Steerprop draws on its extensive expertise in thruster design, hydrodynamics and ship integration to help vessels meet the most stringent low-noise notations.
Underwater Radiated Noise (URN) from ships—noise and vibrations from machinery and ship operations travelling through the water—can have a significant impact on aquatic life. As recognition of this impact has increased, reducing URN has become an important consideration for ship designers and operators, as well as port authorities and regulators.
Why reduce URN?
For operators there are two reasons to focus on reducing URN:
- Mission-specific requirements for certain applications that rely on minimal disruption to the marine habitat, such as marine research in sensitive areas, seismic studies for offshore infrastructure projects, and vessel engaged in aquaculture operations.
- Fulfilling requirements for port authorities (e.g., Vancouver Fraser Port Authority) and international vessel rating schemes (e.g., International Association of Pots and Harbors’ Environmental Ship Index, URN module) that can deliver incentives including reduced port dues.
Alongside IMO’s non-mandatory guidelines to support URN reduction efforts, there are several class notations validating that overall URN from ships has been assessed and verified as being below defined limits.
Steerprop’s propulsion design and integration optimisation has helped several vessels meet class, governmental and international requirements for URN.
How do propulsion solutions affect URN?
URN is measured holistically, with all noise from the vessel considered in one calculation. That means that noise from the engine, other machinery within the vessel and propellers contribute to URN.
The noise and vibrations resulting from propeller cavitation are amplified by the ship’s hull. This means that optimization for URN requires a holistic understanding of how both propeller design, and the propeller’s attachment to and interaction with the ship hull, will affect noise and vibrations.
Large, single propellers have a far greater impact on noise and vibration than thruster propellers due to higher loading, higher tip speed, obstructed inflow and disrupted wake distribution. However, thruster propellers still require careful design, positioning to and connection with the hull to minimize URN.
As with single-screw propellers in diesel configuration, there are parts of the drive configuration beyond the propeller that can affect URN. These include the motor, gears, bearings and shafting and how they are mounted and positioned.
How does Steerprop help minimize URN?
Steerprop can optimize thruster design and integration to help your vessel meet its project requirements. Due to the complexities of interactions with other elements of the ship design, this process is conducted on a project-by-project basis.
The drivetrain - comprising thruster motor, gearbox and shafting - contribute mechanical and electrical noise, which can be amplified by thruster housing. Areas that can be optimized include:
- Motor housing can be designed to reduce harmonic resonance and dampen specific frequencies.
- Gearing can be optimized to reduce mechanical noise by ensuring the most seamless meshing.
There are also many ways to reduce impact on URN from the propeller, beyond optimized design:
- Reduce loading through power management
- Reduce interaction with hull by optimally locating propellers
- Minimize potential for amplification of noise through flexible mounting
- For tunnel thrusters, optimize inlet design to reduce flow disturbances.
The world’s quietest icebreaking research vessel?
The new Polarstern is a cutting-edge polar and marine research ship being built for Germany’s Alfred Wegener Institute, to enter service in 2030. Destined for projects in highly sensitive marine environments in both the Arctic and Antarctic, it could be the quietest research vessel ever built, meeting strict acoustic requirements set by the International Council for the Exploration of the Sea—ICES 209.
Steerprop was initially contracted to supply main thrusters and hydrodynamic integration for the vessel, based on both its deep ice-class expertise and its efforts to optimise propulsion for URN. Following initial discussions, Steerprop’s scope was extended to include tunnel thruster design—making it the first supplier to take sole responsibility for propulsion and hydrodynamic integration on a Polar Class 2 icebreaker.
Read more in the press release
How is Steerprop advancing understanding of URN?
Steerprop has been involved in several research projects to both optimise its own propellers and to facilitate deeper knowledge of the complex factors influencing URN across all aspects of a vessel.
2015: Conducted simulations of URN performance of Steerprop CRP (contra-rotating propellers) installed on a RoPax ferry, with validation by DNV.
2016-2018: Participated in the Business Finland-backed research project SMULAN II/TP5 research project, developing a detailed mechanical thruster URN model based on simulations of the ferry configuration previously studied, calibrating the simulation model against measurement data. Z-drive and L-drive power transmission were compared for their URN response.
2021: Performed structure-borne noise and URN measurements for a RoPax ferry and an expedition cruise vessel, made together with Luode Oy--a company specializing in underwater measurements.
2021: Collaboration with Finland-based ATA Gears to study the impact of various motor and gear geometries and components on noise. Using FEM calculations, studied noise excitation and noise transmission mechanisms in our Z, L and LM units. Read the full article.
Speak to the experts
Contact Steerprop’s thruster design and hydrodynamic experts to learn more about how we can help optimise URN for your vessel—helping aquatic life thrive, earning valuable port incentives and fulfilling your mission requirements.
