Everything Old is new again - Flettner Rotor Ship is launched

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

  1. tspeer
    Joined: Feb 2002
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    tspeer Senior Member

    At first I was confused by Figure 13 because it appeared that the rotor was producing thrust directly into the wind. But Figure 10 indicated the drag coefficient was always greater than approximately 1. Then I noticed that the origin of the polar plot was not zero thrust, but -150 kN! This is highly misleading.

    I question his conclusion, "Regarding the capability of FR to act as a propulsion device, it is confirmed that, in terms of magnitude, CL, and aerodynamic efficiency of FR is much higher than the values given by a wing of comparable aspect ratio." It's true that the lift coefficient is much higher than for a wing, but that really means the rotor is a more compact means of producing lift since the wing chord can be increased to produce the same lift with the same span. The efficiency, however, is not higher than what can be obtained with a wing. Figure 10 shows a maximum lift/drag ratio of 5.6 for the aspect ratio=8 rotor with large end plate - the best case. An L/D of 5 - 6 is on the order of what one would expect for the total aerodynamic lift/drag ratio of an entire sailboat, including the windage of the hulls, crew, rigging, nets, etc. The lift/drag ratio of the wing alone is several times better.

    And that doesn't include the power that is supplied to spin the rotor. If the power required to turn the rotor were applied to normal screw propulsion in addition to thrust from the wingsail, the wingsail is far more efficient than the Flettner rotor. The wingsail also wins out if the power is applied to boundary layer control instead of direct propulsion.

    I believe the case for the Flettner rotor is not aerodynamic, but in the area of handling and integration with the rest of the ship. The diameter of a Flettner rotor is smaller than the chord of a wingsail that can produce the same lift. This means it can fit between cargo holds without interfering with loading and unloading of the ship. The lift from a Flettner rotor can be easily regulated by varying the rotation rate. This makes it straightforward to effectively feather the rotor in high winds. However, the high drag of the rotor cannot be reduced, and a feathered wingsail has a fraction of the drag of a stopped rotor. So the heeling moment from the rotor in a beam wind can put a limit on the size of the rotor.
    Manfred.pech and CocoonCruisers like this.
  2. Squidly-Diddly
    Joined: Sep 2007
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    Squidly-Diddly Senior Member

    someone needs to come up with good spiral etc effect.
  3. rwatson
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    rwatson Senior Member

    You are going to have to show the Math for that assumption.

    Yeah, but what fraction ?

    In 1930's, Rotors had less drag than sailing sailing ships with bare masts and rigging.

    I found a spreadsheet to calculate static loads on rotors, that I will upload for future reference.
    It has a section I am working on to calculate Drag on Airfoils. It shows about half a tonne of drag in gale force winds for a 7 metre x 3 metre Rotor, not huge.

    Also, Wing Sails have to constantly feather into adverse winds, putting lots of strain on the structure, and the ship too if the supporting column has stays..
    It's no wonder they havent been used for commercial installations.

    And the BIG benefit of Rotors is that they dont require constant attitude adjustment for optimum power, being omni-directional. In fact, at their optimum ~ 100 degrees wind angle, there is very little heeling moment.

    Attached Files:

  4. 1J1
    Joined: Sep 2012
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    1J1 Senior Member

    They are returning recently:

    DSIC and China Merchants test landmark sail propulsion system on VLCC - https://splash247.com/dsic-and-china-merchants-test-landmark-sail-propulsion-system-on-vlcc/ - retractable wing sails.

    Econowind solution - 2 retractable wing sails stored in a container.
    Econowind | Econology by wind https://www.econowind.nl/
    rwatson likes this.
  5. rwatson
    Joined: Aug 2007
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    Location: Tasmania,Australia

    rwatson Senior Member

    "2 retractable wing sails stored in a container."

    Seems a pointless exercise. Can you imagine two A class catamarans towing that thing.
    That's all they are equivalent to.

  6. Dolfiman
    Joined: Aug 2017
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    Dolfiman Senior Member

    Another project, "Zéphyr et Borée" , a cargo ship with wing sails and LNG based propulsion, by students with the support of VPLP which try to develop a wing sail for various type of maxi ships. If interested, you can vote for them before June 3 (you have first to register to "The Aviva Factory", a Foundation of Aviva Insurance Company) , and if they are part of the 40 selected projects , they will receive a price :
    "Zéphyr et Borée" : #LaFabriqueAviva : découvrez Zéphyr et Borée qui participe à @LaFabriqueAviva #RSE #Concours #Votes https://lafabriqueaviva.fr/fr/project/2831/show#
    The Aviva Factory : La Fabrique Aviva - Donnez vie à vos Projets entrepreneuriaux https://lafabriqueaviva.fr/fr/
    VPLP wing yacht concept : Projects - VPLP Design https://vplp.fr/realisation/evidence/58.html

    Dolfiman, 2 minutes ago Edit Delete Report
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