ANNEX 1
PART A
The draft amendments to ANNEX III, 1 of the International Regulations for Preventing Collisions at Sea, 1972
Underline means the added part
"1. Whistles
(a) Frequencies and range of audibility
The fundamental frequency of the signal shall lie within the range 70-700Hz.
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 range 180- 700Hz (+/-1 per cent), 180-2100Hz (+/-1 per cent) for a vessel less than 20 metres in length and which provide the sound pressure levels specified in paragraph l (c) below.
(b) Limits of fundamental frequencies
To ensure a wide variety of whistle characteristics, the fundamental frequency of a whistle shall be between the following limits:
(i) 70-200Hz, for a vessel 200 metres or more in length;
(ii) 130-350Hz, for a vessel 75 metres but less than 200 metres in length;
(iii) 250-700Hz, for a vessel less than,75 metres in length.
(c) Sound signal intensity and range of audibility
A whistle fitted in a vessel shall be provided, in the direction of maximum intensity of the whistle and at a distance of 1 metre from it, a sound pressure level in at least one 1/3rd-octave band within the range of frequencies 180-700Hz (+/-1 per cent), 180-2100Hz (+/-1 per cent for a vessel less than 20 metres in length, of not less than the appropriate figure given in the table below.
*1 When the measured frequencies lie within the range 180-450Hz
*2 When the measured frequencies lie within the range 450-800Hz
*3 When the measured frequencies lie within the range 800-2100Hz
The range of audibility in the table above is for information and is approximately the range at which a whistle may be heard on its forward axis with 90 per cent probability 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 centred on 250Hz and 63 dB in the octave band centred on 500Hz). 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.
(d) to (f): No change."
