A Nautical Chart is a graphic portrayal of the marine environment. In addition to its basic elements, a chart is a working document used by the mariner both as a "road map" and worksheet and is essential for safe navigation. In conjunction with supplemental navigational aids, it is used to lay out courses and navigate ships by the shortest and most economical safe route. A chart shows the nature and form of the coast, the depths of the water and general character and configuration of the sea bottom, locations of dangers to navigation, the rise and fall of the tides, locations of man-made aids to navigation, and the characteristics of the Earth's magnetism.
Nautical charts are based on hydrographic surveys. As surveying is laborious and time-consuming, hydrographic data for many areas of sea may be dated and not always reliable. Depths are measured in a variety of ways. Historically the sounding line was used. In modern times, echo sounding is used for measuring the seabed in the open sea. When measuring the safe depth of water over an entire obstruction, such as a shipwreck, the minimum depth is checked by sweeping the area with a length of horizontal wire. This ensures that difficult to find projections, such as masts, do not present a danger to vessels navigating over the obstruction.
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Most of local navigators in the area rely on natural navigation, you might wonder why Nautical Charts are rarely used by boat captains. The reason stand behind is local boat captains are very familiar with reef formations and their positions in their area, most of them still even refuse to use the modern navigation tools such as GPS (Global Positioning System) however, boat captains and dive guides should be able to read the Nautical Charts.
By reading nautical charts properly, you will have useful information on position of moorings, lighthouses, existing reef banks, depth, natural bays and ports.
Defining the route in safety, especially for distant destinations or navigating during night is only possible with the help of a nautical chart.