Rules and Regulations

Acoustic Insulation

In general for commercial vessels the rules concerning noise levels onboard are quite simple and few. It is basically a set of dB(A) levels given for a range of different positions onboard. These settings are given in the IMO res. A. 468(XII).

Limits for noise levels are specified for various maximum spaces as follows:
Work spaces db(A)
Machinery spaces (continously manned) 90
Machinery spaces (not continously manned) 110
Machinery control rooms 75
Workshops 85
Non-specified work spaces 90
Navigation spaces db(A)
Navigation bridge and chart rooms 65
Listening posts, including navigation bridge wings and windows 70
Radio rooms (with radio equipment operating but not producing audio signals) 60
Radar rooms 65
Accommodation spaces db(A)
Cabins and hospitals 60
Mess rooms 65
Recreation rooms 65
Open recreation areas 75
Offices 65
Service spaces db(A)
Galleys, without food processing equipment 75
Service and pantries 75

 

Normally unoccupied spaces db(A)
Spaces not specified 90

When the sound hits a wall, the sound is reflected - some will be absorbed and a small part will be transmitted.

The sound insulation property of the construction, its reduction power called R, is measured in dB and is a measurement of the power of the construction to prevent the passage of the sound.

High R = good sound insulation = good sound reduction

In porous absorbers like ROCKWOOL materials the sound absorption takes place by the sound energy being converted into frictional heat between the ROCKWOOL fibres. The sound absorption depends on the thickness of the material. The values at the low frequencies are improved with increased thickness. The same tendency can be obtained by moving the absorbers away from the base.

Protection of the absorber by a cover plate does not change the absorption as long as the plate has a sufficient number of openings. A perforation of 15% could be sufficient for a 1 mm thick cover plate of steel. Thicker covers require a large number of small holes.