Knowledge Base
Noise Emitted by Secondary Machinery
Noise (air- borne and structure- borne noise) emitted by secondary machinery becomes very important especially at anchor condition. In case correct measures are taken into account related to noise emitted by the generator set (sound shield and mounting system) and air conditioning (as mentioned in this document) low noise levels can easily be achieved in cabins and rooms.
The next level is to take care of secondary machinery such as pumps, fans, toilet systems (very important), zero speed stabilizers etc. Proper mounting system (vertical natural frequency approx. 10Hz) and the location (preferable Engine Room) is essential.
From the previous diagram (load versus deflection) a correct mount can be selected. Recommended is approx. 10 Hz natural frequency equal to approx. 3 mm deflection (Fz = SQR (300 / deflection). So, pending on the load various shore hardness can be selected to choose the correct mount. If the mount is too soft too much deflection can be expected which can cause problems, too stiff means not enough isolation ending up with too much structure- borne noise / vibrations in the ship structure.
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In some cases secondary machinery is located underneath the sole in accommodation areas. Selecting a correct mount is not sufficient as air- borne noise is also a dominant factor. In this case a sound shield around the secondary machinery could be the solution or a proper sound reducing sole panel (sound reducing sandwich panel).
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