I think you can say theory, turned practice a long time ago.
The difference is? that many wouldn’t get the chance to build full scale. So the idea end up doing a loop. The old chestnut of where ideas go to die.
I wonder if they are good for energy production when anchored? I can’t say how many ships are out there like this? While my minds on? do you guys reckon? that the current three bladed turbines, could be retrofitted with a skin that does exactly this on the mast section?