Pedal Powered Boats

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

  1. Guest625101138

    Guest625101138 Previous Member

    I was a bit more concerned about the fate of a 3mm shaft carrying the weight at the stern of the boat as it was being ridden up a log or rock. I have found it has to be very robust with ability to support the weight or compliant so it just flexes out of the way. The Cadence is on the robust side and not overly large to add to drag.

    In the 2005 Murray Marathon the fastest +50yo fellow hit a log with his rudder and the back of the blade punctured the hull. He managed to finish but the boat was half full of water.

    There are lots of ways to cause damage and it seems one of the issues with PPBs over paddles or oars is the prone nature of underwater bits. It would be nice to have a 90% efficient jet drive.

  2. beppe
    Joined: Jul 2008
    Posts: 51
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    Location: Udine, Italy

    beppe Junior Member

    Open Waterbike drive system

    Thank you Mark for your contribution to The Open Waterbike Project
    I’ll send your draft to the Open Waterbike members; ours is a small (but growing) community and we have already a few members with manufacturing capabilities scattered around the World.
    Meanwhile we will discuss modularisation, but is seems to be straightforward for the catamaran architecture and easy also for the a monohull architecture. Moreover, the principle of one-to-one function-component mapping is respected.
    Rick Willoughby 'offset shaft' is a way to address the hull-shaft interference solving one of the modularization problems and also a couple of practical issues, as he explains in one of the following posts.
    Anyway they are minor points; I believe your proposal could be a major step forward in this early phase of the Open Waterbike Project.
    Thank you again!
    Giuseppe ‘Beppe’ Carignani
    Funder, The Open Waterbike Project - ‘Our boat is faster than mine’
  3. MLampi
    Joined: Aug 2008
    Posts: 74
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    Location: Bellevue, WA

    MLampi Junior Member

    Hi Rick,

    I guess the stories of some of the details of the open water races between rowed, paddled and pedaled boats didn't get published as well as they could have been.

    There is a very strong rower in our club who normally rows one of his three double shells with either his son or another strong rower, and is very competitive. Several times he has managed to row over reefs, rocks, buoys, and even into the broad side of an anchored yacht in his zeal to win.

    He and others have often broken the small skegs on the bottoms of their shells that help the boats track in straight lines, sometimes with extremely disastrous results as the skeg cuts through the carbon hulls like a knife through butter.

    It doesn't help that his $10K+ shells just don't seem to be quite up to the task of staying in one piece during these mishaps.

    There are also many stories from the surf skiers in this area complaining about catching weeds on their rudders, even on the swept back "weedless" style. They also talk about switching rudders depending on the size of the waves they encounter. Some folks even carry different sized rudders with them, so they can switch them out as conditions change - or if they happen to lose one due to mishap.

    Of course, in the less competitive world of sea kayak touring, most of the boats have kick up rudders and absolutely nothing but hull below the waterline.


    Michael Lampi
  4. beppe
    Joined: Jul 2008
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    Location: Udine, Italy

    beppe Junior Member

    Open Waterbike: our boat is faster than mine

    Mark Drela's drive system with its incredibly thin shaft is just another demonstation that 'invention' and 'innovation' (the successful diffusion of invention) are different issues indeed.
    Rick Willoughby amazing 'unsupported shaft' and 'dipping rudders' are also beautiful achievements; we hope that the Open Waterbike Project will prompt the diffusion and improvement process
    Following the principles of openness we will try to diffuse them keeping them open and preserving the acknowledgment original (Mark's and Rick's) paternity of the invention.
    Rick, have you a draft of the same kind of that provided by Mark, including also your name?
    The Open Waterbike Project has already turned in an unexpected way, it seems that we will have to throw to the wind some extablished knowledge about drive units, but this is always the case with radical innovation.
    Also, it shows the Open Waterbike catchprase 'our boat is faster than mine' in action. It seems that our boat will be 'much faster than mine' and this is just great!
    Thanks again Mark and Rick!
  5. I57
    Joined: Feb 2008
    Posts: 172
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    Location: Melbourne, Australia

    I57 Senior Member

    Keep it simple

    Markdrelas drive system looks great, it keeps the drive very compact with the minimum amount in the water. A bigger prop with a 4:1 gear ratio is the most efficient but makes for a large prop. What is more efficient, a large more efficient prop with higher drag or a smaller less efficient prop with less underwater drag? The smaller prop has the advantage of a lower draft and able to launch in shallower water.
    I am thinking of a monohull similar to a rowing shell but a bit wider with the 10:1 drive unit connected to a flexible shaft and fixed at the prop with a skeg this would have a prop of say 200-250mm. The boat would be a complete unit ready to go and small and light enough to be carried on a cars roof rack.
    Rick, my boat is ready to go again but waiting on the weather.
  6. Guest625101138

    Guest625101138 Previous Member

    I am at the lake most Saturdays and some Sundays now. Just trying to build a bit of fitness.

  7. Guest625101138

    Guest625101138 Previous Member

    At 150 watts there is probably about 2W difference in the prop to the advantage of the larger prop. The difference in shaft losses would offset this.

    I find having the prop beside me and able to flip up out of the way is a bonus. You simply will not operate in the lake at the present time unless you can easily inspect and clean the prop.

    A prop under the hull without any protection for the shaft is bound to be fragile.

    The 10:1 gearing will be harder to get. It will not be bicycle components. The gearbox could be smaller and cheaper than one for 4:1. A 9mm shaft would be more than adequate. Only issue will be the radial load on the input shaft. It may need an outboard bearing to provide sufficient support.

    There are swings and roundabouts. Most people take a second look when the see the 1/4" shaft so a piece of thick wire would have them really wondering.

    One thing I have not checked is the torsional rigidity. It might feel very rubbery.

  8. markdrela
    Joined: Jun 2004
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    Location: MIT Aero & Astro

    markdrela Senior Member

    Not as hard as you think. See
    You can get 1/4" pitch chain hardware from lots of outlets.

    A thin shaft is relatively compliant in torsion, but this is not a drawback we found. One effect is that it smooths out the prop's RPM/torque variation if the legs' speed varies over the pedal cycle, which improves prop efficiency. It does feel "different" than pedaling a bike, but it certainly doesn't cause any direct mechanical losses.

    A uniform RPM like on a bike would of course be ideal. But this would require a substantial flywheel on the high-speed side at the gearbox, which probably isn't practical.
  9. Guest625101138

    Guest625101138 Previous Member

    The torsional rigidity has a large bearing on the ability to apply power unless you are a well trained cyclists. It has a large bearing on the overall biomechanical efficiency for most riders. There would be very few who have trained with springy systems long enough to cope well. It feels very awkward when extreme.

    I did the numbers for an 8mm aluminium shaft and the RMS power is quite a lot higher than the average power for most people once you start to apply a reasonable power level.

    I have set an acceptable limit of 7Nm/rad for my shafts spring constant at 4:1. So at 10:1 the torsional stiffness should be above 2.8Nm/rad on this basis. The 3mm shaft at 8ft long is 0.25 so would be unacceptable to most for any reasonable feel.

    If you get above 7 the feel is tolerable for cruising power level of 120 to 150W at 4:1 and design cadence of 80. If you are trained to spin at higher cadence, so design torque is lower, then 7 is quite good. Greg K can do 1000m sprints at 15kph with his 1/4" shaft and this requires 280W average. The spring constant is 11Nm/rad.

    For my sprinting I like a stiff shaft. The torsional rigidity above 20Nm/rad. Once you get to levels like this the feel is virtually the same as road cycling. There is no notion of rebound through the dead spot.

    Rick W.
  10. Guest625101138

    Guest625101138 Previous Member

    Engine Tuning

    Started the slow process of de-coking the old engine to day. Spent 2.5 hours on the lake holding heart rate around 150bpm. Attached chart shows the result.

    Weed is still a nuisance in the little lake but it was an incredibly balmy spring day for us here. Just about the perfect day. Quite often glassy smooth and occasional breeze to 10kph.

    I expect I am about 20W down on my average condition but a few more weeks on the boat and a bit of running will get me back into some level of fitness.


    Attached Files:

  11. Tiny Turnip
    Joined: Mar 2008
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    Location: Huddersfield, UK

    Tiny Turnip Senior Member

    The 24 hr HPB record dashboard on Adventures of Greg is looking very promising, Rick. Baited breath here...
  12. Guest625101138

    Guest625101138 Previous Member

    I am just making a post on the pedal powered thread. He got the record with 10 minutes to spare but they have stopped updating so I do not know the exact finish.

  13. Guest625101138

    Guest625101138 Previous Member

    New World Distance Record

    Greg K managed to better the world record for distance covered on water in 24 hours. He passed the old record, set on a surf ski by Carter Johnson, with 10 minutes to run. The old record was 242km and Greg was heading for 245km.

    Exact distance is yet to be confirmed but he aimed to claim both IHPVA and Guinness records. It could be a silly situation where they are different distances because one allows GPS indication while for the other it must be over a marked course and he has to have some clearance to the buoys. Still to see the end results. No doubt he is in recovery mode.

    He maintained a very steady pace with average in the first few hours around 10.8kph dropping to 10.2kph at the finish. He had a little left because pace picked up a bit toward the end.

    Rick W.

    Attached Files:

  14. Tiny Turnip
    Joined: Mar 2008
    Posts: 747
    Likes: 179, Points: 43, Legacy Rep: 743
    Location: Huddersfield, UK

    Tiny Turnip Senior Member

    Well Done Rick!

    Rick - huge congratulations on what you have achieved with the rest of the team - absolutely fantastic!


    very best


  15. Guest625101138

    Guest625101138 Previous Member

    I did the engineering. Greg built the boat and was the perfect engine. He also persevered to get it as good as possible.

    I doubt that anyone else could hold their nerve as well as he did over a 24 hour period. The strategy was to hold a constant speed and he very nearly managed that. Initially he would have been well within himself so he could stay nourished.

    The weather played its role as well. The beginning had a little more wind than you would like but the evening and early morning were calm. Under those conditions the boat just glides and this would be encouraging.

    Now when do you get your boat in the water for first trials?

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