Transcript Chapt 9 - UUSCGAUX D11NR

Boating Skills &
Seamanship
Lesson 9
Introduction to Navigation
Approved by DC-E USCG AuxA, Inc
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
2
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
3
Map vs Chart
• Map
– 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
4
Chart Projection
• Converts Spherical Area (Earth) To A
Flat Piece Of Paper (Chart)
• Two Main Types Of Projections
– Mercator
– Conical
5
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
6
A Mercator Projection
Lines of Longitude
Projected Parallel
The Further Away
From The Equator,
The Greater The
Distortion
Spherical Surface
Projected On A
Cylinder
A
7
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
8
Conical Projection
Less Distortion in Northern/Southern Areas
9
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
10
General Information
Block
11
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
12
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
13
Chart Selection
• Nautical Chart Catalog 1
• Chart Information
14
Chart Datum
• Datum
– 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)
15
Vertical Chart Datum
Vertical
Clearance
Actual
Clearance
MHW
Mean
Range
MLW or
MLLW
Charted Depth
Boat’s
Actual
Clearance
Height
of Tide
Water
Depth
16
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
17
Latitude and Longitude
Parallels of Latitude
Meridians of Longitude
18
Latitude
19
Measuring Latitude
• Line A-B
– Center of the earth
to equator (radius)
• Line A – C
– Center of earth to
parallel
• Angle = 60 º
C
A
B
20
Longitude
21
Measuring Direction
• Use Chart’s
– 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
22
The Compass
•
•
•
•
•
•
Top Reading
Front Reading
Inclinometer
Direct Digital
Telltale Compass
Fluxgate
23
Compass Errors
• Variation
– 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
24
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
25
Relative Positions
of Poles
26
Polar Variation
• Variation is the angular difference between
the geographic and magnetic meridians
Geographic
North Pole
Magnetic
North Pole
Observer’s
position
27
Compass
• Points to North Magnetic Pole
– Area that changes slightly
– Far northern Canada
• True North
– Earth’s axis
– Base for latitude and longitude
28
The Compass Rose
As Seen On The
1210-Tr Chart
South of Rhode Island
= True North
= Magnetic North
29
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
30
Correcting Compass
Errors
Tele-
T
True Heading
Vision
V
Variation
Makes
M
Magnetic Heading
Dull
D
Deviation
Children
C
Compass Heading
DOWN
ADD
WEST
(Add Wonder)
31
True Heading
Compass
Rose
32
015 Degrees West
Variation
33
005 Degrees
West Deviation
34
005 Degrees
West Deviation
35
Compass Review
• Variation
– 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
36
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
37
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
38
Finding Your Position
• Line of position (LOP)
– Range LOP
– Bearing LOP
– Loran time differential (TD) LOP
• Circle of position (COP)
– Distance from an object
– RADAR
– GPS
39
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
40
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
41
Fixes
Where Two LOPs Cross
Tank
Tower
42
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)
43
Speed Table
Determining Speed
Direction 1
RPM
800
1000
1500
2000
3000
Time
12 m
10 m
7m
6m
5m
Speed
5 kts
6 kts
8.5 kts
10 kts
12 kts
Direction 2
Time
15 m
12 m
8m
7.5 m
6m
Speed
4 kts
5 kts
7.5 kts
8 kts
10 kts
Average
Speed
4.5 kts
6.5 kts
8 kts
9 kts
11 kts
44
Speed Curve
Vessel Run Over Measured Mile
12
SPEED (Kts)
10
8
6
4
2
0
RPM
0
800
1000
1500
2000
3000
45
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?
46
Speed – Distance - Time
“Sixty D Street”
60D=ST
S=60
T
T=60
S
D=ST
60
60 x D
S
T
47
Computing Formulas
• Time: T = 60 D /S
– 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
48
Primary Methods Of
Navigation
•
•
•
•
•
Dead Reckoning
Piloting
Celestial Navigation
Electronic Navigation
Inertial Guidance
49
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
50
Dead Reckoning (Cont)
• Course
– 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
51
Dead Reckoning (Cont)
• DR 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
52
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
53
Plotting Conventions
• Course Line
C 090
S 10
• LOP
1445
090
• DR Position
• Fix
1200
54
Typical DR Plot
0900
55
Electronic Navigation
• LORAN
– Long Range Navigation
• GPS
– Global Positioning System
• Radar
• Depth Sounders
56
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
57
LORAN
• Radio Signals
– Land based antennas
• Chains - masters and slaves
– Shipboard receivers
• AM signals
– Degradation in bad weather
– Some distortion
– Some “holes” in coverage
58
GPS
• The Choice Of Most Recreational Boaters
– Readily available
– Handheld – Mounted – Plotters
– $100+
• 24 Orbiting Satellites
59
GPS Accuracy
• SA – Selective Availability
– 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
60
Tides
• Tides per day
– Diurnal
– Semi-diurnal
– Mixed
• Monthly
– Spring Tides
– Neap Tides
61
•
Rule of Twelve
One-Two-Three Rule of Thumb
• Tide may rise or fall
1. 1/12 1st & 6th Hours
2. 2/12 2nd & 5th Hours
3. 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 (1+2+3+3)
5th hour = 11 feet (1+2+3+3+2)
62
Three Key Words
PRACTICE
PRACTICE
PRACTICE
63
Summary (1)
•
•
•
•
•
Projections
Vertical Datum: MHW and MLLW
Piloting Tools
Latitude - Longitude
Maps Vs Charts
64
Summary (2)
•
•
•
•
•
Measuring Distance
Variation - Deviation
Lines Of Position - Fixes
Speed - Time - Distance: 60 D ST
Dead Reckoning
65