Abstract
Noise were measured many times in compartments of various types of ships at trial such as tanker, cargo ship, dredger, patrol boat and destroyer. The results of statistical study on the calculated value of a noise rating number, sound levels and spectra may be summarized as follows. 1) The relation between the noise rating number (Loudness Level, Perceived Noise Level, Noise Rating Number) and sound levels A, B and C, was revealed. The result indicated that good correlation was reached between the noise rating number and the sound level A calculated from the original noise spectra. 2) Ship noises are estimated on calculated regression lines or more simply by adding the resppective figure 14 (LL), 15 (PNL), and -3 (NRN) to the indicated value of the sound level A, so ship noises should be measured by weighting A regardless of sound level. 3) In living compartment, noises, largely solidborne, have a spectrum which decreases at an approximate rate of 5dB/oct in inverse proportion to the number of frequencies with the sounds level A rated at about 70±20dB. In an engine room, however, noises have a spectrum in which most o energy is found at middle and high frequencies with the level rated at about 95±10dB.
