session 1 nautical charts

Session 1Session 1Nautical Nautical ChartsCharts

Even though you have taken a navigation course before……you will probably learn some new tricks today that will make your boating a little easier and safer.

ObjectivesObjectives To become familiar with data found on

Nautical Chart and how it relates to GPS and the (P)ATON Program.

To understand chart orientation. To be introduced to the compass rose

and understand variation error. To become familiar with the data found

in the General Information Block on a nautical chart.

To understand how depths are

depicted on a nautical chart.

To become familiar with the symbols and abbreviations found on a nautical chart.

To understand the scale of a nautical chart.

To be introduced to the horizontal and vertical datum on a nautical chart and their effect on GPS sets and accuracy.

To be introduced to the symbols that represent Aids to Navigation on a nautical chart.

To learn to read bottom characteristics on a nautical chart.

To help you understand the critical relationships between your GPS set and a nautical chart.

Why you need to use a Why you need to use a Nautical Chart with GPS.Nautical Chart with GPS.

The Nautical Chart is the road map for the sea.

“An accident at sea… …can ruin a good day.”

Knowing how to read a Knowing how to read a nautical chart helps you:nautical chart helps you:

Identify any hazards and dangers along your course line.

Effectively plot a course on your chart.

GPS NoteGPS Note:: A nautical chart provides a clearer understanding of the geography of the area where your GPS system is operating.

Another GPS Note:While underway, a paper

nautical chart is much easier and safer to use

than a GPS chart plotter.

The Mercator Projection.The Mercator Projection. Converts the earth’s sphere onto a flat

surface usable as a chart.

Projects the earth’s sphere onto a cylinder.

True North is usually at the top of the Mercator projection.

The distance between Meridians of Longitude becomes distorted as you move away from the equator toward the Poles.

The The Mercator Mercator

ProjectionProjection

Mercator Conformal

The Earth as a Sphere.The Earth as a Sphere. True Geographical North is found at the

top of the chart. This is the axis on which the earth spins.

Circumference of the earth is 21,614 nautical miles. [ Divide by 360 degrees to get 60 nm per degree.]

Magnetic North is 016 degrees West of Geographical north in the Boston area.

The Equator

The Prime Meridian

THE EARTH

as aGLOBE

The North PoleThe

Magnetic North Pole

The angular difference from your position on the earth to

the North and Magnetic North poles is called:

“VARIATION ERROR”

GPS Note: Check that your GPS adjusts for VARIATION automatically!

If not, you must set the VARIATION in your GPS.

Review your “GPS Operation Manual” for the procedure for your GPS set.

MAGNETICMAGNETIC NORTH POLENORTH POLE

WESTERLY WESTERLY VARIATIONVARIATION

WESTERLY WESTERLY VARIATIONVARIATION

EASTERLY EASTERLY VARIATIONVARIATION

GEOGRAPHIC GEOGRAPHIC NORTH POLENORTH POLE

EASTERLY EASTERLY VARIATIONVARIATIONEASTERLY

ANDWESTERLYVARIATION

ANGULAR ANGULAR DIFFERENCE DIFFERENCE

BETWEEN BETWEEN TRUE NORTH TRUE NORTH

AND AND MAGNETIC NORTHMAGNETIC NORTH

EASTERLYEASTERLYVARIATIONVARIATION

0 variation0 variation

21 E variation21 E variation 10 W variation10 W variation

Isogonic LinesIsogonic Lines

1010oo E variation E variation

The North Magnetic Pole moves around.

The Magnetic Pole’s movement throughout

the years

NORTHERNHEMISPHERESOUTHERN

HEMISPHERE

EASTERNHEMISPHERE

WESTERN HEMISPHERE

TTHHEE

GGLLOOBBEE

Parallels Parallels of Latitudeof Latitude

MeridiansMeridians of Longitudeof Longitude

Form Small Circles

Form Great Circles

3030

4545

6060

EQUATOREQUATOR 00

LATITUDE IS MEASUREDLATITUDE IS MEASUREDIN DEGREESIN DEGREES

30 DEGREES NORTH30 DEGREES NORTHLATITUDELATITUDE

30 DEGREES SOUTH 30 DEGREES SOUTH LATITUDELATITUDE

NORTHERNNORTHERNHEMISPHERE ISHEMISPHERE ISNORTH OF THENORTH OF THEEQUATOREQUATOR

SOUTHERNSOUTHERNHEMISPHERE ISHEMISPHERE ISSOUTH OF THESOUTH OF THEEQUATOREQUATOR

SOUTH POLESOUTH POLE

NORTH POLENORTH POLE

LATITUDE LINES ARE PARALLEL AND RUNLATITUDE LINES ARE PARALLEL AND RUNIN TRUE EAST AND TRUE WEST DIRECTIONSIN TRUE EAST AND TRUE WEST DIRECTIONS

3030

15 DEGREES SOUTH 15 DEGREES SOUTH LATITUDELATITUDE

1515

1515

15 DEGREES NORTH 15 DEGREES NORTH LATITUDELATITUDE

7575

45456060

7575

9090

9090

LATITUDELATITUDE

ANIMATIONANIMATION

New England is located:WEST of the Prime Meridian, andNORTH of the Equator.

One Minute

of

Latitude

equals

One Nautical Mile

LONGITUDELONGITUDE

LONGITUDE LINES ARE NOT PARALLELLONGITUDE LINES ARE NOT PARALLEL GEOGRAPHIC NORTHGEOGRAPHIC NORTH

POLEPOLE

GEOGRAPHIC SOUTH POLEGEOGRAPHIC SOUTH POLE

LINES OF LONGITUDELINES OF LONGITUDEARE CALLEDARE CALLEDMERIDIANSMERIDIANS The Prime

MeridianIs located at Greenwich,

England

LLOONNGGIITTUUDDEE

Prime Meridian000

Greenwich, England

Straight lines drawn on Mercator Projections are called RHUMB Lines

On a Mercator Chart,

Rhumb Lines

cross

Meridians of Longitude

at the same angle.

Creating a

LOXODROME

RHUMB LINE

5555

5555

5555

Great CirclesGreat Circles are the shortest

distance between two points. GPSGPS sets always project Great Circle

bearings. All Meridians of Longitude are Great All Meridians of Longitude are Great

CirclesCircles.. All Parallels of Latitude are Small Circles

except the Equator. The intersection of Meridians and

Parallels define a position on the earth’s surface that is called a FIXFIX..

Lambert Conformal Lambert Conformal ProjectionProjection.

Projects the sphere of the earth on a cone.

Charts of the Great Lakes are Conformal Projections.

Aeronautical charts are Conformal Projections.

Conformal projections are more accurate in the northern latitudes.

PolyconicPolyconic

AA

DISTORTION IS MINIMIZED

LINES OF LONGITUDE ARE NOT PARALLEL, BUT CLOSE TO BEINGPARALLELA SPHERICAL SURFACE PROJECTED ON A SERIES OF TANGENTIAL CONES

POLYCONIC PROJECTION

LARGE SCALE CHARTEVERYTHING APPEARS LARGE – more details.

1:1,000 MEANS 1 INCH ON THE CHARTIS 1,000 INCHES ON THEEARTH’S SURFACE.

EVERYTHING APPEARS SMALL – less detail.SMALL SCALE CHART

1:100,000 MEANS 1 INCH ON THE CHARTIS 100,000 INCHES ON THEEARTH’S SURFACE.

A Large Scale Charts

provides

a smaller area

and more details.

San Diego ApproachSmall Scale 1:100,000

1:80,000

Small Scale

1:25,000Large Scale

Coastal Chart 1:40,000 1:150,000

Coastal Chart 1:40,000 1:150,000

Harbor Chart 1:2,000 1:40,000

Chart Orientation TRUE NORTHTRUE NORTH is at the top of the chart.

EASTEAST is at the right-hand side of the chart.

WESTWEST is at the left-hand side of the chart.

SOUTHSOUTH is at the bottom of the chart.

New TerminologyNew Terminology Meridians of LongitudeMeridians of Longitude

– Vertical lines on the chart.– Numbered in degrees eastward and

westward from the Prime Meridian located in Greenwich, England.

– Longitude Scales are found at the top and bottom of a nautical chart.

– Distortion occurs as the Meridians approach the poles.

– Always Great Circles.

Parallels of LatitudeParallels of Latitude [ LAT is FLAT]

– The horizontal lines on a Nautical Chart.

– Numbered in degrees north and south of the equator toward the poles.

– Latitude scales are located at the left and right hand sides of the nautical chart.

– One degree of latitude is equal to 60 nm.

One minute of Latitude is equal to one nm.– Latitude scales are used to measure distance

on a nautical chart.

SC - Small Craft ChartSC - Small Craft Chart The Small Craft Chart is the exception

to the rule.

True North orientation is not at the top of this chart.

Use the Compass Rose to orient True North on a SC Chart.

The Compass RoseThe Compass Rose Every chart has a least one Compass

Rose.

The star on the Compass Rose points to True North.

The outer circle projects True North,

The inner circle projects Magnetic North.

VARIATIONERROR

TRUENORTH

MAGNETICNORTH

COMPASS ROSE

Magnetic North is 016 degrees016 degrees to the West West

in the Boston area. The difference between True and Magnetic

North is called Variation ErrorVariation Error.. Variation ErrorVariation Error is printed in the center of

the Compass Rose. By using the latest charts, you will always

have the latest up-to-date variation references.

Many newer GPS sets automatically adjust for Variation Error. Check your GPS manual!

Chart NumberChart Number Located at the bottom left-hand corner of a

nautical chart.

Chart Number is the official document number for the chart.

Edition Number is also shown.

Date of last Update indicates the last time that the chart was updated was 10:00 AM on this date.

Chart Number and Revision Date

The Coast Guard publishes data for

correcting nautical charts in a free publication called the:LNM - Local Notice to Mariners.

The LNM Internet Address is:

www.navcen.uscg.mil Always use the latest edition charts

for the greatest safety.

General Information General Information BlockBlock

1. The NameName reflects the body of water covered by the chart.

2.2. Vertical DatumVertical Datum - definition of how depths are measured on the chart.

Feet, Meters, or Fathoms (6 feet).

Calibrate your depth sounder to this Datum.

General

Information

Block

1. Name2. Vertical Datum - Depth

MLW - Mean Low WaterMean Low Water - is the

mean or average of the all of the low tide projections for the area.– Boston has two low tides per day.

MLLW - Mean Lower Low WaterMean Lower Low Water is the mean or average of the lowest tide projections for the area.– The lowest of the lows.– All charts are being changed to this

datum.

Cautionary Notes A “Mean” is an average. Therefore,

depths can be higher or lower than the printed depth shown on a nautical chart.

Depths are also affected by storms, the moon, and shoaling in the area.

– Onshore winds can increase the depth of water.

– Offshore winds can decrease the depth of water and/or delay its predicted depth time.

Depths found on nautical charts are best professional guesses.

Always use two methods for determining water depth.– A charted depth and a depth sounder are

acceptable as long as the depth sounder is set to the vertical datum from the chart that you are using.

Before you start out on a trip, always calibrate (verify) the accuracy of your depth sounder.

3.3.Scale of the ChartScale of the Chart - - a ratio of inches on the

chart to inches on the earth’s surface.

– 1:40,000 means that 1 inch on the chart represents 40,000 inches on the earth’s surface.

4.4.Heights of ObjectsHeights of Objects are measured in vertical datum above Mean High Water.

– Clearance under bridges are measured up from the MHW projection.

– Heights of lights are measured up from the MHW projection to the focal plane of the light.

Special Abbreviations and NotesSpecial Abbreviations and Notes are

shown that are peculiar to the area. Cautionary NotesCautionary Notes - special notes of

uncharted dangers in the area. Special Tide and Current InformationSpecial Tide and Current Information -

any unique tide or current phenomena in the area is noted.

Magnetic InterferenceMagnetic Interference in the area. LORAN InterferenceLORAN Interference in the area. Anchorage AreasAnchorage Areas in the area.

Soundings and Water DepthSoundings and Water Depth

Depth designations are shown with:– Numbers which reflect the vertical

sounding datum.– Colors - shallow water is tinted a darker

blue and deeper water is a lighter blue and white.

– Contour Lines - a system of standardized symbols and abbreviations - dots and dashes.

Depths are expressed in:

– Feet.– Meters.– Fathoms [Six Feet per Fathom]

All depths refer to the vertical datum of the chart.

Main DredgedChannel

Redright

returning

from

the

sea

353o True

ColregsDemarcation

Line

Lighthouse

30 foot line

Scale

1:12,000

Aids to NavigationAids to Navigation SymbolsSymbols for ATONs.

– Diamond with a small circle.– Lighted ATONs show a magenta circle and a

small circle.

AbbreviationsAbbreviations for shape of ATONs.– N - designates a nun or conical shaped buoy.– C - designates a can shaped buoy.

Abbreviations that indicate color of

the ATON.R - Red - Diamond symbol will be printed

red.G - Green - Diamond symbol will be

printed green. RRWW - Red and White..GR - Green buoy with Red band.RG - Red buoy with Green band.Y - Yellow - When ATON is painted white

or yellow, the diamond chart symbol is left white or blank.

Abbreviations for Light color on Buoys:

– R - Light is Red.

– G - Light is Green.

– Y - Light is Yellow.– When no color symbol is shown with a buoy,

the light color is assumed to be white. Other Features on Buoys:

– Sound Signals - Horns, whistles, bells, and gongs.

– RADAR Reflectors - reference is found only in the Light List.

– Numbers - Nuns are even numbered and cans are odd numbered.

– Letters - Used on non-lateral buoys.

– Light Flash Characteristics - how the light flashes.

Note: The numbers or letters, and the flashing characteristics on the Aid are printed on the nautical chart beside the chart symbol.

Symbols for Light Houses and

Other Fixed Aids.

–Major Lights - Light Houses. Black Dot with a Flare - looks like an

exclamation point. Name of Light appears on the Chart. Shows height and range of light.

–Small Lights - Fixed Lights. Black Dot with a Flare - looks like an

exclamation point. Not named on the chart. Will show height and range.

Portland Head

Brenton Reef Light

No

longer

exists

Ranges:

– Consist of two daymarks or beacons.– Shows a dashed line in the direction of the

range or safe water.– If not lighted, shows daymark symbols as

squares or triangles.– Interpretation of panel colors is found in the

front of the Light List.– If lighted, light symbols and flash

characteristic appears on the chart.

CAUTIONARY NOTE: Ranges are usually fixed on land, rocks, or shoals. Always use a nautical chart when transiting a range.

RANGE

Shelter Island Range, San Diego

Range

Isolated Danger Marks

– Erected on or moored over a danger.– Horizontal bands of red and black.– White light.– Top mark of two black spheres.– Chart symbol has two black dots over

the diamond symbol.

Daymarks - Day Beacons

– Permanently fixed structures.– Uses square, octagonal or triangle panels to

designate their use.– TR and small triangle.

Red - Even numbered - Red light if lighted. Treat as if a nun buoy

– SQ and small square. Green - Odd numbered - Green light if

lighted.

CAUTIONARY NOTE: Do not pass close aboard (near) daymarks due to the danger of striking their foundation.

Other Charted Features

Prominent Landmarks– Water towers, smoke stacks, church

spires, flag poles, public buildings.– Symbol is a circle with a dot indicating a

highly surveyed position.– Great for taking bearings.– Circle symbol without a center dot is an

approximate position.– Landmarks on private property are not

plotted on nautical charts.

Wrecks, Rocks and Reefs.

– May be shown as: Symbol Abbreviation plus a number. Dashed or dotted line around a symbol.

Bottom characteristics– Symbol or abbreviation used alone or in

combination.Structures

– Jetties, docks drawbridges, and ramps.– Some docks do not appear on a chart

depending on the scale of the chart.

ROCKs and Obstructions

BRIDGES

Coastlines– Identified at both high and low water.– Any prominent landmarks that may help you

get a fix on your position may be shown.– Any details located a short distance from the

shore line may not be shown.

Lettering on a Nautical Chart.– Vertical lettering indicates fixed objects.– Slanted lettering indicates floating objects.

Horizontal Datum Accuracy is based on the survey that was made

to generate the chart.– NAD27– NAD83

WGS84 Has accuracy impact between your GPS Set and the

nautical chart..

Your GPS set must be adjusted to reflectthe datum of the Nautical Chart that youare using.

Criteria used to determine the accuracy of

a nautical chart..

– Source and date of the survey.

– Amount of detail of the soundings in an area.

– Blank spaces should be regarded with suspicion.

– The term, “Dumping Ground”, indicates that material was dumped in the area and that soundings in this area have not been verified.

Effect of the NAD83 Datum shifts in Latitude and Longitude.– Great Lakes - 15 yards.– Atlantic Coast - 35 yards.– Gulf of Mexico - 35 yards.– Pacific Coast - 100 yards.– Hawaii - 500 yards.– Alaska - 500 yards.– Puerto Rico - 240 yards.

Any Questions? Mercator Projection Small Craft Chart Compass Rose General Information Block Mean Lower Low Water. Vertical Datum – Depth. Horizontal Datum – Area.

Electronic Equipment Notes

Set your Depth Sounder to the vertical datum from your chart—feet, meters, or fathoms.

Set your GPS to the horizontal datum from your chart--WGS 84.

If your GPS or LORAN does not have an automatic variation adjustment, set it for the Variation Error found in the nearest Compass Rose.

Traffic Separation Scheme

Any questions about:

AV Task 1-3 Making LNM corrections to a nautical chart –

page 117