The noise escaping from the exhaust chimneys of the naval constructions is characterized by the firing frequency in the 31.5 Hz or lower band and can be perceivable and annoying to the open bridges. Although the global level in dB (A) is within the limits, it is desired to reduce the sound pressure level in particular at the frequency indicated above also for improvements to existing ships.
CTM Ambiente has studied a solution that consists of replacing the final section of the chimney with a resonator silencer of the same length and diameter that attenuates the sound pressure as specified below.
It guarantees a reduction in noise from the chimneys of at least 10 dB in the 31.5 Hz band. The measurement of attenuation is carried out, with instrumentation certified IEC cl. 1, in the same position on the open bridge and in the same operating conditions of the engines
During the test the background noise, including that coming from other parts of the same system (such as the noise produced by the machine fans) must be irrelevant or it must be taken into account with the method established by the ISO standard.
The pressure loss introduced by the additional silencer is negligible at the design conditions.