Annex III specifies the frequency, sound pressure, directional properties, and positioning requirements for whistles, bells and gongs. Whistles shall be heard at specific distances based on vessel length. Fundamental frequency: 70–700 Hz for vessels ≥ 200 m, 130–700 Hz for 75–200 m, 250–700 Hz for smaller vessels.
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Annex III – Technical Details of Sound Signal Appliances
Plain-language COLREGS reference with the complete rule text and practical clause breakdown.
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