Seaman's Handbook

ANNEX III. Technical details of sound signalling appliances

(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 metre from it.(b) Construction Bells and gongs shall be made of corrosion resistant materials 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 metres or more in length. Where practicable, a powerdriven 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 per cent of the mass of the bell.