Everything Old is new again - Flettner Rotor Ship is launched

Discussion in 'Boat Design' started by rwatson, Sep 1, 2008.

  1. Clarkey
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    Clarkey Junior Member

    Here is a photo of a rotor sail in a race:

    Interesting to see the relative pointing angles.
  2. apex1

    apex1 Guest

    You are really a pretty bad example of a well established bias!
  3. Milan
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    Milan Senior Member

    Cousteau’s, (actually team of engineers led by L. Malavard and B. Charrier), solution was different then Flettner’s. They designed “turbo sail” – hollow cylinder with movable wing-shaped shutter and fans that suck air from the cylinder creating lower pressure on one side. That under-pressure accelerate air flow on one side of the cylinder…

    System was tested full size in 1983, with the catamaran Moulin à Vent with one “turbo sail”, during Atlantic crossing.

    After that Alcyone was built. She sailed a lot, Cousteau’s team claim fuel savings of about 35% compared with motor ship on long passages.

    There are few short films on the net that give general idea how it works. It was explained and shown well in one or two of Cousteau’s documentaries from the eighties.

  4. EuroCanal
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    EuroCanal Junior Member

    There's a "Foil Simulator" web-page here:http://www.grc.nasa.gov/WWW/K-12/airplane/foil3.html which will calculate the lift generated by a rotating cylinder. It looks like they work best in strong winds. In light breezes, the cylinder 'stalls' at a low rotational speed, so is limited in the amount of lift it can generate. The lift generated per unit length is roughly:

    pi^2 . d^2 . s . V . rho

    d = diameter, s = rotational speed, V = wind speed, rho = gas density.

    (First order solution for an ideal flow). However the stall speed, S is proportional to V / d, so maximum lift is proportional to :

    d . V^2

    - double the wind speed to get 4 x the lift.
  5. DougCim
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    DougCim Junior Member

    I gave up looking for comparative information on boats.
    It seems like every person who ever bothered to think a Flettner rotor boat was a good idea, didn't bother to also obtain a regular sailboat to compare the results against.


    What is a LOT easier to compare, is wind power-generation turbines.

    I started out tracking down the cover article of this example-
    which is on Google books-
    ...He got a $48K grant from the DOE to build it, but couldn't complete it. The GENERATOR it was supposed to run, he just couldn't afford. And unfortunately for science, that was the best way to determine how efficient it really was. But he was really, really sure that it was making like, way lots of power:
    "...The major thing I don't have is the horsepower-versus-wind-speed curve", he laments. "And that's what will prove whether or not a Magnus effect turbine is economical. " (p. 62)​

    Apparently it wasn't.
    The PopSci article noted that SoCal Edison was interested, but web searches 27 years after this story appeared don't turn up any Magnus-rotor windmills ever built or operated by them.

    The PopSci article has a cutaway view of the hub internals; I'm not even sure what all's going on in there. The diagram text says that the rotors are only spun with external power to start them spinning, and then the motor can be shut off as it's not necessary.
    This looks like a perpetual-motion machine to me. If a electric motor is used to (1) spin five tubes to create a Magnus effect, and then (2) those five tubes spin around a windmill hub, there will always be losses between the two stages (1) and (2), so you'll never get more power out than the electric motor puts in.

    Also I've not found any other articles that claimed the Magnus-tube-spinning motor could be turned off, or that the rotating of the individual cylinders could otherwise be powered by the wind. Have any of you?


    Most of the actual, real-metal work of Magnus wind turbines has been done by a lone Japanese company named Mecaro:
    I found a number of research projects, but could not find any other company actually selling a product.

    They moved to a design using spiral fins around the cylinders.
    On the above linked page they note that-
    "... Since then, many countries have tried to develop the cylinder-blade windmill, but have not been successful to put into practical use. There was a problem to overcome that the smooth surface of the cylinders required top speed spinning of the cylinders, which consumed more power than the wind turbine could generate. ..."​

    The Mecaro website has a webcam page, by the by. When I looked, the windmill wasn't spinning. :p
    But at least it is a real windmill, that they really built.
    There's another (nameless) company that all they seem to have produced so far is generic-looking CGI movies of imaginary silvery spiral-Magnus windmills that work perfectly.

    So okay, Mecaro has their spiral thing going on.
    Nobody else seems to be doing it that way, but anyhow.
    How many have they sold? .....Well, they don't say how many are sold or installed. The few photos I find on the company website or elsewhere are all located in or around the town in which the factory is located, leading me to believe that they are all "test installations" at least partially owned by the company itself.

    Well, maybe most people are dumb and just scared of new things, and don't recognize a technological breakthrough when they see it?
    Let's compare the specs of the Mecaro spiral-Magnus windmill with a similar-sized conventional (airfoil-blade) type:

    Mecaro spiral magnus 5-rotor windmill - (specs given on the bottom of this page)

    Wind Turbine Diameter........ 11.5m (37.7 feet)
    Rated Output.................... 12kW
    Rated Wind Speed.............. 11m/s

    And here's a "normal" windmill I picked randomly from Google- (I went looking for windmills that had rotors close to the same diameter as the Mecaro spiral-Magnus)

    Aeolos 20kw:
    Rotor Blade Diameter.......... 10.0 m (32.8ft)
    Rated Power....................... 20 kw
    Rated Wind Speed.............. 10 m/s (22.3 mph)

    How strange,,,,,, in ~10% less wind, the slightly-smaller-diameter conventional 3-blade windmill produces nearly twice the power that the spiral Magnus 5-blade does.

    Okay, maybe Aeolos are a bunch of lying crooks. Who cares what they say?

    Here's another model from another company, A & C Green Energy-

    Powermax 20K:
    Rotor Blade Diameter.......... 33 ft
    Rated Power....................... 20 kw
    Rated Wind Speed.............. 24 mph

    Another slightly-smaller 3-blade airfoil windmill, that produces nearly twice as much power in the same wind......

    Here's another example, from Hummer Wind Power-

    20kw (model)
    Blade Diameter............... 9m (29.5 ft)
    Rated Power................... 20kw
    Rated Wind Speed.......... 10m/s (22 mph)

    And again: slightly smaller rotor diameter, only three airfoil blades, and yet producing nearly twice the power.


    If you want a boat with a Flettner rotor, go ahead and have fun with it, you only go around once in life after all... but there's real reasons that most engineers ignore them, and it's not because they're too dumb to understand it, or nobody told them.
    Last edited: Aug 31, 2010
  6. rwatson
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    rwatson Senior Member

    Yes, that intrigues me too. Jo Norwood was very keen on many disks - and at one stage I had some formulae that purported to explain the reasoning. I will have to locate it again. My instinct is that the vortex controlling characteristics actually regain a lot of lost energy, though having multiple disks at an angle to the incoming airstream (when the boat heels) may also exhibit some energy gains. I would love to see a "smoke" test in an air tunnel.

    The question of power input versus power gained has been a contentious one over the years, but physics has resolved it in favour of the Flettner rotor.

    I suspect that the challenge isnt so much the speed of the boat, but a combination of managebility and power. In my bones I feel that the Rotor is more a candidate for high load, low skill controllabilty (especially with a computer to calculate optimum spin rates under different wind conditions) for commercial fossil fuel savings

    As Apex so umm...... diplomatically ...... pointed out, much of the literature I have submitted in this thread has been based on real world experience, starting from the conversion of the Buckeau, right through to the "Tracker" conversion.

    Once again, the figures are all there if you care to take the trouble to investigate. I guess the official definition of what it is probably pales against what it may possibly do.

    Keep up the good work with the "black hat", it keeps the enthusiasts honest :)
  7. DougCim
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    DougCim Junior Member

  8. rwatson
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    rwatson Senior Member

    Flettner Rotor and Windmills

    Not an apt comparison. Flettner himself did a lot of work investigating windmill applications, and found he could generate more power by putting blades on the end of Flettner rotors than from purely rotors alone. As you have found, the spinning rotor is fraught with gotchas.

    At the risk of repeating myself, by now there are lots of examples on this thread
  9. rwatson
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    rwatson Senior Member

    Love it! What a great experiment for inspiring the up and coming generations. Reminds me of the Australian Aboriginal "roarer", ( yes, like Crocodile Dundee used) when he spoke of the sound it can make.

    This technique was also considered as an alternate power source to a Flettner Rotor, as it spins itself without secondary power. It appears that the vibration induced in life size experiments killed the idea.

    In fact, I understand vibration that caused many problems in the original Flettner Cargo boats.
  10. rwatson
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    rwatson Senior Member

    Great inclusion to the thread, well done.

    And I agree with your summation - there are definitely particular uses for the Rotor - not an "all purpose" solution.
  11. apex1

    apex1 Guest

    It is so easy to contradict a system one does not understand. Leave it to convince us, convince you instead.
    Or give up your idiotic fight against a well proven system.

    You obviously don´t grasp the principle. Never mind. But then, don´t try to teach us your premature math´s!

    A motor drive?

  12. DennisRB
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    DennisRB Senior Member

    Hey Daniel. I have not taken it personally. Just trying to clarify that it IS a Flettner rotor boat and why. But you don't need to believe me. :)

    I have let Stephen, who owns the site and boat know about this thread. He said the tapered rotor is indeed an attempt to reduce lift toward the top therefore reducing tip vortex. I hope he joins in as I think he would know more than anyone here about flettner rotor boats, since he designed and built one and came up with his idea independently.

  13. DennisRB
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    DennisRB Senior Member

    How is it possible to drive a 11 foot dingy to hull speed with only 20w of power without extra power coming in from somewhere?

    Is it possible to create a 20w wind gen? Obviously, so if you hooked that to the 20w electric motor it would be 100% wind powered. But according to you "nobody can figure out" yet I just did it and I am no genius.
  14. DougCim
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    DougCim Junior Member

    The question I was attempting to convey here was: is the rotor's lift limited by the motor input power, or the prevailing wind, or both?

    My thoughts are that it is limited by the motor input power, since (one explanation of it somewhere I read claimed that) the cylinder's surface must be spun faster than the prevailing wind for the whole thing to work. And that is why I consider it to be a motor drive.

    The Flettner rotor concept as a means of propulsion appears to be the aerodynamic equivalent of an "overbalanced wheel".
    One cannot build a device that can-
    1) use a small amount of engine power to
    2) generate a quantity of lift, and then
    3) convert that lift back into a larger amount of engine power than you began with.

    It just doesn't work, at least in my universe.

  15. DennisRB
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    DennisRB Senior Member

    You fail at science.
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