You can’t compare total force output to efficiency like that. You need power in and power out.

_However, the global economic crash caused a decrease in consumer buying confidence. In addition to this, Marine Diesel Oil (MDO) and the related engine technology required to use it became readily and cheaply available. Fuel prices at that point meant that any savings achieved by the rotor were too small for shipping companies to consider the investment due to the lengthy payback period. _

So yeah cheap fossil fuels strike again

The exact quote is

“the propulsion force generated was less than the motor would have generated if it had been connected to a standard marine propeller.”

Based on that, the input power is a constant because they are comparing against the same motor. I would assume the power consumption is constant rather than bursty for either propulsion system, so there isn’t any peak-vs-avg power to be concerned about either.

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.