As explored in Blog 3, growing scientific evidence has linked underwater radiated noise (URN)– an incidental product of shipping activities, to detrimental effects on marine mammals and organisms (Di Iorio & Clark, 2010; McCauley et al., 2017; Williams et al., 2015). Figure 1 shows the typical sources of URN from a shipping vessel. Unless there is a coordinated effort among governments, regulatory bodies, and ship manufacturers, the growing number and size of commercial vessels in our oceans will result in a continued increase in underwater noise pollution in the upcoming decades (Kaplan and Solomon, 2016). Therefore, this blog post will examine several key technological and policy options to reduce URN pollution.

Figure 1: Sources of Underwater radiated noise from a typical marine vessel (Smith & Rigby, 2022).

Reducing URN through technological solutions

In a review of noise reduction methods technology, Smith & Rigby (2022) have concluded that there exist numerous technological solutions have reached a high level of development, that can potentially be broadly implemented in the industry without necessitating further extensive research. Examples include passive vibration isolation mounts, vortex generators and an improved hull form design. The below table summarises several key technologies explored by Smith & Rigby (2022), that have high technology readiness levels (TRL). 

Table 1: Description of maturity of technological solutions to reduce URN, and their estimated Technology Readiness Level (TRL). (extracted from Smith & Rigby, 2022). 

Technology  Site of noise source reduction Description of Maturity  TRL
Vortex Generators Sheet and bubble cavitation, blade-rate noise  Widely used in many industries for controlling flow. Experimental and

numerical studies demonstrate effectiveness for improving wake uniformity

and noise reduction. Performance also demonstrated at full-scale. Effectiveness

and optimal design will be vessel specific and future studies should also

consider the impact of the self-noise of the vortex generator.

 7-9
Propeller boss-cap fin/eco-cap Hub vortex cavitation Widely used and multiple numerical, experimental and full-scale studies demonstrate their effectiveness at reducing or removing hub vortex cavitation. Noise reduction characteristics associated with this have also been confirmed experimentally. 6-7
Passive insolation mounts Machinery Noise Well researched technology and used widely on naval and research vessels 9
Active/hybrid isolation mounts Machinery Noise Extensive research, particularly for naval vessels. Technology is used on

submarines

 9
Acoustic black hole Machinery noise Widely used in many industries (including marine) to reduce vibration

transmission and absorb airborne noise

 9

Low uptake of such technological solutions

However, despite such technological solutions being available to reduce URN pollution at the source, they have argued their uptake by the industry is still very low (Smith & Rigby, 2022). Such a view is also adopted by other researchers (Chou, 2020; Merchant, 2019). 

In explaining this low uptake, the following reasons have been given by several authors: 

  1. The lack of legal regulation denoting noise limits, or an economic incentive for commercial ship operators to reduce their noise pollution, or to adopt noise-reducing measures (Merchant, 2019).   
  2. As acoustic trials are seldom conducted in the shipping industry, there is a lack of sufficient quantitative research evidence in two key areas: 
    1. URN levels produced by various shipping vessels under different operating conditions (Smith & Rigby, 2022). 
    2. Reduction of the noise pollution of shipping vessels after the adoption of specific technological solutions (Smith & Rigby, 2022). 

The challenge in designing policies to reduce noise pollution

Referring to the first point of the lack of international regulation in place to reduce shipping noise pollution at the source, a review of international policies, recommendations, actions and mitigation efforts regarding anthropogenic underwater noise by Chou et al. (2020) have confirmed that while many inter-governmental, government and academic bodies have highlighted the prevalent issue of noise pollution by the shipping industry, underwater noise is still not regulated. 

For instance, the International Maritime Organisation (IMO) has, in 2014, published the  “Guidelines for the reduction of underwater noise from commercial shipping to address adverse impacts on marine life” (IMO, 2014). This document detailed various technological solutions and good practices for shipping vessels to reduce their noise levels. However, it did not include any hard limits or regulations. This is unlike IMO’s regulation of sulphur in 2020, where it enforced a limit of the presence of sulphur in ships’ fuel oil to 0.50%, in a bid to reduce the release of sulphur dioxide into the air (Brynolf et al., 2014; Gilbert et al., 2018).  Furthermore, URN noise pollution is also not included in IMO’s International Convention for the Prevention of Pollution from Ships (MARPOL). 

This lack of such international regulation and policies is related to reason 2, where Merchant (2019) argues that the lack of quantitative data denoting the environmental benefit gained by reducing URN levels, has rendered it difficult for decision-makers to justify the economic cost incurred by implementing quieting solutions. Similarly, for many governments, unilaterally adopting assertive measures (e.g. setting maximum noise output levels), would serve to be a disincentive for shipping companies to use their ports (Merchant, 2019). 

However, the lack of sufficient research has not stopped some countries from taking a precautionary approach to dealing with the issue of URN noise pollution (Chou et al., 2021). For example, the Port of Vancouver, through its EcoAction program has taken an incentive-driven policy approach that aims to reduce URN noise pollution by providing lowered harbour rates for commercial vessels that adopt noise reduction technologies (portvancouver, n.d.). However, such incentive-driven policy approaches remain few (Smith & Rigby, 2022).

Moving forward

Moving forward, given the challenges of governments unilaterally adopting regulatory interventions, an internationally coordinated approach would be more effective in reducing global URN noise pollution (Merchant, 2019). Merchant (2019) offers some suggestions, which include setting requirements for new vessels to adopt ship-quieting technologies, while also developing policies to target reducing the noise output of the noisiest existing vessels. 

To aid this, key quantitative research in the above key areas needs to be done. Additionally, it is also necessary to conduct studies over extended periods to determine the effects of noise reduction on surrounding marine wildlife (Chou et al., 2021). It is only when it has been quantitatively evidenced that the reduction of noise through various noise abatement strategies (e.g. adopting noise-reducing technologies, lowering speeds etc) can lead to benefits for surrounding marine organisms, can more efficient and effective command-and-control approaches (mandatory controls to reduce URN noise pollution) be more readily devised and adopted globally (Merchant, 2019). 

References: 

Brynolf, S., Fridell, E., & Andersson, K. (2014). Environmental assessment of marine fuels: Liquefied natural gas, liquefied biogas, methanol and bio-methanol. Journal of Cleaner Production, 74, 86–95. https://doi.org/10.1016/j.jclepro.2014.03.052

Chou, E., Southall, B. L., Robards, M., & Rosenbaum, H. C. (2021). International policy, recommendations, actions and mitigation efforts of anthropogenic underwater noise. Ocean & Coastal Management, 202, 105427. https://doi.org/10.1016/j.ocecoaman.2020.105427

Di Iorio, L., & Clark, C. W. (2010). Exposure to seismic survey alters blue whale acoustic communication. Biology Letters, 6(1), 51–54. https://doi.org/10.1098/rsbl.2009.0651

Gilbert, P., Walsh, C., Traut, M., Kesieme, U., Pazouki, K., & Murphy, A. (2018). Assessment of full life-cycle air emissions of alternative shipping fuels. Journal of Cleaner Production, 172, 855–866. https://doi.org/10.1016/j.jclepro.2017.10.165

International Maritime Organisation (IMO). (2014). Guidelines for the reduction of underwater noise from commercial shipping to address adverse impacts on marine life. https://wwwcdn.imo.org/localresources/en/MediaCentre/HotTopics/Documents/833%20Guidance%20on%20reducing%20underwater%20noise%20from%20commercial%20shipping,.pdf

Kaplan, M. B., & Solomon, S. (2016). A coming boom in commercial shipping? The potential for rapid growth of noise from commercial ships by 2030. Marine Policy, 73, 119–121. https://doi.org/10.1016/j.marpol.2016.07.024

McCauley, R. D., Day, R. D., Swadling, K. M., Fitzgibbon, Q. P., Watson, R. A., & Semmens, J. M. (2017). Widely used marine seismic survey air gun operations negatively impact zooplankton. Nature Ecology & Evolution, 1(7), 0195. https://doi.org/10.1038/s41559-017-0195

Merchant, N. D. (2019). Underwater noise abatement: Economic factors and policy options. Environmental Science & Policy, 92, 116–123. https://doi.org/10.1016/j.envsci.2018.11.014

Portvancouver. (n.d.). Ecoaction program. https://www.portvancouver.com/environmental-protection-at-the-port-of-vancouver/climate-action-at-the-port-of-vancouver/ecoaction-program/

Smith, T. A., & Rigby, J. (2022). Underwater radiated noise from marine vessels: A review of noise reduction methods and technology. Ocean Engineering, 266, 112863. https://doi.org/10.1016/j.oceaneng.2022.112863

Williams, R., Wright, A. J., Ashe, E., Blight, L. K., Bruintjes, R., Canessa, R., Clark, C. W., Cullis-Suzuki, S., Dakin, D. T., Erbe, C., Hammond, P. S., Merchant, N. D., O’Hara, P. D., Purser, J., Radford, A. N., Simpson, S. D., Thomas, L., & Wale, M. A. (2015). Impacts of anthropogenic noise on marine life: Publication patterns, new discoveries, and future directions in research and management. Ocean & Coastal Management, 115, 17–24. https://doi.org/10.1016/j.ocecoaman.2015.05.021