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86.01 Frequencies and range of audibility
The fundamental frequency of the signal shall lie within the range 70-525 Hz. The range of audibility of the signal from a whistle shall be determined by those frequencies, which may include the fundamental and/or one or more higher frequencies, which lie within the frequency ranges and provide the sound pressure levels specified in 86.05.

86.03 Limits of fundamental frequencies
To ensure a wide variety of whistle characteristics, the fundamental frequency of a whistle shall be between the following limits:
(a) 70-200 Hz, for a vessel 200 meters or more in length;
(b) 130-350 Hz, for a vessel 75 meters but less than 200 meters in length;
(c) 250-525 Hz, for a vessel less than 75 meters in length.

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.

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 2x10-5 N/M2 Audibility range in Nautical Miles
200 or more 70-200 130-180
75 but less than 200 130-350 130-180
20 but less than 75 250-525 250-450
12 but less than 20 250-525 250-450

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.

86.07 Directional properties
The sound pressure level of a directional whistle shall be not more than 4 dB below the sound pressure level specified in 86.05 in any direction in the horizontal plane within + 45 degrees of the forward axis. The sound pressure level of the whistle in any other direction in the horizontal plane shall not be more than 10 dB less than the sound pressure level specified for the forward axis, so that the range of audibility in any direction will be at least half the range required on the forward axis. The sound pressure level shall be measured in that one-third octave band which determines the audibility range.

86.09 Positioning of whistles
(a) When a directional whistle is to be used as the only whistle on the vessel and is permanently installed, it shall be installed with its forward axis directed forward.
(b) A whistle shall be placed as high as practicable on a vessel, in order to reduce interception of the emitted sound by obstructions and also to minimize hearing damage risk to personnel. The sound pressure level of the vessel's own signal at listening posts shall not exceed 110 dB(A) and so far as practicable should not exceed 100 dB(A).

86.11 Fitting of more than one whistle
If whistles are fitted at a distance apart of more than 100 meters, they shall not be sounded simultaneously.

86.13 Combined whistle systems
(a) A combined whistle system is a number of whistles (sound emitting sources) operated together. For the purposes of the Rules a combined whistle system is to be regarded as a single whistle. (b) The whistles of a combined system shall:
(1) Be located at a distance apart of not more than 100 meters, (2) Be sounded simultaneously, (3) Each have a fundamental frequency different from those of the others by at least 10 Hz, and (4) Have a tonal characteristic appropriate for the length of vessel which shall be evidenced by at least two-thirds of the whistles in the combined system having fundamental frequencies falling within the limits prescribed in 86.03, or if there are only two whistles in the combined system, by the higher fundamental frequency falling within the limits prescribed 86.03.

NOTE: If due to the presence of obstructions the sound field of a single whistle or of one of the whistles referred to in 86.11 is likely to have a zone of greatly reduced signal level a combined whistle system should be fitted so as to overcome this reduction.

86.15 Towing vessel whistles
A power-driven vessel normally engaged in pushing ahead or towing alongside may, at all times, use a whistle whose characteristic falls within the limits prescribed by 86.03 for the longest customary composite length of the vessel and its tow.

Subpart B - Bell or gong

86.21 Intensity of signal
A bell or gong, or other device having similar sound characteristics shall produce a sound pressure level of not less than 110 dB at 1 meter.

86.23 Construction
Bells and gongs shall be made of corrosion-resistant material and designed to give a clear tone. The diameter of the mouth of the bell shall be not less than 300 mm for vessels of more than 20 meters in length, and shall be not less than 200 mm for vessels of 12 to 20 meters in length. The mass of the striker shall be not less than 3 percent of the mass of the bell. The striker shall be capable of manual operation.

NOTE: When practicable, a power-driven bell striker is recommended to ensure constant force.

Subpart C - Approval
86.31 Approval [Reserved]