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Fog signal
Buoys & beaconsAdvanced
Magenta sound-wave arcs indicate a horn, bell, whistle, gong, or other fog signal.
What it means
Sound-wave arcs beside an aid indicate a fog signal. A nearby abbreviation or legend identifies its type and may give the rhythm.
Why it matters
Sound bends and echoes in fog, wind, and coastal terrain. Use it as supporting information rather than a precise bearing.