Toroidal propeller

[5] The marine propeller was patented again in the late 1960s by Australian engineer David B. Sugden affiliated with Robbins Company of Seattle.

[7] The technology was adapted for fluid dynamics in the 2010s by Gregory Sharrow with twisted loops instead of traditional blades.

He patented propellers that addressed issues with rotary propulsion through the reduction of tip cavitation and vortices to increase performance in boats.

[8] Sharrow Marine argued that the benefits of lower fuel consumption, higher efficiency and reduced noise are even greater in water.

[11] Drone propellers made according to this principle have been shown to emit a frequency between 1 and 5 Hz, which is outside the audible spectrum for humans.