Flapping inverting foil (patent pending)

Discussion in 'Boat Design' started by frogger1225, Sep 7, 2014.

  1. johnhazel
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    johnhazel Senior Member

    Wellllll.... since the chart you are using refers to cyclists and my example is for canoe paddlers.... No.
     
  2. frogger1225
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    frogger1225 Junior Member

    According to fig 12 of the article you presented, it shows that after a couple minutes, rowing activities had a higher capacity than cyclists. Assuming canoeing is similar to rowing (just for argument sake), this would imply that efficiency is even less the ~60% number that I mentioned previously.

    On second thought it really doesn't matter, I'm getting old and this discussion has no unique unqualified answer. OK it's 1/8 HP.
     

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  3. johnhazel
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    johnhazel Senior Member

    Rowing vs Paddling, again apples-to-oranges, maybe not chalk-and-cheese but still two different things.
     
  4. frogger1225
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    frogger1225 Junior Member

    Here is something I found that hits the heart of the problem. The human is the cause of inefficiency in canoeing, not the paddle. Or is it that the paddle is not properly designed for the human so that it can be efficient for both the expert and the novice.
    http://www.piragis.com/newsletter/canoestrokeefficiency.html

    My FIF blade and simple system to utilize it is simple push-pull(back forth) with no other complicated pitching heaving or other manipulation.
     
  5. Jeremy Harris
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    Jeremy Harris Senior Member

    I don't think you've read all the work published here on low speed props and pedal power. Well worth reading, especially all the work and measurements made by Rick Willoughby, as it clearly disproves your assertion.

    Rick put an awful lot of effort into building fast and reliable pedal powered craft (and still is, but he no longer posts here, regrettably). The fact that he can pedal his boats at around 12 to 15 kmh continuously, and has completed in long distance endurance events (like the Murray River Race) successfully, pretty much proves that propellers are a good match over a fairly wide range of conditions. Certainly a 2 to 1 speed range has little effect on efficiency for a well designed prop, the secret is getting the hull drag down at higher speeds.

    One of Rick's designs was used successfully for a 24 hour record by Greg Kolodziejzyk (see here: http://adventuresofgreg.com/blog/2008/09/15/24-hour-hpb-record-report/) and had to work over varying speeds and power levels (because the wind makes a fair difference to the power needed).
     
  6. Jeremy Harris
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    Jeremy Harris Senior Member

    Not quite. If you can match the bodies max continuous aerobic output power to a device that can convert that power into useful true propulsive power (i.e thrust x speed) with minimal losses then you can get a fair bit better performance.

    Measurements made on oar efficiency show that it varies wildly, from 30% or worse for poorly matched oars on something like a rowing dinghy, to over 60% on a well-designed sculling boat with long oars and a good match between scull blade peak velocity and boat speed. Paddles are pretty similar, with the best paddles being pretty close to the best oars in terms of efficiency.

    A propeller, or a paddle boat, can achieve higher overall efficiency, primarily because of the reduced losses from not having poor efficiency at the start and end of each stroke. Mid-stroke oar or paddle efficiency is pretty much the same as that of a very good propeller or paddle wheel, it's the accelerating initial part of the stroke and the decelerating finish part, plus the zero efficiency return of the paddle/oar to the start position for the next stroke, that causes a fair bit of the additional loss.

    There are a lot of other factors to consider when looking at all the causes of lost power in a propulsion system, including bearing losses, which can be significant at the low power levels of any human powered system. I found that it was easy to lose a few watts in bearings and seals, for example, and when you've only got 100 W or so to start with that is significant. Reducing all the small losses, then getting the very best hydrodynamic efficiency possible from the device that is generating thrust is the key to being able to get maybe a 10 to 20% improvement in propulsive power over oars or paddles, and is clearly a worthwhile gain. Few have managed it though, and the only really efficient systems I've seen have been either large diameter, slow rpm, high aspect ratio water props, or even larger diameter air props (like Decavitator, for example).
     
  7. frogger1225
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    frogger1225 Junior Member

  8. johnhazel
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    johnhazel Senior Member

    The typical racing stroke has a much shorter power phase than described in the piragis article. The power phase ends very close to when the bottom hand passes the knee of the paddler. In our racing boats, if you paddle as described in that article you would be flopping left and right. Your paddling partner would start complaining after about 5 strokes ....
     
  9. Jeremy Harris
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    Jeremy Harris Senior Member

    Yes, but not the farcebook link, or the Youtube link, that's someone else

    He has many thousands of posts here, too, but since he left the forum he appears as "Guest625101138". The massive "Pedal powered boats" thread here ( http://www.boatdesign.net/forums/boat-design/pedal-powered-boats-23345.html ) has a wealth of really excellent information in it on efficiency, design, development and practical testing and performance measurement.
     
  10. frogger1225
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    frogger1225 Junior Member

    (Timeout for forum re-calibration)
    Template for problem statement:
    How to move payload (cargo/passengers) from point A to point B (short distance/long distance) in time (quickly/slowly) with obstacles (portages/no wake zones/shallow depth) using power source (passenger/petro/thermal/photon(solar)/wave/nuclear) via transmission method (mechanical/electrical/hydraulic) to power converter (prop/oar/paddle/mirage drive/FIF blade) to propel boat
    Never too old !!
    http://youtu.be/6E_SX9gPJbM?t=52s
     
  11. daiquiri
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    Location: Italy (Garda Lake) and Croatia (Istria)

    daiquiri Engineering and Design

    Frogger, I have checked your videos. Have to say that, of all the ways to make a flexible oar, you have found a possibly least efficient one. Good as an exercise for the arms, dorsal and pectoral muscles, but very inefficient as a propulsion device. You are producing a lots of side force and very little forward thrust.
    I am sorry to hear that you have wasted your money on patenting that stuff. :(
    Cheers
     
  12. portacruise
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    portacruise Senior Member

    Rick still posts to the Human Powered Boats site a few times per year when he has a new model, or on some new developments, races, etc. The HPB list is very low volume compared to past years, but some good info is available in the archives.

    Rick manufactures and sells very efficient folding props that appear to be tuned to a specific range of lightweight/streamlined racing style boats. Not sure those props would work well on heavier canoes, sailboats, dingy, etc.

    PC

     
  13. frogger1225
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    frogger1225 Junior Member

    Can you point out lots of side forces in the attached pic? If not watch the video link. Lights out!
    http://youtu.be/cWEmSn9BbYc.
     

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  14. wavepropulsion
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    wavepropulsion Pirate Member


  15. frogger1225
    Joined: Aug 2014
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    frogger1225 Junior Member

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