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

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

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

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

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

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

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

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

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

General Information Block

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

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

Chart Selection Nautical Chart Catalog 1 Chart Information

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)

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

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

Latitude and Longitude Parallels of Latitude Meridians of Longitude

Latitude

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

Longitude

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

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

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

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

Relative Positions of Poles

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

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

The Compass Rose As Seen On The 1210-Tr Chart South of Rhode Island = True North = Magnetic North

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

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)

True Heading Compass Rose

015 Degrees West Variation

005 Degrees West Deviation

005 Degrees West Deviation

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

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

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

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

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

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

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

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)

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

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

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?

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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 (1+2+3+3) 5th hour = 11 feet (1+2+3+3+2)

Three Key Words PRACTICE

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

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