VIDEO: New propeller boss cap promises major efficiency gains

It's called the Holy Boss Cap because it has holes in it. [Image: EcoMarine Innovations]

EcoMarine Innovations, a research group at the University of Strathclyde in Glasgow, Scotland, has developed a new propeller hub vortex cavitation-eliminating boss cap that promises major gains in propulsion efficiency.

Called the Holy Boss Cap, the conical shaped hub has holes (hence the name) bored into it that affect the high pressure in the hub vortex by redirecting the flow downstream. The resulting low-pressure swirl flows in the opposite direction to conventional hubs, behind the propeller blades, reducing propulsive drag, fuel consumption and maintenance costs.

Holy Boss Cap (above) eliminates propeller hub vortex cavitation by redirecting the water flow behind to increase propulsive efficiency by up to 5%. Conventional propeller hub vortex cavitation can be seen below.

The Holey Boss Cap has successfully completed validation tests at a hydrodynamic research center in Sweden and will now undergo ship model basin trials to verify the efficiency gains on larger commercial and naval vessels.

According to EcoMarine Innovations, initial computational fluid dynamic (CFD) tests based a typical twin-screw vessel with V-brackets and a 90-meter coastal general cargo ship showed that the Holy Boss Cap (HBC) increases propulsion efficiency by up to 5%, compared to conventional propeller boss caps.

Tests also assessed the patent-pending HBC against more advanced energy efficient boss caps currently in operation, and found the HBC at least 3% more efficient.

“Overall, compared to the propeller boss caps currently available, HBC improved propeller efficiency by 3.1% and thrust by 1.1%, while reducing torque by 2%, rudder cavitation by 10%, and propeller induced noise by 1-3dB,” said Dr. Batuhan Aktas, CEO of EcoMarine Innovations. “The Holy Boss Cap eliminates completely propeller hub vortex cavitation, the main source of rudder erosion, and reduces associated propeller efficiency losses, which can be as much as 8%”

“Considering the investment levels required for other energy saving devices currently in the market and the potential fuel savings, Holy Boss Cap is a game changer with and ROI of less than six months,” he added.

“With shipowners grappling with new environmental legislation and emissions reporting rules, zero propeller hub vortex cavitation can help towards ESG, EEXI and CII goals, improve efficiency and reduce the costs associated with cavitation induced rudder erosion,” said Ahmet Gurkan, chief technical officer at EcoMarine Innovations.

The Holy Boss Cap is reportedly less expensive than propeller hub cap fins, that incorporate small blades or fins to hydrodynamically deflect the water flow, as the Holy Boss Cap is easier to cast and requires less material.

“What we have designed is a propeller boss cap that is 5% more efficient and costs 50% less to manufacture than current conventional propeller hubs. Considering the minimal investment required, this is a significant level of saving,” Gurkan said.

“We are delighted that CFD trials have validated the concept and will now to take the development to the next stage and start secondary model tests in March,” Gurkhan continued. “We will scale up hole areas by 60% and expect to achieve improved performance by eliminating any negative scale up effects. We are also in advanced discussions with several shipowners that have expressed interest in installing HBC on their vessels as early adopters.”

EcoMarine Innovations is now looking for partners to help take the product to market.

More on the HBC HERE