NOAA Nautical charts promote safe navigation on the water if you know how to read them. Boating safety organizations can teach you what you need to know, like how to read nautical charts. Before you take a class, familiarize yourself with these common chart elements.
The small numbers on a nautical chart are water depths – soundings -at the lowest tide. This helps you determine the closest underwater clearance for your boat.
- fathoms (6 feet)
- meters (3.28 feet)
Large lettering in the top right corner of the chart describes the measurement being used. Subscripts (e.g. 52) show depths in combinations of fathoms and feet (5 fathoms and 2 feet) or decimal meters (5.2 meters).
Rocks, reefs, wrecks, and other hazards are depicted with symbols to explain the type of danger, depth, and other features. Water less than 66 feet deep, show dangers surrounded by a ring of black dots with a blue interior.
More than 40,000 buoys, beacons, and lights mark hazards in US waters. They show safe water areas and depths of dredged channels. Nautical charts depict and explain the purpose of each one.
Charts have different “scales,” to measure distances. In open waters, a small-scale chart (1:100,000 or higher) covers large areas. Closer to shore, there are more shoals and underwater debris requiring a large-scale chart (1:20,000 to 1:80,000) over smaller areas.
Inland lakes and the Intracoastal Waterway chart distances in statute miles, a standard land mile. Most other charts use nautical miles equal to 1.15 statute miles – the length of one minute of latitude. A speed of one nautical mile per hour equals 1 knot.
Additional details about certain features, dangers, restrictions, and warnings are found in chart notes. The bottom corners contain the edition number, publication date, map title, and scale of the chart.
Ready for the chart navigation class?
US National Oceanic and Atmospheric Administration, 2014. How to Read A Nautical Chart, https://www.boatingmag.com/how-to/how-to-read-nautical-chart
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