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Noise from ships in ports. Possibilities for noise reduction

2 Noise from ships in ports

• 2.1 Existing legislation on external noise
  • 2.1.1 Calculation example 1: Maximum allowable noise from the diesel generator exhaust

Ship operations in ports occasionally cause problems with disturbing noise in nearby dwellings. The rules and regulations of noise from ports have not been as explicit as in other areas of industry and commerce. With the increasing desire for planning denser cities and in particular the demand to convert deserted harbour areas into attractive dwelling areas the need for clear rules has increased. In this context it is important to disseminate information about the relevant noise sources and the possibilities for control of these. In recent years several EU funded projects have been or are being carried out with special attention to harbour noise and noise from ships e.g., NoMEPorts (Noise Management in European Ports), [1], and BESST (Breakthrough in European Ship and Shipbuilding Technologies). Therefore, future additional external noise requirements for ships are an obvious possibility.

2.1 Existing legislation on external noise

The international maritime organisation, IMO, specifies in resolution A.468(XII), Code on noise levels on board ships, [2] and [3], a noise limit of 70 dB(A) at listening posts, including navigating bridge wings and windows during the ship’s normal operational conditions. The Danish Maritime Authority has, in addition to the IMO resolution, noise limits and recommended limits at listening posts, external leisure areas and rescue stations stated in their Technical Regulation on Noise in Ships, [4]. These noise limits are 70 dB(A) at listening stations and 75 dB(A) at external leisure areas and rescue stations; recommended limits are 5 dB lower. New ships should be designed to have noise levels below the recommended noise limit. These limits restrict the total noise level at listening posts and other positions which indirectly limit how much noise commercial ships may cause in the surroundings.

In addition to the IMO resolution there may be national legislation on noise limits in the harbour area. For example Danish legislation specifies that the whole harbour, including ships at berth, should be treated as an “industrial source” with noise guideline limits as defined by the Danish Environmental Protection Agency in [5]. However, this legislation only applies to ship at berth and not during manoeuvring in the port. With regard to noise this is the most interesting period as the time at berth is usually significantly longer than the manoeuvring time in port. An excerpt of the guiding limits is given in Table 1. The limits are quite strict especially if the ship is at berth close to residential or recreational areas.

Furthermore, the Danish Environmental Protection Agency, has guiding limits for the highest allowable low frequency noise in nearby dwellings, [6].

Similar limits for low frequency noise are part of a mandatory licensing scheme for high speed ferries operating from Danish ports. The system was introduced after a new fast ferry route was established between Copenhagen ports, Århus and Kalundborg in Denmark, see [7]. This gave rise to several complaints due to the low frequency noise caused by the fast ferries.

2.1.1 Calculation example 1: Maximum allowable noise from the diesel generator exhaust

Consider a container ship equipped with one diesel generator and one main engine with exhaust outlets at 20 m distance from a listening post, see Figure 1.

Figure 1 Sound pressure level calculation at the listening post.

The noise limit at the listening post, as defined by IMO regulations, is 70 dB(A) at a normal sailing condition. This imposes limits on the maximum allowable sound power of the diesel generator and the main engine exhausts.

The most basic propagation model describes the sound pressure level at a receiving position at a large distance from a noise source. The equation is shown below:

L_p: Sound pressure level in the receiving position, dB re. 20µPa

L_w: Sound power level of source, dB re. 1pW

r: The distance between the source and receiver, m

The above equation assumes spherical noise propagation in the free field i.e. that there are no reflections and attenuation is only due to spherical spreading with distance.

By applying the IMO noise limit and the above equation the maximum allowable total sound power of the main engine and diesel generator exhaust outlets can be calculated to 107 dB(A).

During berth only the diesel generator is in operation in order to generate electrical power onboard the ship. The main engine is stopped. The distances from the noise source that are required to fulfil the noise guiding limits in Table 1 can likewise be calculated by applying Eq.1.

As a worst case scenario a diesel generator exhaust sound power level of 107 dB(A) is adopted. This corresponds to the case where the diesel generator exhaust noise is considerably higher than the noise from the main engine.

The limits and calculated distances from the noise source in order to meet these limits are given in the table below:

The distances from the ship required to fulfil the guiding limits are seen to be quite large especially if recreational areas are considered in the vicinity of the port berth.

The above calculation is radically simplified as a number of factors have not been taken into account. These are factors such as screening, reflection and absorption from buildings and surfaces, meteorological conditions, directivity of the noise sources, etc. A more accurate calculation of the noise caused by a ship in the surroundings can be performed by applying different standards for calculating the noise propagation such as the Danish environmental guideline no. 5/1993, [8]. Different standards and methods for calculating the environmental noise from ships, industries etc. are included in different software tools such as ‘SoundPLAN’, ‘Predictor’ and ‘CadnaA’

It can be concluded that a ship in port that fulfils the IMO resolution can easily excess the Danish Environmental Agency guiding noise limits if at berth in the near vicinity of residential areas.

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Version 1.0 June 2010, © Danish Environmental Protection Agency