Today is the second of a series of articles about Navigation. You can advance your Navigation Know How by participating in the Nautical Know How Coastal Navigation Course.
These basics are covered in the online Nautical Know How Basic Boating Safety Course at http://boatsafe.com/navigation .
Nautical charts are different from maps in that they specifically depict water areas while maps concentrate on land area, roads, landmarks, etc. Land areas and features on charts are sketchy and are noted only for their interest to the Navigator. Unlike maps, the nautical chart conveys much information specifically designed to assist in safely navigating the area that the chart covers.
Chart Scaling
The scale of a chart is expressed as a ratio such as 1:80,000. This could also be represented as the fraction 1/80,000. This means that one unit on the chart represents 80,000 of the same units on the earth. The terms “small scale” and “large scale” can be confusing if you haven’t studied fractions recently. The denominator of the fraction (the number under the line) is the number that changes as the scale of the chart changes. The larger the denominator the smaller the fraction. For instance 1:80,000 is smaller than 1:40,000, so the larger the denominator the smaller the scale of the chart. That is, a 1:80,000 chart would be a small scale while a 1:40,000 would be a large scale.
Chart Colors
The major water areas are not colored and retain the white color of the paper itself. Shallow water areas, shown in light blue and light green, indicate shallows that are uncovered at some stage of the tide, such as marsh areas.
Small objects such as buoys and markers are shown in a magenta color. Because charts are used at night under red light (to keep from impairing night vision) the color magenta shows up best at night and in the day.
Buoys and dayboards that are actually red are indicated in magenta. Green buoys and dayboards are shown in green.
Lighted buoys, regardless of their color, are shown with a magenta dot over the small circle portion of the chart symbol. Cautions, symbols noting danger, compass roses and recommended courses are also noted in magenta.
For more about the Nautical Know How Coastal Navigation Course…READ MORE.
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