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Session II Nautical Charts

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1 Session II Nautical Charts

2 Objectives 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

3 One Minute of Latitude equals One Nautical Mile


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

6 1:80,000 Small Scale 1:25,000 Large Scale

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

8 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.

9 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.

10 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.


12 Variation Error is printed in the center of the Compass Rose.
Magnetic North is 013 degrees to the West in the New York area. The difference between True and Magnetic North is called Variation Error. Variation changes yearly. Variation Error is printed in the center of the Compass Rose. Many newer GPS units automatically adjust for Variation Error. Check your GPS manual!

13 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.

14 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.

15 Horizontal Datum Update your GPS with the HORIZONTAL DATUM referenced on the nautical chart that you are using. WGS84 Refer to the General Information Block on your Nautical Chart for the horizontal datum. Have a backup on Datum handy. I had a question and needed to speak to it.

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

17 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.

18 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.

19 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. 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.

20 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.

21 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.

22 Depths are expressed in:
Feet. Meters. Fathoms [Six Feet per Fathom] All depths refer to the vertical datum of the chart.

23 Aids to Navigation Symbols for floating buoys.
Diamond with a small circle. Lighted ATONs show a magenta circle and a small circle. Abbreviations for shape of buoys. N - designates a nun or conical shaped buoy. C - designates a can shaped buoy.

24 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.

25 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.

26 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.

27 Chart Symbols CAN - Green Diamond with
small watch circle NUN – Red diamond with small watch circle. Watch circle overprinted with magenta when lighted. Italics used for buoys and other floating aids.

28 Symbols - Daymarks and Minor Lights
Green Daymark Green square. Red Daymark Red triangle Minor Light - Magenta exclamation mark (teardrop) with black dot Vertical letters used for fixed marks



31 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.

32 Fixed Aids Small Light Major Light

33 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.


35 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.

36 Daymarks - Day Beacons TR and small triangle. SQ and small square.
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.

37 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.

38 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.


40 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.

41 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.

42 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.

43 Chart Corrections Local Notice to Mariners found on internet Always start with the most recent LNM and work backwards Temporary corrections are made in pencil Permanent corrects are done in ink

44 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.

45 End of Session II

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