Summary and conclusions

Noise from ships in ports. Possibilities for noise reduction

At the request of the Danish Environmental Protection Agency, (Danish EPA), Lloyd's Register ODS has performed a literature study focusing on noise from ships in port and the possibilities for noise reduction.

As a part of the study it has been established that a ship that is in agreement with the external noise limits imposed by the international maritime organisation, IMO, when the ship at berth, potentially can have a significant impact with respect to noise in the surroundings. A calculation example is presented where it is shown that a ship which fulfils the IMO noise limits can have a diesel generator exhaust sound power of 107 dB(A). The Danish EPA noise guiding limits for residential, city areas in the time period 22-07 is 40 dB(A). By applying the most simple noise propagation model it is demonstrated that if the sound power is 107 dB(A) and the noise limit is 40 dB(A), the ship should be berthed more than 600 m away in order not to exceed the noise limit.

An excerpt of the unattenuated sound powers of some marine diesel engine exhausts and ventilation fans have been presented and found to be quite significant in light of the environmental noise requirements. I.e. the sound power of the engine exhausts vary between 135 to 142 dB(A) and of the ventilation fans between 81 to 110 dB(A). Noise measurements of secondary noise sources such as reefers, cooling containers, show that the sound power of a single reefer is in the range of 90 dB(A). Each time the number of reefers is doubled the sound power increases by 3 dB. Therefore the noise from reefers can be significant.

Standard measures for reducing noise from the major external sources onboard ships have been presented including special noise reducing measures. Some of the presented possible noise reducing measures are listed below:

Standard silencers on the diesel generator exhaust i.e. reflection type, absorption type and combination type silencers.
Utilising the main engine exhaust silencer during port stay for the diesel generator exhaust by rerouting the exhaust.
On shore power supply
Standard methods for reducing noise from ventilation systems onboard a ship including adding mineral wool to fan rooms, cylindrical silencers, baffle silencers and noise reducing louvers.

A cost ranking of the different noise reducing measures has been laid out. The cost ranking is based on whether the installation of the noise reducing measure is considered to be cumbersome and time consuming. This is if the installation can be carried out during regular port stay or should be performed on a shipyard. For example installing new silencers in a diesel generator exhaust stack is a major structural change and is performed at a shipyard which is considered to be costly. Whereas, installing mineral wool in a fan room is simple and can be carried out by the ship’s crew or a contractor during port stay. A noise reducing measure on this scale is therefore considered less costly.