Session 1 Nautical Charts

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.

Objectives 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 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 nautical chart helps you: Another GPS Note: While underway, a paper nautical chart is much easier and safer to use than a GPS chart plotter. Identify any hazards and dangers along your course line. Effectively plot a course on your chart. GPS Note: A nautical chart provides a clearer understanding of the geography of the area where your GPS system is operating.

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 Mercator Projection

Mercator Conformal

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 Prime Meridian The Equator

The Magnetic North Pole 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. The North Pole The Magnetic North Pole THE EARTH as a GLOBE The angular difference from your position on the earth to the North and Magnetic North poles is called: “VARIATION ERROR”

EASTERLY AND WESTERLY VARIATION GEOGRAPHIC NORTH POLE MAGNETIC NORTH POLE WESTERLY VARIATION ANGULAR DIFFERENCE BETWEEN TRUE NORTH AND MAGNETIC NORTH WESTERLY VARIATION

Isogonic Lines 21 E variation 10 W variation 10o E variation Isogonic Lines = lines of the same (iso) magnetic variation. Florida is close to 0 degress variation, the Pacific Northwest about 21 degrees east while the east coast of the US is about 10 degrees west. 10o E variation 0 variation

The North Magnetic Pole moves around.

The Magnetic Pole’s movement throughout the years See how the magnetic pole has moved from 1600 to the present.

NORTHERN HEMISPHERE SOUTHERN HEMISPHERE EASTERN HEMISPHERE WESTERN HEMISPHERE NORTHERN HEMISPHERE SOUTHERN HEMISPHERE

THE GLOBE Form Great Circles Parallels of Latitude Form Small Circles Meridians of Longitude Form Small Circles

LATITUDE WEST of the Prime Meridian, and NORTH of the Equator. New England is located: WEST of the Prime Meridian, and NORTH of the Equator. LATITUDE LATITUDE LINES ARE PARALLEL AND RUN IN TRUE EAST AND TRUE WEST DIRECTIONS 75 90 NORTH POLE LATITUDE IS MEASURED IN DEGREES 60 NORTHERN HEMISPHERE IS NORTH OF THE EQUATOR 45 30 30 DEGREES NORTH LATITUDE 15 15 DEGREES NORTH LATITUDE EQUATOR 15 DEGREES SOUTH LATITUDE 15 30 DEGREES SOUTH LATITUDE SOUTHERN HEMISPHERE IS SOUTH OF THE EQUATOR 30 45 60 ANIMATION 75 90 SOUTH POLE

One Minute of Latitude equals One Nautical Mile

Is located at Greenwich, England LONGITUDE LONGITUDE LINES ARE NOT PARALLEL GEOGRAPHIC NORTH POLE LINES OF LONGITUDE ARE CALLED MERIDIANS The Prime Meridian Is located at Greenwich, England GEOGRAPHIC SOUTH POLE

LONGITUDE

Greenwich, England Prime Meridian 000 The Prime Meridian at Greenwich, England. Note the line is illuminated at night. Prime Meridian 000

Straight lines drawn on Mercator Projections are called RHUMB Lines A great circle route is the shortest distance between two points on the face of the earth.

Meridians of Longitude On a Mercator Chart, Rhumb Lines cross Meridians of Longitude at the same angle.

RHUMB LINE Creating 55 a LOXODROME 55 55 A rhumb line on a mercator projection. 55

Great Circles are the shortest distance between two points. GPS sets always project Great Circle bearings. All Meridians of Longitude are Great Circles. 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 FIX.

Lambert Conformal Projection. 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.

Polyconic

A POLYCONIC PROJECTION DISTORTION IS MINIMIZED LINES OF LONGITUDE ARE NOT PARALLEL, BUT CLOSE TO BEING PARALLEL DISTORTION IS MINIMIZED A SPHERICAL SURFACE PROJECTED ON A SERIES OF TANGENTIAL CONES A

SMALL SCALE CHART LARGE SCALE CHART 1:100,000 EVERYTHING APPEARS SMALL – less detail. 1:100,000 MEANS 1 INCH ON THE CHART IS 100,000 INCHES ON THE EARTH’S SURFACE. LARGE SCALE CHART EVERYTHING APPEARS LARGE – more details. 1:1,000 MEANS 1 INCH ON THE CHART IS 1,000 INCHES ON THE EARTH’S SURFACE.

A Large Scale Charts provides a smaller area and more details.

San Diego Approach Small Scale 1:100,000

1:80,000 Small Scale 1:25,000 Large 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 NORTH is at the top of the chart. EAST is at the right-hand side of the chart. WEST is at the left-hand side of the chart. SOUTH is at the bottom of the chart.

New Terminology Meridians 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 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 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 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.

MAGNETIC NORTH TRUE NORTH VARIATION ERROR COMPASS ROSE

Variation Error is printed in the center of the Compass Rose. Magnetic North is 016 degrees to the West in the Boston area. The difference between True and Magnetic North is called Variation Error. Variation 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 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 Block 1. The Name reflects the body of water covered by the chart. 2. Vertical Datum - definition of how depths are measured on the chart. Feet, Meters, or Fathoms (6 feet). Calibrate your depth sounder to this Datum.

1. Name 2. Vertical Datum - Depth General Information Block

MLW - Mean 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 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. Scale 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. Heights 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 Notes are shown that are peculiar to the area. Cautionary Notes - special notes of uncharted dangers in the area. Special Tide and Current Information - any unique tide or current phenomena in the area is noted. Magnetic Interference in the area. LORAN Interference in the area. Anchorage Areas in the area.

Soundings 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.

Red right returning from the sea Main Dredged Channel

Scale 1:12,000 353o True 30 foot line Colregs Demarcation Line Lighthouse 353o True 30 foot line

Aids to Navigation Symbols for ATONs. Diamond with a small circle. Lighted ATONs show a magenta circle and a small circle. Abbreviations 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. RW - 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. Not named on the chart. Will show height and range.

Portland Head

Brenton Reef Light No longer exists The Brenton Reef Light Tower, although shown on 1210Tr Training Chart, is no longer in existence.

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.

Bottom characteristics Structures 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

Lettering on a Nautical 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 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 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. 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 Traffic Separation Scheme entering the Golden Gate and San Francisco Bay Traffic Separation Scheme

A typical PRECAUTIONARY AREA where several vessel traffic lanes converge. Large ship traffic in these lanes is monitored by the Vessel Traffic Service (VTS) in the area.

It's Not the Ocean That Sinks Ships It's the Hard Stuff Around the Edges

AV Task 1-3 Making LNM corrections to a nautical chart – page 117 Any questions about: AV Task 1-3 Making LNM corrections to a nautical chart – page 117