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| Nautical charts are maps of the sea. For a defined area, a chart shows the nature and form of the coast, the depths of the water and general layout of the ocean floor, navigational hazards and aids, and the characteristics of the Earth's magnetism. They are basically road maps that enable boats to plan and plot safe courses. All commercial vessels are required to have nautical charts on board when boating coastal waters, and it is recommended that recreational boaters use charts as well. | ||
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Scale is the relationship between distance on the chart and actual distance on the water. Generally,
it is given as a fraction or ratio, such as 1:250,000 or 1:10,000. The first number represents the
chart distance, and is always 1. The second number represents the actual distance and is different
for each scale. Here's where it gets confusing -- the larger the second number, the smaller the scale
of the chart.
Actually, it makes sense. Fox example, one inch on a 1:10,000 scale chart represents 10,000 inches on the water. This is considered a large-scale chart, and it shows the most detail. If the scale of the chart is reduced to 1:10,000,000, then one inch on the chart will equal 10,000,000 inches on the water -- a small-scale chart. Since the small-scale chart must depict a much larger area, many of the details shown on a larger-scale chart are omitted. The vast majority of nautical charts are between 1:40,000 and 1:200,000. |
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Small-scale nautical chart (1:80,000) View larger image |
Large-scale nautical chart (1:25,000) View larger image |
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In 1807, President Thomas Jefferson created the Survey of the Coast "...to cause a survey to be taken of coasts of the United States, in which shall be designated the island and shoals and places of anchorage...". A Swiss mathmetician and geologist named Ferdinand Hassler was named as Superintendent of the new bureau, and he set about the daunting task of surveying and charting the nation's coastlines. Early nautical charts were designed for shallow-draft wooden sailing ships, which were dependent upon wind and currents for navigation. The modern chart evolved following the invention of the steamer in the early nineteenth century. Unlike sailing ships, steamers could follow any chosen course regardless of wind -- provided it led through adequate depths. As shipbuilding technology progressed, ships increased dramatically in size and draft. Thus, the focus of hydrographic surveys shifted from shoal waters to the deeper nearshore waters and channels. The first nautical chart of Newark Bay was published in 1839, using a stone engraving. By 1842, a coppper-plate printing press had been acquired, allowing much finer detail than the stone engraver. The first chart of New York Bay and Harbor was produced using the copper press in 1844. Today, the Coast Survey is a division of NOAA and uses modern computer and satellite technology to produce new editions of nautical charts. |
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