1. Boating Skills & Seamanship
Lesson 9
Introduction to Navigation
Approved by DC-E USCG AuxA, Inc

2. Lesson Objectives Select, Use, And Keep Current Charts
Identify Objects On A Chart
Use Piloting Tools
Compass Mounting
Determining Position (LOP)
Measuring Distance On Charts
Principles Of Dead Reckoning
Compute Time,Speed, And Distance

3. Navigator’s Tools Charts Magnetic Compass
Course Plotter – Parallel Rulers
Dividers
Good Pencils - Erasers
Binoculars - 7 x 50
Means Of Finding Water Depth
Electronic Tools

4. Map vs Chart Map Nautical Chart
Symbolic picture of a position of the earth drawn to scale
Nautical Chart
Map that emphasizes features useful to the mariner
Shape of the coastline
Landmarks
Depths

5. Chart Projection
Converts Spherical Area (Earth) To A Flat Piece Of Paper (Chart)
Two Main Types Of Projections
Mercator
Conical

6. The Mercator Projection
Points On The Earth Projected Onto Cylinder
Portions Of Cylinder Become Flat Surface When Cut Apart
All Angles Correctly Represented So Course Lines Can Be Measured Accurately
Distortion Magnified As You Go North Or South, So Unusable Near Poles

7. A A Mercator Projection Lines of Longitude Projected Parallel
The Further Away From The Equator,
The Greater The
Distortion
Spherical Surface Projected On A
Cylinder

8. The Polyconic Projection
Earth’s Surface Projected On A Series Of Cones
Less Distortion At High Northern And Southern Latitudes
Measuring Can Only Be Done From The Center Of The Chart

9. Less Distortion in Northern/Southern Areas
Conical Projection
Less Distortion in Northern/Southern Areas

10. Strip Charts Segments Of Larger Traditional Charts
Printed On Small Panels & Enclosed In A Folder
Easier To Handle On Small Boat
Sections May Not Be Printed With North At The Top

11. General Information Block

12. Chart Scales Large Scale = Small Area Small Scale = Large Area
1:80,000 Smaller Scale Than 1:40,000
1:80,000 Means 1 INCH On CHART Equals 80,000 Inches On Earth
Always Use Largest Scale Possible

13. Chart Scales (Cont) Harbor 1:2,000 1:40,000 Coast 1:40,000 1:150,000
General 1:150,00
1:600,000
Sailing 1:600,000
1:14,000,000

14. Chart Selection
Nautical Chart Catalog 1
Chart Information

15. Chart Datum Datum Vertical Clearance Depth
Benchmark term from which a chart’s vertical or horizontal measurements are made
Vertical Clearance
Based on Mean High Water
Depth
Based on Mean Lower Low Water (MLLW)

16. Boat’s Actual Clearance
Vertical Chart Datum
Actual Clearance
Vertical Clearance
Mean Range
MHW
MLW or MLLW
Height of Tide
Water Depth
Boat’s Actual Clearance
Charted Depth

17. Positions On The Surface Of The Earth
System Of Coordinates
Great Circle - a plane that passes through the center of the earth
When it also passes through both Geographic poles it is a Meridian or Line of Longitude
The Equator is also a Great Circle
Small Circle – any plane passing through the earth but not the CENTER of the earth.
a small circle plane that is parallel to the equator is called a Parallel or Line of Latitude

18. Latitude and Longitude
Parallels of Latitude
Meridians of Longitude

19. Latitude

20. Measuring Latitude Line A-B Line A – C Angle = 60 º
Center of the earth to equator (radius)
Line A – C
Center of earth to parallel
Angle = 60 º A B C

21. Longitude

22. Measuring Direction Use Chart’s Tools Compass Parallel Rulers Dividers
Compass Rose (360° in any direction)
Meridians of Longitude (vertical coordinate)
Parallels of Latitude (horizontal coordinate)
Tools
Compass
Parallel Rulers
Course Plotter
Paraglide Plotter
Dividers

23. The Compass Top Reading Front Reading Inclinometer Direct Digital
Telltale Compass
Fluxgate

24. Compass Errors Variation Deviation
Due to angular difference in direction to true north and magnetic north poles
Same for every boat in one area
Deviation
Due to magnetic influences aboard boat
Different for every boat
Changes with boat heading

25. Understanding Variation
Polar North vs. Magnetic North
Earth’s magnetic core does not coincide with geographical north
Every Chart Will Have 1 to 4 Compass Roses To Indicate Variation Of That Area
An annual increase in variation occurs due to plate tectonics
Increase may be 1’ to 9’ or more each year
Important to use most recent edition of charts

26. Relative Positions of Poles

27. Polar Variation
Variation is the angular difference between the geographic and magnetic meridians
Geographic North Pole
Observer’s position
Magnetic North Pole

28. Compass Points to North Magnetic Pole True North
Area that changes slightly
Far northern Canada
True North
Earth’s axis
Base for latitude and longitude

29. The Compass Rose
As Seen On The Tr Chart South of Rhode Island = True North
= Magnetic North

30. Deviation
Any Magnetic Field Aboard A Vessel Strong Enough To Effect The Compass
Engines, electronic instruments, wires, steering wheel, especially the radio ‘s speaker
Deviation is specific to each individual vessel
Deviation will vary depending upon vessel’s heading
If more than one or two degrees, a DEVIATION TABLE should be constructed

31. Correcting Compass Errors
Tele- T
True Heading V
Variation
Vision M
DOWN
ADD
WEST
Makes
Magnetic Heading D
Dull
Deviation C
Children
Compass Heading
(Add Wonder)

32. True Heading
Compass Rose

33. 015 Degrees West Variation

34. 005 Degrees West Deviation

35. 005 Degrees West Deviation

36. Compass Review Variation Deviation
Local difference, East or West, between the direction of true and magnetic north
Deviation
Error caused by magnetic influences within the boat based on its heading

37. Measuring Distance One Degree Of Latitude Equals 60 Nautical Miles
One Minute Of Latitude Equals One Nautical Mile
Use
Latitude scale at vertical side of chart, or
Distance scale

38. Expressing Course Or Direction
True Heading
Can be affected by variation
Used to plot a course
Magnetic Heading
Difference from true caused by variation
Compass Heading
Deviation from magnetic heading caused by magnetic influences on boat
Used to steer a course

39. Finding Your Position Line of position (LOP) Circle of position (COP)
Range LOP
Bearing LOP
Loran time differential (TD) LOP
Circle of position (COP)
Distance from an object
RADAR
GPS

40. Positioning To Fix Your Position
Where Two Lines Of Position (LOP) Cross
Where Two Circles Of Position (COP) cross
Where one LOP & one distance or COP cross
Third value to validate

41. Positioning Obtaining an LOP Use hand-held compass (bearing)
Turn vessel so bow is centered on object
Range: two objects that line up
LORAN reading
RADAR or GPS reading

42. Fixes
1400 FIX
Where Two LOPs Cross
1400
260
1400
200
Tank
Tower

43. Measuring Speed Speedometers – Give Speed Over Water
On small boats, not especially accurate
More Accurate Speed Indication Based on Tachometer Readings (RPMs)
Still Speed over the Water
Need Speed Over the Bottom (Ground)
Takes into consideration the effects of current and wind
Essential when computing time, speed, and distance problems
Obtain from fixes or electronic (RADAR, GPS or LORAN)

44. Speed Table Determining Speed Direction 1 Direction 2 Average Speed
4 kts
5 kts
7.5 kts
8 kts
RPM
800
1000
1500
2000
3000
Time
12 m
10 m
7 m
6 m
5 m
6 kts
8.5 kts
10 kts
12 kts
15 m
8 m
7.5 m
4.5 kts
6.5 kts
9 kts
11 kts

45. Speed Curve Vessel Run Over Measured Mile RPM SPEED (Kts) 800 1000
800
1000
1500
2000
3000 2 4 6 8 10 12
RPM

46. Computing Distance Speed and Time
Some Examples:
Suppose you drive your boat at a speed of 20 Knots for 12 minutes. How far have you gone?
How long does it take to travel 4 Nautical Miles at a speed of 20 Knots?
How fast are you going if you travel 4 Nautical Miles in 12 minutes?

47. Speed – Distance - Time 60 x D S T “Sixty D Street” 60D=ST S=60 T T=60

48. Computing Formulas Time: T = 60 D /S Distance: D = (S X T) / 60
60 X 4 Miles = 240 / 20 knots = 12 minutes
Distance: D = (S X T) / 60
20 Knots X 12 min = 240 / 60 = 4 Nautical Miles
Speed: S = 60 D / T
60 X 4 Miles = 240 / 12 min = 20 Knots

49. Primary Methods Of Navigation
Dead Reckoning
Piloting
Celestial Navigation
Electronic Navigation
Inertial Guidance

50. Dead Reckoning Deduced Reckoning
Process of determining a ship’s approximate position by applying to the last well determined position, a series of vectors, representing the run that has since been made
Only TRUE courses are used by the Navy and Coast Guard
Small boats can substitute magnetic

51. Dead Reckoning (Cont) Course Fix
From a known position, line along which a vessel is steered.
Written as C & three digit number over line and Speed indicated under line by S & two digits
Fix
An accurate position usually obtained by crossing 2 or more LOPs. Indicated as circle around dot and a time notation
0930 Fix

52. Dead Reckoning (Cont) DR Position EP – Estimated Position
Obtained by vessel’s course and speed from the last accurate position
0930 DR
EP – Estimated Position
Most probable position, determined from bearings of questionable accuracy
0930 EP

53. Dead Reckoning Rules A DR Shall Be Plotted -
Every ½ Hour, on the hour and half hour
At the time of every course change
At the time of every speed change
At the time of obtaining a FIX
At the time obtaining a single LOP

54. Plotting Conventions Course Line LOP DR Position Fix C 090 S 10 1445
1000
1200

55. Typical DR Plot
0900
C120
S10
0930
C150
1010
C055
1055
C020

56. Electronic Navigation
LORAN
Long Range Navigation
GPS
Global Positioning System
Radar
Depth Sounders

57. Waypoints Fixes Where you have been Where you want to go
Used by LORAN and GPS
Entered on the chart
Entered in the receivers
Verify all tracks on a chart for hazards

58. LORAN Radio Signals AM signals Land based antennas Shipboard receivers
Chains - masters and slaves
Shipboard receivers
AM signals
Degradation in bad weather
Some distortion
Some “holes” in coverage

59. GPS The Choice Of Most Recreational Boaters 24 Orbiting Satellites
Readily available
Handheld – Mounted – Plotters
$100+
24 Orbiting Satellites

60. GPS Accuracy SA – Selective Availability DGPS – Differential GPS
Not in use since May 1, 2000
15 meters or 49.2 feet 95%
DGPS – Differential GPS
Land-based supplement
5 meters or 16.4 feet
WASS – Wide Area Augmentation System
2.5 meters or 8.2 feet
Latest GPS incorporates LORAN as well

61. Tides Tides per day Monthly Diurnal Semi-diurnal Mixed Spring Tides
Neap Tides

62. Rule of Twelve One-Two-Three Rule of Thumb Assume a 12 foot tide
Tide may rise or fall
1/12 1st & 6th Hours
2/12 2nd & 5th Hours
3/12 3rd & 4th Hours
Assume a 12 foot tide
1st hour = 1 foot
2nd hour = 3 feet (1+2)
3rd hour = 6 feet (1+2+3)
4th hour = 9 feet ( )
5th hour = 11 feet ( )

63. Three Key Words
PRACTICE

64. Summary (1) Projections Vertical Datum: MHW and MLLW Piloting Tools
Latitude - Longitude
Maps Vs Charts

65. Summary (2) Measuring Distance Variation - Deviation
Lines Of Position - Fixes
Speed - Time - Distance: 60 D ST
Dead Reckoning