A propeller hub vortex cavitation-eliminating boss cap, developed by EcoMarine Innovations, 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 vessels.
Initial CFD tests based a typical twin-screw vessel with V-brackets and a 90m coastal general cargo ship showed that EcoMarine Innovations’ Holy Boss Cap (HBC) – named thus to indicate the holes bored into the conically shaped hub – increases propulsion efficiency by up to 5%, compared to conventional propeller boss caps. The tests assessed the patent-pending HBC against more advanced energy efficient boss caps currently in operation, and found they are at least 3% more efficient.
EcoMarine Innovations is a ship research and development group at the University of Strathclyde, Glasgow.
Dr Batuhan Aktas, CEO EcoMarine Innovations said: “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. 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.”
Essentially, the holes channelled into the HBC 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.
EcoMarine Innovations CTO Ahmet Gurkan 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. 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.”
The HBC is reportedly less expensive than propeller hub cap fins that incorporate small blades or fins to hydrodynamically deflect the water flow, as HBC is easier to cast and requires less material.
Gurkan continued: “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. 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 says it is now looking for partners to help take the product to market.
Image: HBC prototype trials (source: EcoMarine Innovations)
