Ship URN mitigation by air injection: model-scale experiments and application to full-scale measurement data

It is recognised that continuous underwater radiated noise (URN) from shipping needs to be mitigated in order to minimise impact on marine animals. To this end there are numerous technical and operational URN mitigation measures, although extensive data concerning their effectiveness is not always available in the open domain. Examples of this include the so-called ‘Masker’ and ‘Prairie’ systems, designed to reduce machinery and propeller cavitation noise respectively by means of air injection. These types of systems are being studied within the EU Horizon
2020-funded project SATURN.
In this paper, we report model-scale sound measurement tests of both systems and demonstrate application of the
measured data to a ship-scale test case. Two dedicated ship models were made based on a tanker hullform, with custom air injection systems developed. An overview of the model test campaign is reported, covering preparation, measurements and data analysis. After this, results of the full-scale application case are presented, including system power requirement estimation alongside URN abatement potential.
From the model tests URN reductions of up to about 22 dB and 12 dB were found for the Masker and Prairie-like systems respectively, although for the ship-scale application this is limited to about 10 dB at the vessel design speed.