Hubless rim-driven thrusters more efficient
An electric hubless propeller whose blades are driven by an outer rim has many advantages over a conventional propeller. It is more efficient, quieter and does not risk damage caused by long fibers (floating fishing nets or ropes) clogged on the hub. According to a new report from Lighthouse and the Swedish Transport Administration, it is therefore ideally suited for maritime rescue and inland shipping.
The performance of a conventional marine propeller is greatly affected by the transmission of power through the hub and gearbox. It generates heat, for example, explains Hua-Dong Yau, researcher at Chalmers and author of the preliminary study Pilot Study of Electric Hubless Rim-Driven Thrusters for Transport in Inland Waterways.
“Since the rim driving an electric hubless propeller is cooled directly by the water, the motor is kept cool, making it more efficient. A conventional engine and propeller, which are much larger and heavier, also create significantly more vibration and noise. In addition, it risks getting tangled and stuck in cloudy waters with a lot of seaweed beds. In such waters, a hubless propeller is more suitable.”
The previous research on electric hubless rim-driven thrusters (RDT) has mainly been done in China, but no one has previously studied how the hydrodynamic efficiency of the propellers can be improved. And that is exactly what Hua-Dong Yau has done.
Between the driving rim and the propeller there is a small gap. If the geometric parameters of this were changed, Hua-Dong Yau's theory was that the hydrodynamic efficiency could be improved. And it turned out to be true. He found that the hydrodynamic efficiency was increased as the gap axial passage length was shortened, which was realized by increasing the oblique angle but fixing the gap inlet and outlet positions. Moving the inlet and outlet to further downstream and upstream positions had negligible effects on the hydrodynamic efficiency and led to recirculating flow within the gap near its inlet.
“It increases efficiency by approximately 5 percent”, said Hua-Dong Yau.
The pre-study Electric Hubless Rim-Driven Thrusters for Transport in Inland Waterways has been authored by Hua-Dong Yao (Chalmers).
In collaboration with: Alex Shiri (RISE), Fredrik Falkman (Swedish Sea Rescue Society), Fredrik von Elern (Swedish Maritime Technology Forum) and Magnus Karlsson (Kongsberg Maritime).