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).
Rules and Regulations
Acoustic Insulation
| 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.