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...
https://www.marinelog.com/technology/video-new-propeller-boss-cap-promises-major-efficiency-gains/