Session II Nautical Charts Objectives F To become familiar with: – data found on Nautical Chart and how it relates to GPS and the AtoN Program. –the.

Session IISession IINautical ChartsNautical Charts

ObjectivesObjectives To become familiar with:

– data found on Nautical Chart and how it relates to GPS and the AtoN Program.

– the compass rose and variation error.

– The General Information Block

– how depths are depicted on a chart.

– the symbols and abbreviations on a chart.

– the scale of a nautical chart.

– the horizontal and vertical datum on chart

One Minute

of

Latitude

equals

One Nautical Mile

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.

1:80,000

Small Scale

1:25,000Large Scale

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.

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.

VARIATION

ERROR

TRUE

NORTH

MAGNETIC

NORTH

COMPASS ROSE

Magnetic North is 013 degrees013 degrees to the West West

in the New York area. The difference between True and Magnetic

North is called Variation ErrorVariation Error. . Variation changes yearly.

Variation ErrorVariation Error is printed in the center of the Compass Rose.

Many newer GPS units 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.

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.

15

Horizontal DatumHorizontal Datum

Refer to the General Information Block on

your Nautical Chart for the horizontal datum.

Update your GPS with the HORIZONTAL DATUM

referenced on the nautical chart that you are using.

WGS84

MLW - Mean Low WaterMean Low Water - is the mean or average of the all of the low tide projections for the area.

MLLW - Mean Lower Low WaterMean Lower Low Water is the mean or average of the lower tide projections for the area.

– The lowest of the lows per day.– All US 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.

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.

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.

Aids to NavigationAids to Navigation SymbolsSymbols for floating buoys.

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

small circle.

AbbreviationsAbbreviations for shape of buoys.– 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.RWRW = 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.

CAN - Green Diamond withsmall watch circle

NUN – Red diamond with small watch circle.

Watch circle overprinted with magenta when lighted.

Italics used for buoys and other floating aids.

Chart Symbols

Symbols - Daymarks and Minor Lights

Minor Light - Magenta exclamation mark

(teardrop) with black dotVertical letters used for

fixed marks

Green Daymark

Green square.

Red Daymark

Red triangle

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.

32

Fixed AidsFixed Aids

Small Light Major Light

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

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.

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 and location is based on the survey

that was made to generate the chart.– NAD27– NAD83– WGS-84

The datum has a major accuracy impact between your GPS Set and the nautical chart..

Your GPS set must be adjusted to reflect

the datum of the Nautical Chart that you

are using.

Criteria used to determine the accuracy of a nautical chart..

– Source and date of the survey – and technology used at that time.

– 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.

Local Notice to Mariners found on internethttp://www.navcen.uscg.gov/LNM/default.htm

Always start with the most recent LNM and work backwards

Temporary corrections are made in pencil Permanent corrects are done in ink

Chart CorrectionsChart Corrections

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– usually WGS 84 in the US.

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

End

of Session II