Key Takeaways from the Latest LOWNOISER Webinar
The LOWNOISER project recently hosted a webinar exploring how analytical modelling can support the development and validation of underwater radiated noise (URN) reduction measures for ships. The webinar brought together experts from industry and research organisations to present how predictive modelling is being applied to four real vessel demonstrations, covering propulsion systems, air lubrication technologies, operational measures and machinery vibration reduction.
The webinar marked an important step in the project’s transition from prediction and design towards full-scale demonstration and validation. Rather than developing models solely to explain observations after testing, the project is using analytical approaches to predict the effectiveness of mitigation measures before they are installed on vessels, helping guide investment and design decisions.
From Prediction to Implementation
As introduced by Emilie Dorgeville from Maritime CleanTech, the LOWNOISER project aims to move from prediction to implementation by combining four key stages:
- Development and prediction of noise reduction solutions
- Demonstration and validation under real operating conditions
- Assessment of technical and environmental impacts
- Translation of results into guidance for industry, regulators and future standards
The webinar focused specifically on the role analytical modelling plays in this process and how models are being used to assess expected noise reductions before full-scale testing takes place.
A central element of the work is the use of the Piano model, a physics-based analytical tool that predicts ship noise from propeller cavitation, engines and auxiliary machinery. Throughout the project, this model has been expanded and adapted to address technologies and noise sources that were not originally represented, including bevel gear noise, engine mounting systems and air lubrication systems.
Case Study 1: Quieter Gears for Havila Capella
The first demonstration focuses on Havila Capella, a passenger vessel operating along the Norwegian coast. The objective is to reduce underwater noise at the source through optimisation of the bevel gears installed in the vessel’s azimuth thrusters.
Presented by Andre Böhme from Kongsberg Maritime, the work demonstrated how analytical models were used to optimise gear micro-geometry in order to reduce force excitations generated during gear meshing. Rather than redesigning the overall gear configuration, the team focused on subtle modifications to the tooth geometry, targeting the vessel’s most common operating condition.
The modelling indicated significant reductions in gear excitation forces, particularly at the dominant first gear mesh frequency. Baseline measurements have already been completed and new gears are due to be installed during an upcoming dry-docking period. Follow-up measurements will be used to compare the predicted reductions with real-world performance.
This work attracted particular interest during the discussion session, as azimuth thrusters have traditionally been considered challenging from an underwater noise perspective. The project is demonstrating that targeted gear optimisation may provide a practical pathway to quieter propulsion systems.
Case Study 2: Air Lubrication Systems and Underwater Noise
The second demonstration investigates whether air lubrication systems (ALS) can contribute to underwater noise reduction in addition to their established role in improving vessel energy efficiency.
As explained by Luca Savio from SINTEF Ocean, two potential mechanisms are being investigated:
- Reduced propulsion power requirements resulting from lower hull resistance.
- The potential for the bubble layer beneath the hull to modify how sound is transmitted from the vessel into the water.
While power reduction effects can be modelled using existing methods, the acoustic behaviour of air lubrication systems is more complex. The project has therefore developed new modelling approaches to investigate how bubble size, bubble concentration and air-layer characteristics influence sound transmission, reflection and absorption.
One important conclusion from the presentation was that air lubrication does not automatically result in reduced underwater noise. The acoustic performance depends strongly on the operating conditions and characteristics of the bubble layer. The project has shown that these factors can be analysed and incorporated into predictive models, providing a basis for future optimisation.
Future work will seek to better understand additional factors such as compressor-generated noise and air-flow effects within the system.
Case Study 3: Operational Measures and Real-Time Noise Monitoring
The third demonstration explores how vessel operations, particularly speed, influence underwater noise emissions. Numerous studies have shown that reducing speed can lower underwater radiated noise, but crews currently have limited access to information about the acoustic impact of operational decisions.
To address this, the project is combining analytical predictions with onboard monitoring systems. These systems include vibration sensors in the machinery room and on the hull, cavitation monitoring equipment comprising accelerometers and pressure measurements near the propulsion system. By combining measured data with modelling outputs, the project aims to provide more accurate estimates of vessel noise emissions in real time.
Presented by Roque Andres of TSI, the work demonstrated how this hybrid approach can improve agreement with measured vessel noise signatures compared with analytical modelling alone. The long-term objective is to provide ship operators with information that can support operational decisions in environmentally sensitive areas.
Case Study 4: Engine Mount Optimisation
The fourth demonstration focuses on machinery-related noise and the role of engine mounting systems in transmitting vibration into the ship structure. The case study is being conducted on the expedition vessel Fridtjof Nansen, operated by HX Expeditions.
Jørgen Løtvedt from Bergen Engines explained how the team extended existing modelling approaches to better represent the frequency-dependent behaviour of engine mounting systems. Current analytical models typically assume a fixed reduction factor for mounted machinery, but the project found that mounting design can significantly influence vibration isolation performance.
The proposed upgrade involves replacing existing mounts with softer isolation systems designed to reduce the transmission of engine vibrations into the hull structure. Modelling predicts a 3 to 4.5 dB reduction in machinery-related noise at key frequencies. Measurement campaigns are already underway and will continue after installation of the new mounting system to verify these predictions.
Importantly, the solution relies on commercially available technologies, which means the findings could have practical relevance for a broad range of vessels.
Industry Perspectives and Discussion
The webinar concluded with an active discussion involving shipowners, shipyards, technology suppliers, researchers and regulators. Participants expressed particular interest in gear optimisation, onboard noise monitoring and engine mount upgrades, while also highlighting the importance of full-scale validation before widespread adoption.
Several contributors noted that predictive tools such as the Piano model can play an important role during the design process, provided that sufficient measurement data are available to validate their accuracy. The discussion also highlighted growing interest from ports and maritime administrations in underwater noise reduction initiatives and monitoring activities.
Looking Ahead
A recurring message throughout the webinar was that analytical modelling should be viewed as a decision-support tool rather than an end in itself. The true value of these approaches will be demonstrated through the ongoing full-scale trials taking place across the four LOWNOISER demonstrators.
As the project moves further into its demonstration phase, future webinars will present validation results and explore additional topics, including the biological impacts of underwater noise and the project’s work on marine life. The recording of this webinar is available for anyone wishing to dive deeper into the technical presentations and discussions.
Watch the webinar recording to learn more about the analytical methods, modelling developments and demonstration activities supporting quieter and more environmentally sustainable shipping.