Toroidal propellers: A effective noise reduction and gain in efficiency in air and water

Good news! It is not really new and still too expensive for now.

"... Sharrow Marine has been getting frankly spectacular results from boat propellers that use toroidal loops instead of standard blades. After several years of development, the company has now tested its props against hundreds of standard propellers, and the difference is incredible. Sharrow's props simply don't create tip vortices – a major source of energy loss and a surprisingly large component in the overall noise of an outboard engine. ...
The drawback here is price; they cost US$4,999 a pop regardless of which model, where a regular propeller might go for closer to US$500. ..."

The gain in efficiency is ridiculous in the water at midrange RPMs, filling in a pronounced hole in a boat's acceleration curve and conserving huge amounts of energy

Toroidal propellers: A noise-killing game changer in air and water These strangely-shaped twisted-toroid propellers look like a revolutionary (sorry) advance for the aviation and marine sectors. Radically quieter than traditional propellers in both air and water, they're also showing some huge efficiency gains.

Toroidal propellers: a radically quieter and more efficient design that can boost fuel economy by 20% when swapped onto a marine motor