yes, that’s why i was surprised
you say an open screw is faster?
Assuming the same power input and equivalent levels of development/manufacture, yes. At higher RPM an open screw is more power efficient than a pumpjet as there’s a sort of “stall” effect in flow at the area between the blade tips and the shroud. It’s why you don’t see the airborne version of the concept on anything bigger than a small drone.
It’s worth noting that as commercial computer fluid flow modeling has gotten better and more accessible, there’s also been a huge demand to make quieter props/screws/fans from an area that isn’t so traditional.
Turns out that as electronics have proliferated, people have gotten more and more annoyed by cooling fan noise. Billions of dollars have gone into designing fans that are as close to silent as possible while still moving huge amounts of air. The experience and science behind that is readily available and can directly contribute to quieter in-water screws.
Here’s one example of a silent cooling fan, readily available on the market. Obviously moving air is a little different than moving water, but note the details of the fan - I selected a translucent unit so you could better see the blades. The strakes are not there for style.
https://www.amazon.com/Cougar-CFD12HBG-120mm-Cooling-Green/dp/B00DP5ZCS2?th=1