Navigation General · Chart Symbols
On a nautical chart, a dashed blue line surrounding a shallow area typically indicates which of the following?
- AThe five-fathom (or ten-meter) depth contour✓ Correct
- BA measured-mile course
- CA submarine cable area
- DA Precautionary Area as defined by COLREGS
Explanation
Blue tinting on U.S. charts highlights shallow water, and the dashed blue contour line marks the boundary of that shaded zone — typically the three-fathom, five-fathom, or ten-meter line depending on chart scale. Submarine cables are shown with a separate dashed line symbol, and measured miles use a different notation.
Authority: Chart No. 1, Section I
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