Seaman's Handbook
PART C. Lights and Shapes : Equipment for sound signals
(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 specifications 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
prescribed 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.
