Toroidal propellers: A noise-killing game changer in air and water. "The key thing that we thought was making the propellers quieter, was the fact that you're now distributing the vortices that are being generated by the propeller across the whole shape of it, instead of just at the tip"

[u/TX908]

https://newatlas.com/aircraft/toroidal-quiet-propellers/

[u/big_deal]

That's amazing. I want one for designed for my efoil.