(a) A vessel of 12 metres or more in length shall
be provided with a whistle, a vessel of 20 metres or more in length
shall be provided with a bell in addition to a whistle, and a vessel
of 100 metres or more in length shall, in addition, be provided with
a gong, the tone and sound of which cannot be confused with that of
the bell. The whistle, bell and gong shall comply with the specification
in Annex III to these regulations.
The bell or gong or both may be replaced by other equipment having
the same respective sound characteristics, provided that manual sounding
of the required signals shall always be possible.
(b) A vessel of less than 12 metres in length
shall not be obliged to carry the sound signalling appliances prescribed
in paragraph (a) of this Rule but if she does not, she shall be provided
with some other means of making an efficient sound signal.