Very curious, since there were commercialized versions reported back in 2019.
https://www.boatindustry.com/news/32122/sharrow-amazing-prop...
https://boattest.com/Sharrow-Propeller
And there are examples from online forums dating back to 2012:
https://www.boatindustry.com/news/32122/sharrow-amazing-prop...
https://boattest.com/Sharrow-Propeller
And there are examples from online forums dating back to 2012:
(1) Their patent application was filed on 11/6/2017. https://patents.google.com/patent/US10836466B2
(2) This propeller is different from those propellers, and the patent office found that the differences were patentably new and non-obvious.
Claim 1 is representative:
> 1. Toroidal propeller comprising: a hub supporting a plurality of elongate propeller elements in which a tip of a leading propeller element curves into contact with a trailing propeller element to form a closed structure with increased stiffness and reduced acoustic signature.
The element "in which a tip of a leading propeller element curves into contact with a trailing propeller element" seems to be common to all the independent claims of the patent.
https://www.overclock.net/threads/noiseblocker-nb-eloop-120m...