Increasing interest in underwater radiated noise from shipping
A recent article in the magazine Marine Propulsion & Auxiliary Machinery highlights the growing concern about environmental impact of ship noise emissions. Organisations such as IMO (MEPC), United States’ National Oceanic and Atmospheric Administration (NOAA) and EU (MFSD) are addressing the problem. This has lately been brought to wider public attention through articles published by national newspapers, e.g. The Guardian in the UK and The New York Times in the US. Marine Propulsion & Auxiliary Machinery highlights SSPA as an example of companies that offer services to help maximise both energy and environmental efficiency: “In addition to offering services such as ship design and hydrodynamics, safety and risk management and alternative fuels, the company offers a portfolio of energy efficiency and environmental tools and services relating to underwater radiated noise.”
SSPA offers predictive tools and noise reduction methods to assist clients who want to achieve greener shipping. As for naval vessels, the noise aspect now also needs to be considered at the initial design stage of commercial ships. A well-designed hull form will require less power and provide more uniform inflow to propellers, thus increasing the propulsive efficiency and reducing the underwater radiated noise caused by the uneven wake flow.
The propeller design point should be carefully selected to match the optimal efficiency with the most frequently operated speed/draft condition(s). For commercial ships it is hard to avoid cavitation for efficiency reasons, but cavitation can be controlled and kept to moderate levels.
All these measures imply an increased design effort, but the result is a quieter ship with higher efficiency and lower emissions. Regardless of the technology used for noise reduction, it is essential to assess the effectiveness of the noise reduction using model-scale measurements, CFD analysis or full-scale measurements.
Read more about SSPAs research on "Shipping and underwater radiated noise"
Read the full article in Marine Propulsion & Auxiliary Machinery
“Concerns grow about environmental impact of ship noise emissions”
Illustration: Frequency relationships between marine animal sounds and sounds from shipping. Figure courtesy of B. Southall, NMFS/NOAA.