Pedal Powered Boats

Discussion in 'Boat Design' started by Guest625101138, Jul 14, 2008.

  1. Guest625101138

    Guest625101138 Previous Member

    It certainly has been thought about. Some examples here:
    http://search.gmane.org/?query=elec...culture.transportation.humanpowered.boats---A

    Not sure if anyone has actually tested it. Usually once the numbers are crunched it does not stack up.

    With the best system you could make, about 40% of the input power would be lost in the mechanical-electrical-mechanical conversion. This cannot be made up by any benefit the system might offer.

    There may be some advantage if you were going to battery storage to do a high speed sprint for example. So energy is stored over a period of time and then delivered in a shorter period.

    The neatest low drag set up is a single gear reduction of 3 or 4 :1 driving a curved shaft.

    Rick W
     
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  2. Jeremy Harris
    Joined: Jun 2009
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    Jeremy Harris Senior Member

    Rick's right, it's inefficient.

    I did a few calculations a week or so ago to see just how big the losses would be for such a system, as it came up in a conversation about my electric boat project (which uses a hull that was originally pedal powered).

    Some losses are effectively the same for direct drive or human-electric series hybrid drive; shaft bearing losses, pedal bearing/gearing losses and propeller losses. These can be discounted from the comparison, as they balance out.

    The electric motor will be about 85 to 90% efficient, as will a really good alternator, plus you'll lose another 5% or so in the wiring and control electronics. If we assume that the input power from the pedals to the alternator is 100 watts, then you might get something like 85 to 90 watts of electrical power out of it. You lose maybe 4 or 5 watts in the wiring and electronics, so have maybe 80 to 85 watts available to drive the motor. The motor loses about another 8 to 12 watts, leaving between 68 and 76 watts of mechanical power to drive the prop, most probably around the lower end of that range.

    The comparison is with a shaft, that will have no appreciable power loss.

    The advantage of such a system is the ability to use a battery to store energy, allowing the pedaller to generate more electrical power than is needed for a given speed, storing it up to give a boost, or allow a pedalling break to be taken.

    Jeremy
     
  3. portacruise
    Joined: Jun 2009
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    Location: USA

    portacruise Senior Member

    This principle has been done for a road bike (NOT boat) and was considerably more efficient than I would have ever expected. A prototype was demonstrated at a Swiss conference many years ago. A chap by the name Theo Schmidt from the Human Powered Vehicle power assist list was involved in the development, if I remember correctly. This question comes up periodically and here is what I wrote some years back:

    "There was a power assist list discussion sometime back was on
    generator-motor drive which I call "selsyn" drive. This had been developed
    to quite a high efficiency ~80%+? for land vehicles and even allowed for
    electronic gear shifting. Essentially no battery storage- use as you
    generate configuration. Theo Schmidt of this list was involved with some of
    this I believe.
    The greatest attraction in water would be ergonomics and ability to
    configure pedaling station to just about any position (recumbent, upright
    etc). You might even be able to make the station like a portable exercise
    machine which could be moved inside your cabin for inclement weather and
    yet still use pedal power to run the motor unit via the electric wires.
    Using the generator to pedal up batteries to charge is notoriously
    inefficient unfortunately, maybe ~5%? (due to losses: mechanical>
    electrical>chemical>electrical back> mechanical)from what I read. But you
    might be able to use excess sail power to spin your normal driving prop to
    charge batteries like in tow behind generators. Much of this in the power
    assist archives. Anybody know how to access them directly without having to
    be a list member?"




     
  4. portacruise
    Joined: Jun 2009
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    portacruise Senior Member

    Here a reference paper by Fuchs which might be interesting for those that want to pursue the chainless electrical transmition:

    http://www.hupi.org/HPeJ/0015/SeriesDriveHybridVelomobiles.pdf

    Google Andreas Fuchs for other references.

    Enjoy.

    Porta



     
  5. Jeremy Harris
    Joined: Jun 2009
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    Location: Salisbury, UK

    Jeremy Harris Senior Member

    Charging some types of battery can be inefficient, lead acid, for example, is probably amongst the worst. Lithium batteries can be pretty good in terms of power out for power in efficiency though.

    I have a task to look at charging from sail power. At the moment it doesn't look to be too efficient if the same prop is used for both propulsion and charging. Ideally it needs a bit bigger turbine for charging than it does prop for propulsion. It might still work though, and is easy to implement. The motor controller I'm using on my electric boat has a built in regeneration capability, so it will automatically switch to charge mode if the boat were to be towed, or moored in a strong tideway, perhaps.

    80% efficiency for a human powered hybrid sounds achievable if everything is optimised. My guess is that 70% is closer to the performance of a practical real-world solution, though.

    Jeremy
     
  6. portacruise
    Joined: Jun 2009
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    portacruise Senior Member

    Jeremy, here's a typical commercial tow behind:

    http://www.onpassage.com/Alternative_Energy/Water_towed_generators.htm

    Porta

     
  7. Guest625101138

    Guest625101138 Previous Member

    I finally made my folding prop. The operating point is 11kph for V14.

    I took it for a run on Saturday and was pleased. It was difficult to get accurate performance data in the blustery conditions with wind gusts over 70kph and steady 30 to 40kph breeze. It was quite easy going down wind at the top end of the lake but speed slows up as the waves get bigger and it becomes hard climbing over them. Going back up, I progressed quite slowly until up the lake and the waves were not dunking me to the same degree. Overall I managed 21km in a little over 2 hours.

    If the prop collected any weed I only had to stop spinning and it would flow off the trailing blades. When both blades fold they stop each other at about 30 degrees but if a single blade folds it goes to almost inline with the shaft.

    The blades spread very easily, probably around 20rpm.

    I am looking forward to some calm weather so I can make a more accurate assessment.

    The blade chord is quite small so they fold neatly. They will flex under full effort but not problem up to about 15kph.

    Rick W
     

    Attached Files:

  8. Jeremy Harris
    Joined: Jun 2009
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    Jeremy Harris Senior Member

    Very neat, Rick. I'm really pleased that you've found that these blades shed weed easily when folded, as that's only of the main issues I'm trying to overcome.

    I look forward to seeing just how it's performance compares with your fixed props.

    Jeremy
     
  9. Guest625101138

    Guest625101138 Previous Member

    Jeremy
    If you go back to post #299 you will see similar data for my fixed bladed prop. This was not quite as windy and on a narrow rowing course where waves were never more than a few inches. I collect this sort of data so I can make comparisons.

    Yesterday I was contending with waves half a metre or so down the bottom end of the lake. If I drove hard into them I would get drenched. Every now and then one would wash into the seat.

    I doubt if you could pick the difference in the performance if the upwind leg is not considered but I need calm conditions to do more accurate comparison.

    I have found that I get the best average speed in calm conditions. I have also found I can go faster in calm conditions than going downwind in any waves. The wind helps in the waves but it is not easier than dead calm with no wind.

    I can do a little better with the blade shape around the hub yet but this does not contribute much thrust. I normally polish up after the first test if I am happy.

    The hub took about 1 hour to make from 40mm 2011 aluminium and the blades about 2 hours from 316 stainless. I spent a little time fitting the blades to the hub as well. Being so small there was not much grinding involved in shaping the the blades. The 2011 is not the best for saltwater. I would go for a stainless hub if corrosion was a concern.

    The other nice feature with the folding prop is the ability to coast. It is nice to stop pedalling and to keep gliding. I can still go astern by spinning enough to throw the blades out.

    Rick W
     
  10. MLampi
    Joined: Aug 2008
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    Location: Bellevue, WA

    MLampi Junior Member

    Human powered boat race yesterday

    The West Seattle Blog had a photojournalist at the Great Cross Sound Race yesterday and he put together a nice video which includes some race footage and an interview with race director Jeff Knakal about the race and its history.

    http://westseattleblog.com/blog/?p=20039

    I'm in the video, the blog and in one of the Flickr photos.

    My time was not especially great as I was fighting the ebb tide more so than the rest of the field by doing the course in reverse. Still, I took nearly 700 photos and most turned out. :)
     
  11. portacruise
    Joined: Jun 2009
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    portacruise Senior Member

    Kudos on the folder, Rick! Nice looking bugger, too.

    One additional advantage with the folder especially with a strutless flex shaft might be improved shallow water operation.



    Porta

     
  12. Guest625101138

    Guest625101138 Previous Member

    Mike
    I needed to turn off HD to see the video.

    What was your time?

    Rick
     
  13. Guest625101138

    Guest625101138 Previous Member

    Porta
    The idea for the folding prop came from the IHPVA site after discussing my 2008 Murray Marathon encounter with logs. I expect the blades will fold if they hit something solid. The shaft strut is quite flexible so it will bend away from solid objects.

    Rick
     
  14. Jeremy Harris
    Joined: Jun 2009
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    Location: Salisbury, UK

    Jeremy Harris Senior Member

    Rick,

    That's excellent if it really is close to the same efficiency as your fixed blade props, as I think you've already got pretty close to the best prop design for this low-power application with those.

    Out of interest, what thickness stainless did you use for the blades?

    I have a bit of 1/8" (3.2mm) 316 sat in the back of the workshop and am wondering it it would be man enough. I guess I could silver solder some bracing to the root area if you reckon that 1/8" is a bit thin.

    Jeremy
     

  15. Guest625101138

    Guest625101138 Previous Member

    Jeremy
    I use 3mm for most of these small blades. I usually weld a triangular section at the root of the blade to stiffen it up and blend it into the target profile. The blade chord is 25mm so it is a relatively thick blade.

    With the ones I get milled I use defined sections but the hand fabricated ones the transition sections are done by eye. The root of the blades do next to nothing. It is there primarily to reduce induced drag over the working part of the blade.

    Any more info and I will be giving away my secrets. I guess I am a bit like you and your aircraft props, I use JavaProp for a first pass and then do the proper design with my own design tools. I keep refining these as I take more detail into account.

    Rick
     
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