33 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):
|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.|
|200 or more||70-200||180-250||143||2|
|75 but less than 200||130-350||180-250||138||1.5|
|20 but less than 75||250-525||450-800||125||1.0|
|12 but less than 20||250-525||450-800||115||0.5|
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