Everything Old is new again - Flettner Rotor Ship is launched

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

  1. rwatson
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    rwatson Senior Member

    Found a 16 foot catamaran version today

     
    Clarkey and hoytedow like this.
  2. rwatson
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    rwatson Senior Member

  3. DogCavalry
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    DogCavalry Senior Member

    Problem with Flettner rotors is they have have super high lift, for the projected area, but als high drag. L/D ratio is not suitable for a cat, except as a research platform.
     
  4. rwatson
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    rwatson Senior Member

    I'm not sure where you get that idea from. Do you have any examples to show what you mean ?
     
  5. DogCavalry
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    DogCavalry Senior Member

    Marchaj, Aerohydrodynamics of Sailing
     
  6. rwatson
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    rwatson Senior Member

    Edited:
    Hmm. I downloaded the book No obvious comment on multihulls found.
    It does re-iterates many of the same formulae and documentation already posted in this thread.
     
    Last edited: Mar 30, 2022
  7. rwatson
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    rwatson Senior Member

    "Marchaj, Aerohydrodynamics of Sailing"
    Interesting excerpt
    Marchi_Excerpt.png
     
  8. DogCavalry
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    DogCavalry Senior Member

    Most excellent. I have it in hardcover, bought back in '90. He provides some excellent polar graphs as I recall. Extremely high lift, much higher than most rigs, but also highish drag. And with multi hulls, L/D ratio is paramount. I've always thought rotors would be fantastic on a heavy round chinese junk, or similar hull. It's not like a boat like that is going to be sailing so fast that apparent wind is a problem. Brute power is what you want for those guys.
     
    Last edited: Mar 30, 2022
  9. DogCavalry
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    DogCavalry Senior Member

    Read his brilliant stuff on multihulls elsewhere in the book. It's about the worst edited book I've ever feverishly read and reread. Just dismall structure and organization. But fantastic all the same.
     
  10. zstine
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    zstine Senior Member

    Agreed: In the research paper below, spin ratio, aspect ratio and end disk size were varied and evaluated for L/D using a CFD model. The MAX L/D was 5.5 with SR=2, AR=8, de/d=3. A modern sloop rig typically has a L/D of 8 to 10 and wing masts can get L/D up in the 20's. So, a Flettner rotor is not appropriate for any high performance, speed wise, vessel, assuming you want to go upwind.. you'd tack through 140 degrees! haha However, they may perform well at angles below a beam reach.
    https://downloads.hindawi.com/journals/ijrm/2016/3458750.pdf
     
  11. zstine
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    zstine Senior Member

    I wonder if anyone has researched elliptical Flettner rotors? The end plate blocks tip vortex, but adds drag. Generally elliptical wings are the most efficient plan form as it reduces tip loss. Wondering if that carries over to Flettner rotors, especially in submerged applications like quantum stabilizers?
     
  12. rwatson
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    rwatson Senior Member

    I looked up the Morriseu paper,
    The Polars that he quotes ( D. R. Pearson, “The use of flettner rotors in efficient ship design,” are based purely on computer modelling) , and don't agree with actual experimental data from Thom OR NACA Technical Note 209, "Tests on rotating cylinders" by Elliott G Reid, Langley Memorial Aeronautical Laboratory. which is the basis for Jeremy Harris Excel workbook.

    ThomPolars.jpg

    This Data was purely derived from computer modelling.
    "The FR model was developed to be used in conjunction with Ptool, BMT’s proprietary marine power and propulsion tool [7]. "
    PtoolPolars.png
    Which show a suspiciously Low Upwind ability.

    Actual real-world Reports on Rotors Upwind performance are invariably very positive.

    I have also been perusing Jospeh Norwoods publication, and his comments on high performance multihulls.

    HighPerformance.jpg

    In the biggest configuration postulated, he calculates up to 40 knots performance. This is not low performance.
     

    Attached Files:

  13. rwatson
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    rwatson Senior Member

    I am attaching another page from Joseph Norwood's publication, 21st Century Multihulls, for future reference
    AYRS120P87.jpg

    Its significance is in 2 parts
    1) A formulae for calculating the power required to rotate Flettner Rotors
    2) A comment on an error that Thom made in his power calculations.

    These should be of real use to anyone contemplating further experimentation.
     
  14. rwatson
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    rwatson Senior Member

    A good introductory video
     

  15. Dolfiman
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    Dolfiman Senior Member

    You can also remind here that we already discussed the coherence of the Norwood approach in a previous thread where I finally proposed a rewriting formula with coefficients that can be directly used and compared with test results if any (attached documents of the quote # 35) :
    Flettner Rotors - Calculating Rotating Skin Friction | Page 3 | Boat Design Net
     
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