Navigation General · Chart Symbols
On a nautical chart, a light described as 'Fl(2) W 10s 25ft 8M' means the light:
- AFlashes twice (group flashing), white, with a period of 10 seconds, 25 feet above mean high water, nominal range 8 nautical miles✓ Correct
- BFlashes twice, white, with a period of 10 seconds, 25 feet above the sounding datum (MLLW), visible 8 nautical miles
- CIs a fixed white light at 25 feet with 10-second intervals and 8-mile nominal range
- DFlashes white every 2 seconds, 10 times per minute, 25 feet above sea level
Explanation
The light characteristic notation reads: Fl(2) = group flashing, two flashes; W = white; 10s = period of 10 seconds (one full cycle); 25ft = focal-plane height above mean high water (MHW); 8M = nominal range of 8 nautical miles. On U.S. charts, heights of lights and clearances use the high-water datum (MHW), while charted depths/soundings use the low-water datum (MLLW).
Authority: Chart No. 1, Section P
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