33 C.F.R. § 86.13 Combined whistle systems.
Title 33 - Navigation and Navigable Waters
(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 in §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.
Title 33: Navigation and Navigable Waters
PART 86—ANNEX III: TECHNICAL DETAILS OF SOUND SIGNAL APPLIANCES
Subpart A—Whistles
§ 86.13 Combined whistle systems.
