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Boating Skills & Boating Skills & SeamanshipSeamanship

Boating Skills & Boating Skills & SeamanshipSeamanship

Lesson 9Introduction to

Navigation

2

• 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

Lesson ObjectivesLesson Objectives

3

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

Navigator’s ToolsNavigator’s Tools

4

• 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

Map vs ChartMap vs Chart

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• Converts Spherical Area (Earth) To A Flat Piece Of Paper (Chart)

• Two Main Types Of Projections– Mercator– Conical

Chart ProjectionChart Projection

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• 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

The Mercator ProjectionThe Mercator Projection

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The Further AwayThe Further AwayFrom The Equator,From The Equator,The Greater TheThe Greater TheDistortionDistortion

Lines of Longitude Lines of Longitude Projected ParallelProjected Parallel

Spherical Surface Spherical Surface Projected On AProjected On ACylinderCylinder

AA

A Mercator ProjectionA Mercator Projection

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• 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

The Polyconic ProjectionThe Polyconic Projection

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Less Distortion in Northern/Southern Areas

Conical ProjectionConical Projection

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• 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

Strip ChartsStrip Charts

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General Information BlockGeneral Information Block

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• 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

Chart ScalesChart Scales

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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

Chart Scales (Cont)Chart Scales (Cont)

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• Nautical Chart Catalog 1

• Chart Information

Chart SelectionChart Selection

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• 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)

Chart DatumChart Datum

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Vertical Chart DatumVertical Chart Datum

Boat’s Actual

Clearance

Mean Range

MHW

MLW orMLLW

Actual Clearance

Vertical Clearance

WaterDepth

Height of Tide

Charted Depth

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• 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

Positions On The Surface Of The Earth

Positions On The Surface Of The Earth

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Parallels of Latitude

Meridians of Longitude

Latitude and LongitudeLatitude and Longitude

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LatitudeLatitude

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Measuring LatitudeMeasuring Latitude

• Line A-B– Center of the earth

to equator (radius)

• Line A – C

– Center of earth to parallel

• Angle = 60 ºA

B

C

21

LongitudeLongitude

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• 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

Measuring DirectionMeasuring Direction

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The CompassThe Compass

• Top Reading• Front Reading• Inclinometer• Direct Digital• Telltale Compass• Fluxgate

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• 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

Compass ErrorsCompass Errors

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• 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

Understanding VariationUnderstanding Variation

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Relative Positions of Poles

Relative Positions of Poles

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Polar VariationPolar Variation

• Variation is the angular difference between the geographic and magnetic meridians

Observer’s position

Geographic North Pole

Magnetic North Pole

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• Points to North Magnetic Pole– Area that changes slightly– Far northern Canada

• True North– Earth’s axis– Base for latitude and longitude

CompassCompass

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As Seen On The 1210-Tr ChartSouth of Rhode Island

= True North

= Magnetic North

The Compass RoseThe Compass Rose

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DeviationDeviation

• 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

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TT

VV

MM

DD

CC

Tele-Tele-

VisionVision

MakesMakes

DullDull

ChildrenChildren

True HeadingTrue Heading

VariationVariation

Magnetic HeadingMagnetic Heading

DeviationDeviation

Compass HeadingCompass Heading

DOWNDOWNADDADD

WESTWEST

(Add Wonder)(Add Wonder)

Correcting Compass ErrorsCorrecting Compass Errors

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True HeadingTrue Heading

Compass Rose

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015 Degrees West Variation

015 Degrees West Variation

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005 Degrees West Deviation005 Degrees

West Deviation

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005 Degrees West Deviation005 Degrees

West Deviation

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Compass ReviewCompass 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

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• 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

Measuring DistanceMeasuring Distance

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• 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

Expressing Course Or Direction

Expressing Course Or Direction

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Finding Your PositionFinding 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

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• 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

PositioningPositioning

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PositioningPositioning

• 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

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Tower

Tank

1400

260

1400

200

1400

FI

XWhere Two LOPs Cross

FixesFixes

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• 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)

Measuring SpeedMeasuring Speed

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Speed TableSpeed 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

Speed

5 kts

6 kts

8.5 kts

10 kts

12 kts

Time

15 m

12 m

8 m

7.5 m

6 m 10 kts

Speed

4.5 kts

6.5 kts

8 kts

9 kts

11 kts

45RPM

SP

EE

D (

Kts

)

Vessel Run Over Measured Mile

0 800 1000 1500 2000 30000

2

4

6

8

10

12

Speed CurveSpeed Curve

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• 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?

Computing Distance Speed and Time

Computing Distance Speed and Time

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“Sixty D Street” 60D=ST

S=60T

T=60S

D=ST60

60 x D60 x D

SS TT

Speed – Distance - TimeSpeed – Distance - Time

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• 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

Computing FormulasComputing Formulas

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• Dead Reckoning

• Piloting

• Celestial Navigation

• Electronic Navigation

• Inertial Guidance

Primary Methods Of Navigation

Primary Methods Of Navigation

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• 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

Dead ReckoningDead Reckoning

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• 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

Dead Reckoning (Cont)Dead Reckoning (Cont)

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• 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

Dead Reckoning (Cont)Dead Reckoning (Cont)

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• 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

Dead Reckoning RulesDead Reckoning Rules

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• Course Line

• LOP

• DR Position

• Fix 1200

C 090

S 101445

090

1000

Plotting ConventionsPlotting Conventions

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0900

C120S10 0930

C150S10

1010

C055

S10

1055

C02

0S

10

Typical DR PlotTypical DR Plot

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• LORAN– Long Range Navigation

• GPS– Global Positioning System

• Radar

• Depth Sounders

Electronic NavigationElectronic Navigation

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WaypointsWaypoints

• 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

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• Radio Signals– Land based antennas

• Chains - masters and slaves

– Shipboard receivers

• AM signals– Degradation in bad weather– Some distortion– Some “holes” in coverage

LORANLORAN

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GPSGPS

• The Choice Of Most Recreational Boaters– Readily available – Handheld – Mounted – Plotters– $100+

• 24 Orbiting Satellites

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• 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

GPS AccuracyGPS Accuracy

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TidesTides

• Tides per day– Diurnal– Semi-diurnal– Mixed

• Monthly– Spring Tides– Neap Tides

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• One-Two-Three Rule of Thumb• Tide may rise or fall

1. 1/12 1st & 6th Hours2. 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)

Rule of TwelveRule of Twelve

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PRACTICE

PRACTICE

PRACTICE

Three Key WordsThree Key Words

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Summary (1)Summary (1)

• Projections

• Vertical Datum: MHW and MLLW

• Piloting Tools

• Latitude - Longitude

• Maps Vs Charts

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Summary (2)Summary (2)

• Measuring Distance

• Variation - Deviation

• Lines Of Position - Fixes

• Speed - Time - Distance: 60 D ST

• Dead Reckoning