The Trochoidal Concept
Underwater radiated noise isn’t just produced by large container ships, it’s also produced smaller boats and ferries. One way we can reduce the harmful impacts of underwater radiated noise is by designing quieter propellers. In France, our partners at Naval Group and its subsidiary SIREHNA have been testing an exciting new concept that might change the future of ship design.
The idea? Mounting a ship with vertical blades instead of the conventional propeller design found on most ships (which looks similar to a household fan). This ’trochoidal’ concept, as it’s known, was tested on a perfectly scaled-down model of a BC Ferry (crafted by Formes et Volumes) on Lake Guerledan in March 2023. The propeller was provided by ADV-Propulse.
As the model ferry was piloted around the lake, SATURN researchers measured the underwater radiated noise produced by the trochoidal system. The results of these acoustic tests are currently being analysed and we are looking forward to sharing them with you next year. In the meantime, take a look at the video below to see how the trochoidal system works and watch the tests on Lake Guerledan using the model BC ferry.
Risk to Marine Life
Naval Group has also assessed the risk to marine life from this system, and has concluded that the trochoidal propeller does not pose more risk for collision or entanglement than a conventional propeller. This is because the trochoidal propeller is placed in the same location as a conventional propeller, without projecting further below the keel line. In addition, the speed at which the trochoidal blades are spinning is much less than that of a conventional propeller, thus any physical contact would be with less force. Generally, the risks of this system are comparable to that of cycloidal propellers, which have been in use for many years.
Naval Group also notes the difference in flow between a conventional propeller and the trochoidal system. In the conventional design, the flow gathers a wider diameter of water as it converges toward the propeller. In the case of trochoidal propulsion, the flow is more linear, suggesting that there may be less risk of any object floating by to be sucked in. However, this is yet to be tested.
Numerical predictions are currently being undertaken for this model ship in order to improve the capability of propulsive providers to predict accurate hydroacoustic signatures before their production and uptake. We look forward to sharing the results of these tests when they are available!