Good article. Here’s the meat of it:
" The ship had proved inefficient on these voyages, with the power consumed by spinning 15m tall drums being greatly disproportionate to the propulsive effect when compared with conventional propellers. As the system could not compete economically, Flettner turned his attention to other projects and the rotors were removed."
This is saying you get less propulsion from the spinning sails than if you just put the same power into a regular propeller. If they worked well, you can bet Flettner would not have removed them from the ship.
And the section discussing “Saving 25%”, if you read carefully, is owned by a wind turbine company (Enercon) and they say “up to 25%” (compared to same-sized conventional freight vessels)"
That is two qualifiers to 25%. My guess is they are not counting the energy used to spin the cylinders, hence an illusion of “up to” 25%. Up to means “less than”, which could be only 5% or even zero or minus 5%!.
I’ll tell you what I think is going on here: In this climate of borderline insanity with people doing backflips to see who can appear to be the most politically-correct and carbon neutral, people are doing whatever it takes to have even the appearance of “making a difference”. It’s not the actual making of a difference that counts, since few people can figure out whether they actually ARE making a difference, but the emotion-based illusion of making this “difference”.
If faced with the facts, the politically-correct rationale is typically “Well, we’re raising awareness”. So, as we often see, even projects that end up using MORE fossil fuels are lauded and worshipped, as long as they look like they might use slightly less fuel. And after spending all that money to create this illusion, the companies know better than to tell people it doesn’t really save any fuel. They just pull out a figure indicting some minor savings and then quickly change the subject. It’s more about illusion, emotion, and public relations than anything else.
Did you know people have built a wind turbine using flettner rotors as blades? Yup, they apparently must have sucked too. Not that sucking is a bad thing for an airfoil,since that is how they work, but, well, you know what I mean.