"1. Whistles
(a) Frequencies and range of audibility
The fundamental frequency of the signal shall lie
within the range 70-700 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 range
180-700 Hz (± 1 per cent), 180-2100 Hz (± 1 per
cent) for a vessel less than 20 metres in length, and
which provide the sound pressure levels specified in
paragraph 1(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) 70-200 Hz,for a vessel 200 metres or more in
length;
(ii) 130-350 Hz, for a vessel 75 metres but less
than 200 metres in length;
(iii) 250-700 Hz, for a vessel less than 75 metres
in length.
(c) Sound signal intensity and range of audibility
A whistle fitted in a vessel shall 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 180-700 Hz (± 1 per cent), 180-2100
Hz (± 1 per cent) for a vessel less than 20 metres
in length, of not less than the appropriate figure
given in the table below.
*1When the measured frequencies lie within the range
180-450 Hz
*2When the measured frequencies lie within the range
450-800 Hz
*3When the measured frequencies lie within the range
800-2100 Hz
Bold = New added text
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
250 Hz 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.
to (g):No Change"
I:/MSC/69/20-4
