Session II Nautical Charts

1
Session IINautical Charts
2
Objectives

• To become familiar with
• data found on Nautical Chart and how it relates
  to GPS and the AtoN Program.
• how depths are depicted on a chart.
• the horizontal and vertical datum on chart

3
Expectation You as members of Auxiliary are
familiar with or will become familiar with the
information on a chart.
4
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.

5

• Depth Soundings
• 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.
• Always calibrate (verify) the accuracy of your
  depth sounder.

6

• Heights of Objects are measured in vertical
  datum above Mean High Water (MHW).
• 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.

7
Electronic Equipment Notes

• Set your Depth Sounder to the vertical datum from
  your chartfeet, 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.

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End
of
Session II