Pedal Powered Boats

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

  1. portacruise
    Joined: Jun 2009
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    portacruise Senior Member

    Rick, I assume you are trying to guage the strength of the cone or blades under the pressure of forward thrust. Hard to say, without purposefully pushing forward on the blades to the point of failure. The particular one I chose has all plastic hinge and parts except for the hinge pin, yet has held up to 50 watts of drive power after 4 uses. Blades are fairly stiff. I believe the same exact setup is available with stronger metal yoke for the hinge, but the cone appears to still be plastic, so the the yoke may be the limiting factor, rather than the cone or blades? There was another website (available in Oz?) that had hand laid carbon blades I wrote you about before. It also carries high quality aluminum spinners if you look around on the site. Some of these may fit the fairly standard 8mm thick hinge that comes with most folding blades, possibly the 16.5" blades you found at Hobby Lobby.
    Hope this helps.

    Vic

     
  2. Guest625101138

    Guest625101138 Previous Member

    I photographed the belt drive I have fitted to the V14 boat. The belt is 10mm tooth pitch with a 60T drive and 15T driven pulleys.

    I have a slack side tensioner to reduce the initial tension. The belt is not preloaded to the recommended level because the low power losses would be more than a chain if I did this.

    It is very smooth and feels nice at normal cruising. It limits top speed to about 12kph as it jumps teeth above that level.

    The advantages it has over a chain is that it is clean, quiet and not inclined to corrode. The power limit is a bit annoying and I prefer the chain mainly for this reason. I will keep it on for a while to see how it lasts. It would transmit more power with bigger pulleys but they get to be an expensive option above this size.

    Rick
     

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  3. Dennis A
    Joined: Aug 2009
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    Location: Amersham bucks uk

    Dennis A Junior Member

    Belt Drive

    Rick I would recomend a small roller fitted adjacent to the small pulley on the slack side that is normally just clear of the belt and therefore has no drag. This should be close enough to the belt so that it prevents the belt riding up when it tries to jump the teeth. The support bracket would need to be strong as the forces are quite high.

    Dennis
     
  4. portacruise
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    portacruise Senior Member

    RC prop

    I used the Rc prop for a couple of hours on Saturday, and found that the plastic cone seems to be the weakest link, as you predicted. The blades pull forward with such force that the top section of the plastic slot collapsed slightly. The blades and hinges are holding well to this point, so I plan to rebuild and strengthen the slot area on the cone. The blades are quite strong for being of electric design.

    I experimented with different weed types and still got loose wrapping on the shaft. Beginning to think a much gentler elongated cone on the shaft would help for the stiffer weeds at least, as the spinner is just too short and wide.
    I tried one thing that might even paralyze your well designed folding prop, Rick. Pond scum seem to jam up the hinge slots, and accumulate a large ball in short order. This may not be an issue for the Murray, though. If so, you would have to clean by hand.

    Enjoy.

    Vic


     
  5. Guest625101138

    Guest625101138 Previous Member

    A friend took a short video of the V14 boat near full speed a while ago and I have added it to my gallery. It is interesting because it shows how the boat trims bow up at speed:
    http://www.boatdesign.net/gallery/data/500/V14_Rick_16kph.wmv

    The bow is normally immersed 20 to 30mm deep at rest. At 16kph it lifts level or slightly above the surface as is apparent in the video. It would have been better to video in calmer conditions but that can mean a long time waiting.

    The point is it shows that the flat bottom certainly generates some lift. This is not apparent with the semi-circular hull bottoms.
     
  6. Guest625101138

    Guest625101138 Previous Member

    Dennis
    I made a small PTFE roller that is mounted on a bolt that uses one of the holes in the gearbox flange. It is very rigid and just touches the belt at load. By removing the tensioner I ended up with the belt slightly slack.

    The end result is brilliant. The belt runs easier at light load without the tensioner and I took it up to 15kph today without any risk of skipping teeth. I may be able to go higher but I do not have a spare belt and I am getting close to its rated tension at 15kph.

    I will stick with the belt now and see how well it lasts.

    The little roller idea will also get incorporated into my electric drive.
     
  7. Dennis A
    Joined: Aug 2009
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    Location: Amersham bucks uk

    Dennis A Junior Member

    Spring Steel Drive Shaft

    Rick

    What grade spring steel do you recommend, and is this in its manufactured state or does it have to be hardend and Tempered.

    Dennis
     
  8. beppe
    Joined: Jul 2008
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    Location: Udine, Italy

    beppe Junior Member

    the future of pedal boats...

    Hello Rick and everybody
    it's a long time from my latest contribution to this thread, but I have followed it with great interest since then...
    I have just retrieved this picture I found months ago while researching the history of pedal boats, and thought you could be interested in it.
    The caption of the figure reads like this:

    "Apropos of the bicycle craze, it appears that the next thing in order is a machine of some kind that will be, in relation to water, what the bicycle is to land. The annexed engraving illustrates a machine which acts in relation to water as the bicycle does to a solid surface; that is to say, it gives the same opportunity for balancing, and depends on inertia for the upright position of the rider.
    It consists of three hollow cylinders with conical ends and driving and steering mechanisms. The outer cylinders are smaller than the middle one, and made of very light material, such as aluminum or paper. The middle one is made of galvanized iron or sheet copper.
    The rider mounts, gets under headway, then raises the lateral floats clear from the water and fastens them. After that he depends on his momentum for his upright position, as in the case of the bicycle. Should he lose his balance, the lateral floats will catch him and prevent accident."
    It's from Scientific American, Aug 24, 1895

    Fascinating, isn't it?
    I remember a number of subsequent inventions (most recent i believe was the Wavebike) successfully following the same principles of dynamic stability...

    As we can see, the prophecy of Scientific American (it appears that the next thing in order is a machine of some kind that will be, in relation to water, what the bicycle is to land) was not fulfilled, notwhitstanding the efforts of several generations of brilliant inventors and brave entrepreneurs.

    What went wrong?
    Any reason for believing that the future will be different?
    Any idea, anybody?

    Giuseppe 'Beppe' Carignani
    Founder, The Open Waterbike Project

    P.S. I don't know if this discussion is appropriate to this thread, it's a broader approach to pedal boat innovation, beyond engineering, just let me know if this kind of posts are not useful
     

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  9. portacruise
    Joined: Jun 2009
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    portacruise Senior Member

    See CAPS response above.

    Porta
     
  10. Guest625101138

    Guest625101138 Previous Member

    Dennis
    I get range 2 of the wire specified on the linked page:
    http://www.onesteel.com/products.asp?action=showProduct&productID=134&categoryName=Wire Products

    I have used up to 10mm. It is surprising how low the shear stress is for the torque on shafts. Most prop shafts are sized on critical speed. If the shaft does not have a long unsupported length in air then critical speed does not come into consideration; at least for small diameter.

    I paint the shafts otherwise they rust. I have considered using the spring steel as the former for wrapping layers of glass tape and epoxy so the steel is protected from corrosion but never got this far. Paint lasts a few years if you treat the shaft carefully. I store them under cover. I have a quick, no tools connector so I can remove them for transport. It also overcomes the problem of the prop spinning in the wind as I drive.

    The spring steel is very tough and hard. It can be bent at tight radius. It is almost impossible to drill. I have managed to cut a partial thread but I destroyed the die. I have devised different methods for clamping. The easiest is to grind a flat and tighten a grub screw on it. The torque is rarely a constraint for me. It is the torsional stiffness so having a connection that creates a torsional stress raiser is not a problem. There are a couple of ways to connect to avoid a stress raiser.
     
  11. Guest625101138

    Guest625101138 Previous Member

    Beppe
    A lot of water under a few keels since you were last here.

    If you have a few hours scroll through this thread:
    http://www.boatdesign.net/forums/boat-design/dare-say-no-30261.html

    It will give you some insight into why pedal boats are not available in large number. My conclusions are:

    The boats are quirky. So until there are a lot of them in use they will remain so.

    Boat designers see them as beneath them. They still want to design and build boats that have 1000+HP engines. Hence the pedal boat builders are essentially amateurs.

    The Hobie sets the current standard in pedal boats. They are rubbish from a performance point of view. Most people do not realise it until they compare the Hobie with something else - even a good kayak. My sister took the linked video from her Hobie:
    http://www.boatdesign.net/gallery/data/500/Hobie_view_of_V14.AVI
    Problem is there are not enough other pedal boats operating to provide the visible comparison.
     
  12. beppe
    Joined: Jul 2008
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    beppe Junior Member

    Rick, a lot of water under our keels, indeed! - I have been studying a bit more of innovation 'science' since then, and while I can see you are overtly pessimistic (and I can see why!) I can suggest a few very good reasons pointing to a better future scenario for pedal powered boats:

    1.
    Technological innovation is not just technological, it's a complex socio-technical process. Innovative artifacts are often boosted by social groups completely different from those already intersted in the technology. A successfull pedal boat design will probabily NOT emerge from the extant boatbuilding industry. See what I mean from this example:

    "I live in *** where there is a very large population of bicyclists (…)
    We have a very warm season from April to September where it would seem to be very logical for bicyclists to be pedaling on Lake *** or *** Lake rather than on the highways here. (…) There are several of us here that would like to make these bikes available for the riders here. The concept of finding a manufacturer locally to reproduce the design is very feasible. Your idea of local parts makes very much sense. (…)"

    This is from an email received at The Open Waterbike Project; I omissed the references to the city (maybe you can guess) because I didn't asked for the permission of showing it in public forums, but the same applies for example to the Venetian lagoon (i meen Italy) or the bay of San Francisco and in general to evey concentration of people where there is an extension of reasonably calm water and possibly a number of commuters. So we have a social group (possibly two: cyclists; commuteres) potentially interested to pedal boats, mostly non-customers of the nautical industry.

    Several possible uses of pedal boats, some of them rather unexpected, are emerging through the project; it's from them that we can expect a boost, the tricky thing is how to identify them, connect with them and get the process started. But this is also possible.

    2.
    This is another interesting point. I agree with you Rick, I believe we discussed Mirage efficiency issue in a previous post on this thread.
    Here the interesting pattern (in innovation 'science' there are not engineering certainties, but there are consistent patterns...) is that EFFICIENCY MATTERS. New markets of technological artifacts DO select according to efficiency in the end; so the success of Mirage canoes is good news, because it can lead to the social acceptance of the idea of waterbiking while showing the superiority of different pedal boats in the due time to all those intersted.

    Final remarks: pedal boats are waiting for their moment. If this will really lead to the emergence of a new market is unpredictable, but there are good signs. History does NOT repeat itself, failures of the past can easily become successes in the future, because the surrounding conditions have subtly changed. Any moment now...

    Best
    Giuseppe
     
  13. MarkX
    Joined: Feb 2010
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    Location: Azores

    MarkX Junior Member

    Kayak anglers are probably the biggest new market for pedal boats.
    Not least because we would like to have our hands free to play fish while still being able to move.

    I must add I haven't actually tried it yet but am about to build an HPV boat. Got my 16"x16" APC model plane prop and am now trying to come up with the drive for it, about 6-1 ratio.

    Drive Choices:
    1) I think on the first prototype drive I will be using 2mm stainless steel cable. Providing it doesn't slip, this should be the simplest solution as the pulleys are easy to make. The main problem is the crimp join in the cable, it's weakest point. Because of this it's not possible to make the pulley grooves the optimal rounded shape for cable.

    2) Also thought about not having rotary pedals but having the pedals hang down like pendulums. They power transmission (and crank return) would again be via S/S cables onto one-way sprag bearings. A complicated way of doing things but the advantage is that one doesn't have to stick the leg in the air on the power stroke as with rotary pedals.

    3) Twisted toothed/timing belt/s. Would be nice to be able to do this with just the one belt but the 6-1 ratio means the belt does some major convoluting because of the size of the large pulley. It could be better to have a twisted belt between the prop and a pulley, then a normal bike chain setup doing the gearing between pulley and pedals.

    4) I have some rather nice 1-1 nylon bevel gears which would do for a vertical shaft from the prop. There still needs to be some convoluting after that though, so it's probably not very efficient.


    BTW. I think it should be possible to make one's own large timing belt pulleys of any size in GRP by using an actual belt as the mould.
     
  14. beppe
    Joined: Jul 2008
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    beppe Junior Member

    Porta
    you say sensible things and I would have completely agreed with you just a couple of years ago. Sometimes, thought, the history of technological innovation tells a different story and suggests therefore a different course of action:
    1.
    Well this doesn't seems to be the case; we know than there are actually a few manufacturers of pedal boats operating today. They have been building and selling all manners of pedal boats for a number of years, some of them fine crafts, some of them less so; some are still alive, so I believe they have been making profits an maybe someone still does.
    This is not unusual at all, I'd say it's a consistent pattern in the period preceding the emergence of a Dominant Design, in which a great diversity of artifacts is proposed to the market by several inventors and entrepreneurs, each of them very confident in his or her product. For example, believe it or not, Mr Karl Drais von Sauerbronn, the inventor of the draisenienne (see picture) started a successful business and sold a few of his machines to the German Post to equip postmen, an that was in the 1820s!
    Problem is, these firms operate in a very fragile business environment, they are exposed to sudden fading of the craze supporting their operation and often fail, sometimes destroying the lives of their creators, as was the case of der Freiherr of Drais and many many others.

    2.
    I enclose a picture I like very much, it's the brochure of the Sea Saber, one of the finest pedal boats ever built (circa 1970). As you can see the approach is lightweight and the boat seems really fine. Unluckily the destiny of the firm and of the boat followed the same pattern we saw before (I don't know the detals: does someone knows them?): "the path towards a new dominant design is littered by the corpses of promising start-up firms too numerous to count” as Geroski poetically described it...

    It's impossible to predict the imminent emergence of a new dominant design, but there are reasons to believe that this could be the case for pedal boats now. For several reasons (but essentially because the design is intrinsically less performant and this matters) I don't believe that it will be based on the Hobie Mirage concept; I woudn't be surprised, on the contrary, if the flexible shaft drive system (it seems to me that it was independently developed in different forms by Mark Drela and his colleagues at MIT and by Rick Willoughby) will be one of the key components. It could be the necessary breakthrough. We'll see...

    Best
    Beppe
     

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  15. portacruise
    Joined: Jun 2009
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    portacruise Senior Member

    Porta
     
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