
Better Approach: Pre-Planning
Create pre-qualified legs on the water
• Qualify them to be free of obstacles
Then, On-the-water – follow the paths
• Only need to refer to charts on occasion• Key – just stay on course
Slide 48
Pre-Planning
1. Make your plan
2. Follow your Plan
Slide 49
Characteristics of a Safe Path
1. Clear of Obstacles
2. Sufficient Depth for boat
Slide 50
Selecting a Safe Path
Step-by-Step
1)Draw ‘legs’ (paths)
2)Check for obstacles Shallow Water Rocks Wrecks Other Obstacles (poles, structures, etc.)
3)Safe Path Width Nominally about 1/10th nm on each side
– Equal to smallest increment on latitude scale– About 600 feet
Allows for helmsmanship, other boats, some drift
© 2003, R J Sweet, “GPS for Mariners.” Reprinted with permission© 2004, “The Weekend Navigator”
Slide 51
Minimum Path Width
Slide 52
Hazard Symbols
Redrawn from “How to Read a Nautical Chart”
Slide 53
Symbols for Obstructions
From: “How to Read a Nautical Chart”
Slide 54
What to look for…
Use Navigation Aids• Try to begin / end legs at navigation
aids Gives visible reference
Use visible landmarks• Provides a double-check reference
Take bearings as you go along
Depth• Sufficient clearance under the keel
© 2003, R J Sweet, “GPS for Mariners.” Reprinted with permission© 2004, “The Weekend Navigator”
Slide 55
Depth under the Boat
Slide 56
Working Around Obstacles
Build a Route Around Obstacles
• Create multiple legs
© 2003, R J Sweet, “GPS for Mariners.” Reprinted with permission© 2004, “The Weekend Navigator”
Slide 57
Planning on a Chart
© 2003, R J Sweet, “GPS for Mariners.” Reprinted with permission© 2004, “The Weekend Navigator”
Slide 58
Waypoint Terminology
Slide 61
Digital Charting - CD
Slide 63
Autoplay Menu
Slide 64
Simple Tools
Slide 65
A to B Measurements
Slide 66
Marking on Chart
Slide 67
Quick Route
Slide 68
Questions ? … Comments