Page 51: of Maritime Reporter Magazine (May 2024)

BOSS CAP

Holy Boss Cap undergoing trials losses. However, an early version of the innovative ‘holy’ the effects of variables such as chamber volume and pro? le, design failed to gain traction as it was not hydrodynamically number of holes, and angle of the holes. ef? cient, as the holes reduced the ef? ciency of the propeller. When we compared the HBC with more advanced energy-

The revised design of the HBC, which we implemented fol- ef? cient boss caps currently in operation, we found that it to lowing extensive studies in partnership with the University, be at least 3% more ef? cient. Overall, compared to standard addressed these problems with carefully placed and angled propeller boss caps, the HBC improved propeller ef? ciency by holes bored into a conically shaped hub. The holes channelled 3.1% and thrust by 1.1%, while reducing torque by 2%, rud- into the hub affect the high pressure in the hub vortex by redi- der cavitation by 10%, and propeller induced noise by 1-3dB. recting the ? ow downstream. The resulting low-pressure swirl We expect the HBC to be capable of delivering increases in ? ows in the opposite direction to conventional hubs, behind propulsion ef? ciency of up to 5%, compared to conventional the propeller blades, reducing propulsive drag, fuel consump- propeller boss caps.

tion and maintenance costs. These potential savings were further con? rmed by a Eu-

To assess the effectiveness of the new design, we carried ropean cavitation tunnel testing facility, where savings more out computational ? uid dynamic (CFD) tests on a typical than 2.1% were found despite challenging scale effects. twin-screw vessel with V-brackets and a 90m coastal general Given the pressing emissions-reduction challenges that the cargo ship. Using local workstations running parametric opti- shipping sector faces, we believe it is not enough to develop a mization software combined with CFD software, we studied solution without ensuring that it can be scaled in a meaning- www.marinelink.com 51

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