

That “source” is some NASA tutorial that just states that quote without any elaboration at the bottom. I don’t know how that passes as a source at all nor is it generally applicable in modern ships.
On the other hand there are multiple ships currently using these as additional propulsion system (as you can see further below in the wiki article). Flettners inital prototype used rotors as exclusive propulsion system. One could also use a kite or a sail by using the wind in favourable conditions.



An infestation of the pine shoot moth produces a very similar structure. The eggs are laid into the shoot killing it. The pine reacts by producing a new shoot on the side which curles towards the vertical again producing these characteristic bends in pines.
See here for a very early stage: