Sharrow tested quiet drone blades in water and found tipless propellers cut cavitation

A March 2024 Fast Company article credits Greg Sharrow, founder of Sharrow Engineering and Sharrow Marine, with inventing the original Sharrow propeller in 2012. After studying at Berklee College of Music, he worked in music production and wanted an ultra-quiet drone for live performances. Drone blades are loud because of cavitation, which also makes boat propellers noisy.

Sharrow knew blade tips are one source of cavitation and began reducing, and finally eliminating, the tips through iterative design. Because water is denser than air, he could build much smaller prototypes and found it faster and cheaper to test them in water than in the air.

That detour produced the surprise: the tipless folding propeller designs drastically reduced cavitation. The Sharrow CX, described in the article, has six blades in two triads that connect back to the shaft in a smooth twisted surface, a counter-rotating propeller the article calls the biggest propeller innovation since the 19th century.

Blade tips are a source of the low-pressure bubbles that cause cavitation.

Joining the blades back to the hub removes the free tip.

Water is dense, so small prototypes tested faster and cheaper there than in air.

He tested for cost reasons, so the marine effect surfaced almost by accident.

Testing in a cheaper medium can reveal that a fix built for one problem solves a bigger one elsewhere.

The article presents the CX as a sculptural, high-efficiency counter-rotating propeller. The excerpt gives no sales or independent test figures; the efficiency and noise claims are the article's own framing.