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A revolutionary propeller hub vortex cavitation-eliminating boss cap has successfully completed validation tests at a hydrodynamic research centre in Sweden and will now undergo ship model basin trials to verify the efficiency gains on larger commercial and naval vessels.
Initial computational fluid dynamics (CFD) tests based on a typical twin-screw vessel with V-brackets and a 90 m coastal general cargo ship showed that the Eco Boss Cap increases propulsion efficiency by up to 5%, compared to conventional propeller boss caps. Tests also assessed the device against more advanced energy-efficient boss caps currently in operation, and found it to be at least 3% more efficient.
“Overall, compared to the propeller boss caps currently available, the Eco Boss Cap 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 1–3 dB,” explained Dr Batuhan Aktas.
“The Eco 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, the Eco Boss Cap represents a significant advantage with a return on investment of less than six months,” he said.
How it works
The holes channelled into the Eco Boss Cap 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.
“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.”
The Eco Boss Cap is reportedly less expensive than conventional propeller hub cap fins that incorporate small blades or fins to hydrodynamically deflect the water flow, as it 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.”