Underwater ship passport

For years in the Polish Navy extensive measurements have been made of the underwater-radiated noise by different kinds of surface ships. To identify the source of noise, the level of vibration was also measured by accelerometers inside each ship section. Radiation at discrete frequencies caused by low frequency hull vibrations, excited by the machinery is easily detected and must be reduced as much as possible. The radiated noise spectra show high-level tonal frequencies from propellers and main engines. They varied with speed of the vessel in a complex manner. Ship 's service diesel generator (SSDG) creates a series of harmonies which amplitudes and frequencies are independent of ship speed. The articles documents series characteristics of the surface ship's radiated underwater noise data. The noise from small vessels elevates the natural ambient noise by 10-40 dB. Third-octave bandwidth analyses are too wide separation of the individual radiated components of ship noise that 's why accurate narrow-band spectra (sometimes less than 0,1 Hz) have been made