33 CFR 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.
(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.
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 published on 2013-07-01
no entries appear in the Federal Register after this date.