33 CFR 86.05 - Sound signal intensity and range of audibility.

§ 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;
(c) 250-2100 Hz, for a vessel 12 meters but less than 20 meters in length.
Table 86.05
Length of vessel in meters Fundamentalfrequency range (Hz) For measuredfrequencies (Hz) 1/3-octave band level at 1 meter in dB referred to 2×10 −5 N/m2 Audibility range in nautical miles
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.
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
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