Annex 3

• 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 180-700Hz (± 1%) for a vessel of 20 m or more in length, or 180-2100 Hz(±1%) for a vessel of less than 20 m in length and which provide the sound pressure levels specified in paragraph 1 (c) below.
• 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 m or more in length;

  (ii) 130-350 Hz, for a vessel 75 m but less than 200 m in length;

  (iii) 250-700 Hz, for a vessel less than 75 m in length.
• A whistle fitted in a vessel shall provide, in the direction of maximum intensity of the whistle and at a distance of 1 m from it, a sound pressure level in at least one 1/3-octave band within the range of frequencies 180-700 Hz (± 1%) for a vessel of 20 m or more in length, or 180-2100 Hz (±1%) for a vessel of less than 20 m in length, of not less than the appropriate figure given in the table below.

  
• 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% 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 500 Hz).
• The sound pressure level of a directional whistle shall be not more than 4 dB below the prescribed sound pressure level on the axis at any direction in the horizontal plane within ± 45° on the axis. The sound pressure level at any other direction in the horizontal plane shall be not more than 10 dB below the prescribed sound pressure level on the axis, so that the range in any direction will be at least half the range on the forward axis. The sound pressure level shall be measured in that 1/3-octave band which determines the audibility range.
• When a directional whistle is to be used as the only whistle on a vessel, it shall be installed with its maximum intensity directed straight ahead.
• A whistle shall be placed as high as practicable on a vessel, in order to reduce interception of the emitted sound by obstructions and also to minimize hearing damage risk to personnel. The sound pressure level of the vessel's own signal at listening posts shall not exceed 110 dB (A) and so far as practicable should not exceed 100 dB (A).
• If whistles are fitted at a distance apart of more than 100 metres, if shall be so arranged that they are not sounded simultaneously.
• Combined whistle system


  1. Whistles located at a distance apart of not more than 100 m

  2. Whistles arranged to be sounded simultaneously

  3. Frequency of any one whistle shall differ from those of the others by at least 10 Hz
• Combined whistle system

  Regarded as a single whistle for the purposes of the Rules
• Due to the presence of obstructions the sound field of a single whistle or of one of the whistles referred to in paragraph 1 (f) above is likely to have a zone of greatly reduced signal level


  It is recommended that a combined whistle system be fitted so as to overcome this reduction
• (a) Intensity of signal

  A bell or gong, or other device having similar sound characteristics shall produce a sound pressure level of not less than 110 dB at a distance of 1 m from it.
• (b) Construction

  Bells and gongs shall be made of corrosion-resistant material and designed to give a clear tone. The diameter of the mouth of the bell shall be not less than 300 mm, for vessels of 20 m or more in length. Where practicable, a power-driven bell striker is recommended to ensure constant force but manual operation shall be possible. The mass of the striker shall be not less than 3% of the mass of the bell.
• The construction of sound signal appliances, their performance and their installation on board the vessel shall be to the satisfaction of the appropriate authority of the State whose flag the vessel is entitled to fly.