CFR

86.05—Sound signal intensity and range of audibility.

A whistle on a vessel shall provide, in the direction of the forward axis of the whistle and at a distance of 1 meter from it, a sound pressure level in at least one 1/3 -octave band of not less than the appropriate figure given in Table 86.05 within the following frequency ranges (±1 percent):

(a) 130-1200 Hz, for a vessel 75 meters or more in length;

(b) 250-1600 Hz, for a vessel 20 meters but less than 75 meters in length;

Table 86.05

Length of vessel in meters	Fundamental frequency range (Hz)	For measured frequencies (Hz)	1/3-octave band level at 1 meter in dB referred to 2×10 −5 N/m2	Audibility range in nautical miles
		130-180	145
200 or more	70-200	180-250	143	2
		250-1200	140
		130-180	140
75 but less than 200	130-350	180-250	138	1.5
		250-1200	134
		250-450	130
20 but less than 75	250-525	450-800	125	1.0
		800-1600	121
		250-450	120
12 but less than 20	250-525	450-800	115	0.5
		800-2100	111
Note. The range of audibility in the table above is for information and is approximately the range at which a whistle may usually be heard on its forward axis in conditions of still air on board a vessel having average background noise level at the listening posts (taken to be 68 dB in the octave band centered on 250 Hz and 63 dB in the octave band centered on 500 Hz).
In practice the range at which a whistle may be heard is extremely variable and depends critically on weather conditions; the values given can be regarded as typical but under conditions of strong wind or high ambient noise level at the listening post the range may be much reduced.

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