Paddle vs. Pedal?

Discussion in 'Boat Design' started by KalleA, Mar 28, 2009.

  1. KalleA
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    KalleA Junior Member

    Reading about Greg Kolodziejzyk's 24 hour world record got me thinking. Greg K covered some 245 km in a pedal/prop boat vs. Carter Johnson's previous record of 242 km in a surfski kayak, i.e. virtually identical performance. I would have expected the pedal/prop boat to be more decidedly faster and I wonder what the differences between the two concepts really are, adjusted for weather and engine differences?

    I hope someone with real know how will pitch in, and this is just an attempt to outline some issues for comparison (most quantifications I have gathered from this amazing forum, so apologies if I've gotten them wrong and credit to Rick W if they're right):

    1. Biomechanical efficiency
    I gather paddling and pedaling are pretty similar at around 26 %?

    2. Mechanical losses
    0 % for paddelling and 3 to 4 % for pedals.

    3. Propulsion efficiency
    72 % assuming an excellent paddler (?) and 87 - 88 % for the prop.

    4. Concept specific drag
    I guess the propshaft produces some drag? Does the side mounted prop result in any turning motion that needs to be trimmed/counter steered?

    5. Aerodynamic drag
    The more upright paddling position as well as the paddle moving through the air should be a relative disadvantage for the kayak, but perhaps miniscule at the speeds and weather conditions in question?

    6. Hull shape. My initial thoughts were that the pedal concept should allow for a longer, sleeker, more efficient hull than the surfski, but perhaps this is cancelled out by the outriggers?

    Not sure what I might have missed and/or gotten wrong, but it would seem to me that the pedal/prop concept should be more superior to the kayak than the 3 km difference indicates, and that differences in engine capacity and specific weather conditions would explain that?

    Cheers
     
  2. Guest625101138

    Guest625101138 Previous Member

    One factor that is somewhat elusive is water temperature. Whitefish Lake gets frozen I believe and I expect was cooler than California. Choosing early autumn for Greg's run was considered to give the best water temperature for the location but warmer water would be better.

    Another subtly is the shaft. Greg used a 1/4" (6.34mm) shaft. The ideal is more like 8mm. What this means is that Greg had to train muscles and concentrate to cycle. The thicker shaft provides significantly higher torsional rigidity (4th power of dia) and takes less concentration to keep smooth prop operation.

    Greg feels age does not make much difference in these events but I understand Greg has quite a number of years on Carter.

    Greg had an outrigger loose in the morning light but does not know how long it had been flopping about. He suspects it was for a number of hours and you can see how he fell off through the night. Always hard to know without more engine data during the run to pinpoint any specific boat problem.

    I am highly biased here but I feel an average of 11kph would be achievable with a younger trained pilot. I guess time will tell. On the other hand I believe Carter feels he could do better than Greg has already achieved. For now Greg is the benchmark. Greg's average output for the run was about 110W. If you look at what world class cyclists can sustain over 24 hour runs then it is more like 200W. Put this into a boat designed for that power and the result would be over 13kph - 312km in 24 hours. Then you have to ask how close is Carter to a world class athlete.

    I cannot see how a paddled craft could do better than a pedalled boat. The only advantage of a paddled boat is that it can be built lighter because there is no drive to worry about. The best possible pedal boat would carry a 3 to 4kg disadvantage in this regard. However it means any recumbent cyclist can get on the boat and immediately feel at home. It takes many years of training to achieve the paddling efficiency of a good kayaker. Every stroke has to be done with precision. This is much more difficult task than just rolling the legs over.

    Rick W
     
  3. jehardiman
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    jehardiman Senior Member

    Rick points out most of the tradeoffs between pedal-prop and paddling, and like him, I believe that in a long distance event, the prop has an advantage. He also points out, correctly I believe, that long term power is limited by muscle mass oxigenation. i.e. the legs are stronger, but they use more oxygen and waste more energy just because of thier mass so in the end it is a near wash. In HP submarines, it was easy to go anaerobic with either arms or legs only.

    The only place where paddled-oared may have it over pedal-prop is in short sprints. This is beacuse the effective thrust is immediate and ameaniable to "over speeding". FWIW. props are not the end-all for propulsion, there are situations where paddle-wheel, air props, and cyclic rowers have thier usefulness.
     
  4. sigurd
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    sigurd Pompuous Pangolin

    Hi, jehardiman,

    can you elaborate on the advantages and disadvantages of paddlewheels and air props please? And, what is cyclic rowing?
     
  5. Guest625101138

    Guest625101138 Previous Member

    John
    I am reasonably confident that the prop will accelerate faster. I can easily outaccelerate a kayaker. Rowing might be a bit harder but still think the prop would be better. So a 100m drag race would see a prop in front.

    The olympic 2000m events would make an interesting comparison for rowing and pedal. Greg could hold 15kph over 1000m and I know a young rider who can hold 16kph over 1000m on my boat. This is getting into rowing scull territory.

    The numbers show a boat optimised for an olympic sprint cyclist over 2000m would outperform an olympic rowing scull. It would be an interesting comparison.

    The fastest human powered boat was pedal powered and prop driven. It achieved close to twice the speed of a rowing scull but only for 100m.

    Rick W
     
  6. KalleA
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    KalleA Junior Member

    What produces the 4% disadvantage of rowing? Does it relate to the return stroke and returning the body to the forward position (assuming a sliding seat configuration)? Does this take into account the oscillation (boat bobbing longitudally as a result of the moving centre of gravity) induced work, i.e. that the sliding back and forth involves some horisontal movement as well? If so, is there any data on differences in biomechanical efficiency between sliding seat and sliding rigger configurations?

    I remember from somewhere that the propulsion efficiency of rowing is around 64-65 % on flat water, deterioring significantly when it gets choppy. Can one assume that the prop has a slight advantage over the paddle in rougher seas?

    On the topic of biomechanical efficiency: what is the efficiency of a swing arm system with a top mounted pivot? In your Pedal Povered Boat thread (Post #80) you mention that the efficiency is higher than for a crank - do you have a number/estimate of by how much?

    What sort of mechanical losses can one expect in the roller clutches?

    In addition to the nice motion, I can imagine other potential advantages of the swing arm solution:

    - Feet/legs are lower down = lower COG.

    - The lower foot position might generally be good for the body hydraulics (?) and or allow for a more reclined position whilst still having the pump above the feet = further lowering of COG and possibly better aerodynamics

    - As the configuration is narrower at the top, a more aerodynamic fairing might be possible (?)

    Then again, the higher oxygen content of the cooler air should be good for the engine...

    All in all, it seems that you have come a very long way in optimising the pedal/prop concept. Where do you see potential for further improvement?

    Cheers
     
  7. jehardiman
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    jehardiman Senior Member

    Unless you are talk about a large wheel, the paddler has it all over a wheel. When we looked at setting the submreged speed record through a trap, we did some measurments and investigations because we had so much mass to accelerate. A 0.8M dia CR prop set turned by a professional cyclist generated 200 lbs thust at bollard, but it quickly droped off as speed was gained. A paddler with a optimized (~0.6 m^2 CF) paddle generated approximately 300 lbs, but maintaind that thrust until thier arms could not move fast enough.

    That is the real issue. Basically, the thrust of a paddle or oar is maintained until the biomechanics of the lever cannot keep up, because the thrust of the blade is effectively equal to the drag of the hull. For a wheel, thrust is only proportional to J, which for human propulsion can use gearing to optimize delivered power.
     
  8. jehardiman
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    jehardiman Senior Member

    To be very efficient, HPV marine props must be large and thin. This leads to several major problems, draft, tip speed, and bending moment being the most common. As I have said, we used a 0.8m CR set , and other fast subs used wheels at least 0.5m or better. A 1m wide, 1.5m paddle wheel could replace these props with only a draft of ~0.1m, and an 2-3m air prop (which has the same problems as a marine prop BTW, see MIT's Decavitator HPV) could have even less draft. All propulsion systems have advantages and disadvantages, you need to get the best one that suits your needs.

    A cyclic rowing machine is like FrontRower and some other more obscure designs that use a fixed seat and leg/arm power to operate a rowing, sculling (oscillating foil like the Hobie Mirage system or Scripps SubDUDE HPV), or paddleing system.
     
  9. sigurd
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    sigurd Pompuous Pangolin

    Thanks. Curious why Decavitator uses air prop and Rick W. and most others use water props.
    The SubDude device sounds interesting. Got pics?
     
  10. KalleA
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    KalleA Junior Member

    Looked up the FrontRower. What an interesting solution:

    http://www.frontrower.com/aboutfrontrower.htm
    http://www.patentstorm.us/patents/5685750/fulltext.html

    Does anyone here have any hands-on experience with, or qualified thoughts about, the FrontRower?

    Surely, a pedal/prop will be more efficient, but the FrontRower raises some thoughts:

    1. Biomechanics
    It could be more efficient than a sliding seat rowing setup since the body, like on a sliding rigger, does not move back and forth. Leg power is transmitted directly (not through back/arms/hands) via a nice top pivoted swing arm action. For anaerobic sprints, one can still use the combined power of both arms and legs. So, without knowing the specific ins-and-outs of the FrontRower, it might have some advantages over traditional rowing?

    It just strikes me that there might be a biomechanical component related to the forward vs. backward facing rowing position: constantly twisting your neck! I HATE this about my single sculler - you're constantly turning your head and still not 100 % sure where you're heading and when you'll decapitate some poor swimmer or ram into something... One of many reasons for looking into pedalboats.

    2. Mechanics
    There are a few cables, pulleys and return springs involved, so I'm guessing some mechanical losses, 1 - 2 %?
    It seems as if most forces acting on the chassis would be straight tension and compression, but still, given the dynamic loads, the wooden structure might be less than ideal?

    3. Propulsion
    In flat water, probably similar to the 64 per cent of traditional rowing, but I can imagine that it suffers even more in rough seas, given the automatic lifting and feathering of the oars? It took me a while to undestand how this works btw, but it's really pretty nifty and clever.

    4. Other
    The FrontRower seems to have similar ease-of-use qualities as the pedal/prop - not too much technique, just pedal away.

    I like the way you can drop the whole FrontRower assembly into an existing hull (like a narrow rowing boat or a canoe) with apparent ease of installation. Does something similar exist as a concept or a commercial product in the pedal/prop world? i.e. an adjustable seat/frame/pedal/prop assembly that one could bolt onto, say, a canoe? I guess an added complication compared to the FrontRower is that one would need some steering arrangement as well.


    Anyway, thanx for the heads-up, certainly interesting and different.

    Cheers
     
    Last edited: Mar 30, 2009
  11. Guest625101138

    Guest625101138 Previous Member

    I now have lighter and stiffer frame than Greg used. It is made from factory produced CF tube.

    Greg did not use the dipping rudders I now use. Once you get used to these they lower power by 2 to 3 watts.

    Viscous drag is the major loss. There are surface finishes and other surface treatments that can lower this. This is an area I have not explored seriously. If you had very deep water it would be possible to used submerged buoyancy effectively. This has potential to dramatically reduce surface area and thereby reduce viscous drag.

    A rider capable of holding 200W could sustain flight on foils at around 14kph. I looked at this very closely for Greg but it was beyond his sustainable power level. At 150W there was no benefit and his sustained level is even somewhat below this.

    Rick W
     
  12. KalleA
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    KalleA Junior Member

    I was looking at my carbon rowing oars recently, wondering if they would not be a material source for making a frame...

    Still surfing and searching around the forum, and just found the dipping rudders. Interesting stuff. What is your view on integrated rudders (like Epic and Mirage use on their kayaks)?

    You addressed something that was just on my mind. I used to be decent cyclist in my youth, but 200W sustained is quite a bit and certainly well beyond me these days. Still, for a hybrid with a very modest electrical engine this could be cool.

    Cheers
     
  13. Guest625101138

    Guest625101138 Previous Member

    I expect these have merit. Definitely worth considering as a trimming rudder at least.

    Rick
     
  14. KalleA
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    KalleA Junior Member

    Pendulum swing arems, reeving system, etc.

    Rick,

    sorry for swamping you with questions, but you are such an amazing source of knowledge and information. I feel like a kid in a candy store!

    I guess this is the ZRower concept?
    http://www.forwardface.com/

    Wondered why this had gone quiet. Sorry to learn about the inventor's demise.

    I must admit that I haven't quite figured out how the reeving really works, but am I correct in assuming that the prop is only turned during the power stroke and freewheels during the "return stroke"? If so, using swing arms rather than the original rowing setup, could one imagine a solution with two reeving setups in tandem, each connected to one of the swing arms, and set up 180 degrees apart?

    Not sure if this would work for the reeving system, but top pivoted swing arms w. roller cams ought to work for driving a normal chain and box transmission to a prop, right? A bit like this:

    If the motion is more biodynamically efficient and the rolling clutches have negligible losses, could this have some merit in a "normal" transmission, or am I missing something?

    Cheers
     

  15. KalleA
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    KalleA Junior Member

    Yeah, I remember that the sliding rigger was totally dominating the sliding seat boats in the early 80's. I believe FISA banned it because of the costs of re-fitting all rowing boats with sliding riggers in order to stay competitive. Perhaps the right decision from a sporting perspective, but it appears to have had a handicapping impact on all rowing boats. How often do you see sliding riggers compared to sliding seats on non-regulated and recreational boats? Almost never, I would say. And for no good reason, as the sliding rigger is clearly superior.

    If anyone is interested, this is an interesting take on the sliding rigger:
    http://www.rocat.co.uk/boat/rigger.htm

    Cheers

    P.S. Re. your reference to the fastest bicycle, part of my interest in PPB's stems from having two friends who always argue the rowing scull vs. kayak debate - one is a former Olympic class sculler and the other a former international K1 kayaker. It would be fun if their argument regarding the fastest HPB could be settled and demonstrated by an old cyclist...
     
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