Stand Up Paddleboard--on foils!

Discussion in 'Boat Design' started by Doug Lord, May 1, 2016.

  1. Doug Lord
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    Doug Lord Flight Ready

  2. Rurudyne
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    Rurudyne Senior Member

    Cool!

    Humorously: someone needs to make a foiling-sail-recliner with cup holder for your beer.
     
  3. Doug Lord
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    Doug Lord Flight Ready

    ===============
    I'm working on it for my caffeine-free diet coke!
     
  4. daiquiri
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    daiquiri Engineering and Design

    Great stuff, Doug. IMO, with a pair of good legs it might be even possible to go upwind for a short time.
    At claimed 20 mph, (9 m/s), that foil should require no more than 500-600W of average input power, which means 1000 W for each pumping stroke. It is a power output which can be produced by a well-trained person.
     
  5. Doug Lord
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    Doug Lord Flight Ready

    Slavi, I bet there would be many times that you could foil both directions parallel to almost any coast? Believe me: this is pretty near the last thing I expected to see in the Great Foiling Revolution!!
     
  6. daiquiri
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    daiquiri Engineering and Design

    IMO, a more efficient foil design would be necessary to achieve that. I came to 500W power output with few calcs of the foil geometry visible in the video and pics on the http://www.gofoil.com/ website.
    But 500 W of continuous average power is not for everyone, and cannot be sustained for long. This website: http://mapawatt.com/2009/07/19/bicycle-power-how-many-watts-can-you-produce claims (to be verified, I don't have time to do it) that the current 1-hour world record is 430 W of continuous average power output.
    The rest of us common mortals can only produce up to 200-250 W of power for an hour or so, if in good physical shape. Hence, what you say might be possible, but not with this foil design, IMO.
     
  7. Doug Lord
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    Doug Lord Flight Ready

    Slavi, in that whole video I only saw the guy use the paddle once? I don't know about your power required calculation. It seemed to me like very, very little power was required to sustain flight.
     
  8. daiquiri
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    daiquiri Engineering and Design

    I have reviewed the drag figures, and they might be more like 400 W. It comes from a simplified model of the foil made with the XFLR5, which gives approx. 400 W at 9 m/s, for a total weight of 90 kg.
    If it can be of interest for you, I have attached here the XFLR5 model of that thing.

    Regarding the question of where the power comes from - I have noticed that the guy is doing slight squatting (up/down) motion with his legs from time to time, occasionally helped by the paddle.
    So some of the power comes from this "pumping". Say that the power input from his body equals a comfortable value of 200 W.
    The rest of the power then must come from the wind. He is foiling downwind, and the choppy sea tells us that there was quite some wind during the videotaping.
    So, how much wind is required in order to receive 200 W of power? This is the calulation:
    - aerodynamic power formula: Paer = 0.5 rho V^3 A Cd
    - water speed: Vw = 20 mph = 8.9 m/s
    - average drag coefficient of a standing human body: Cd = 1.35
    - average frontal area of a standing human body: A = 0.65 m^2
    - required aerodynamic power: Preq = 200 W
    By equaling Paer and Preq, we get that an apparent air speed of Vapp=7.2 m/s coming at his back will provide the required 300 W.

    The true wind speed is the sum of the water speed and apparent wind speed:
    Vwind = Vw + Vapp = 8.9 + 7.2 = 16.1 m/s = 31 kts

    Considering the sea state in the video, it imo looks plausible.
     

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    Last edited: May 2, 2016
  9. David Cooper
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    David Cooper Senior Member

    You could fit a lot of battery into that board. Could an impeller be involved and not show up in the wake?
     
  10. daiquiri
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    daiquiri Engineering and Design

    I see where you are aiming. But the numbers from the previous post show that the thing can indeed work with the use of combined human and wind power, so it is not necessarily a fake. ;)
    Actually, considering that foil manufacturer (http://www.gofoil.com/) is using that video to publicise his product and the foiling capabilities of SUPs, I highly doubt it is a fake.
     
  11. Doug Lord
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    Doug Lord Flight Ready

    Flying SUP!

    No way its powered and/or a fake!
     
  12. daiquiri
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    daiquiri Engineering and Design

    Just noticed that I have used the word "videotaping" there... A particular which tells something about my age, I guess. ;)
     
  13. John Perry
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    John Perry Senior Member

    I was also amazed to see this for the first time. It looks to be wonderful fun. Regarding the question of where the power comes from it looks as though he may be foiling ahead of wave crests for more than half the time, although difficult to be sure of that from the video. If that is so then the water flow relative to his foil will have an upward component of velocity and depending on the drag angle of his foil system that could enable him to stay up with reduced or even zero power input. I found another video of someone with a foil equipped SUP and in that case they were obviously riding on the front of a wave.
     
  14. daiquiri
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    daiquiri Engineering and Design

    You are correct, there is probably that contribution too. But, he is also visibly pumping the board with his legs. :)
    Any of you guys remembers this? https://www.youtube.com/watch?v=k8Yv248B2-Y
     

  15. Skyak
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    Skyak Senior Member

    The vast majority of the thrust he gets is from wave energy. It would take a huge amount of wind, far more than available that day. The cool part is he appears to be able to transfer from one wave to another when there are intersections/interference. The paddle is misdirection. This is foil surfing.

    The more significant points in my mind are that the reduced drag of foiling means that surfing no longer needs the steep waves of shallow water! On a day with significant swell you can ride great distances off shore. The other point is that the foil appears to be a simple injection molded part -manufacturing cost is in the tens of dollars, not hundreds! The is a company here that makes parts from 3D printed molds. Do you have a 3D file? I will get a quote.
     
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