Where to start on a pedal powered boat?

Discussion in 'Boat Design' started by ryan808, Aug 4, 2008.

  1. Guest625101138

    Guest625101138 Previous Member

    Been done before at least on a bike:
    http://www.classicrendezvous.com/images/bike shops/First_Flight/Alenax_closeup.JPG

    It is not as neat as roller clutches and you get a slight snap when the pawl engages whereas the roller clutches engage immediately.

    I think by the time you do the engineering to mount the sprockets and reeve the chain plus cords you may as well invest in a couple of roller clutches and a good hard shaft.

    Rick W.
     
  2. alan white
    Joined: Mar 2007
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    alan white Senior Member

    How much do those gear boxes cost?
    BTW, I'd always thought that spiral cut gears, because of a lateral sliding contact, were smoother but not as low-friction as straight-cut bevel gears.
    It was always true of parallel gears. The advantage, I thought, was smoother (hence quieter) meshing (the reverse gears of a car whine. They aren't helical cut because they aren't used much anyway, and they're cheaper than helical-cut gears.)
    I would have imagined that spiral-cut gears were no better than 90% efficient. But I've been out of it for a while, so I'm sure you are correct.
    There is a way to turn 90 degrees with no gears if the ratio is 1:1. It uses bearings and cranks and a third control element. Super-low friction.
    I like the twisted belt best of all. I've always banked on belt technology as the way to go. Look at the Subaru Justy with its belt drive tranny. Still gets amazing mileage.
    Also, is the propeller the most efficient push mechanism? i've got a fishtail device that works well in air. I wonder how it would do in water?

    Alan
     
  3. clmanges
    Joined: Jul 2008
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    clmanges Senior Member

    FYI . . . there are some one-way clutches that have a sprocket incorporated -- and they work with standard keyed shafting; no need for a hardened shaft.
    Here:

    http://www.daytonsuperiorproducts.c...id=googleppc&gclid=CPr5ttrGkZUCFQ4RnQodv3d-gQ
     
  4. Guest625101138

    Guest625101138 Previous Member

    Price - Earlier links to Mitrpak and McMaster sites provide prices.

    Efficiency - data has been measured and agrees closely with manufacturer's claim of 97% with seals run in at light to moderate loads. I am supposing the spiral faces allows smaller gears teeth and shaft while maintaining gear life which give the highest overall package efficiency.

    Belts - Toothed belts are no doubt good. Nauticraft do things reasonably well - a nice product with no outlandish claims. Gearboxes allow you to go to a completely enclosed design per attached image - box with 3.3:1 ratio. Add cranks and prop shaft - nothing simpler. The box shown cost USD150 and Ian Cassell got one as well but not sure if there are any left. They were made for the Wavebike and that project did not achieve commercial success so a limited run of boxes was available from Involute.

    Fishtail - Possibly the simplest to engineer but has some limitations. Must operate submerged to be efficient. I found vertical oscillation the best. Hobie have the best engineered system I have seen and it gives around 38% efficiency at typical cruising effort. My foil was up around 80% efficiency at 8kph but clumsy compared with the Hobie system. Theoretical efficiency is up at 90%. Props are the best efficiency over the widest range of applications.

    I started a Pedal Powered Boat thread that has already gone over the points raised in this thread:
    http://boatdesign.net/forums/showthread.php?t=23345

    I am still looking for the perfect propulsion system. It is hard to better a paddle for human power.

    Rick W.
     

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  5. johnnyld_3
    Joined: Jul 2008
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    johnnyld_3 New Member


    If you borrow Rick Willoughby's 1/4" spring steel prop shaft idea, everything can be done in the boat, or off to the side...above water, simplifying the design.

    He talks about the shaft in this thread, has pictures and a video. Very good idea. It is an unbelievable concept grasp until you watch it action.

    http://www.boatdesign.net/forums/showthread.php?t=23345
     

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  6. alexlebrit
    Joined: Aug 2006
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    alexlebrit Senior Member

    You wouldn't actually need that middle chain-cable-chain section, you could easily use a single piece of chain and loop it over a deraillieur jockey wheel , mounted on the same axis as the two sprockets.

    I think there's good reasons to look at using standard bike components and you mentioned it in your post - junk bikes - while I'm sure many of the posted items are more efficient, or longer lasting, they're also quite expensive for what for many people will be a first PPB. We can all learn from people who've already built lots of boats, but if it's a first we might not want to put in that much investment, so anything we can scavenge is an added bonus.

    As for mounting these junk bike components, here's a couple of thoughts - first the ultra cheap version:

    A cheap single speed kids bike will usually have a freewheel/sprocket screwed onto the hub, and the hub is a simple tube with the spoke flanges welded on. Take two of these hubs and cut through the central tube section. Use a tubular prop shaft and slide these over it, drill through and bolt/rivet them on. Now thread the tube internally and bolt the prop on the other end.

    Now the slightly more expensive version:

    Take a sealed bottom bracket and get an adaptor machined. This should have the shamfered square hole to match the BB and the thread to match the sprockets. I don't imagine it'd be that costly to get made up, it'd just be a matter of knowing what thread to cut and I'm sure this must be available somewhere. The great advantage to this is that the sealed BB takes you from dry side to wet side with no leak worries.

    Just a couple of thoughts.
     
  7. Petros
    Joined: Oct 2007
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    Petros Senior Member

    strait cut gears are more efficient (less power loss) but not as smooth as the gears with helix. Not an important issue I would think with a humanpowered craft, high powered device will have annoying vibration, not so much with only .25-.35 hp from a human.

    a good prop design is way more efficient than paddle wheel or any fish tail device. A prop is a foil going in a circle around a shaft, the best ones would have high aspect ratio blades and would turn slow (power boat props have to have short blades because of the speed they run at). Make sure it is a good design however, some of the little props they put on electric outboards are junk. Look for an elliptical blade profile, high aspect ratio blade, contoured shape with varying angle of attack (slight twist in the blade) from root to tip. Not simple flat plates at angle to shaft.

    V-belt drives are not efficient, they have a lot of friction. That is the only kind of belt you can put a 90 deg twist in it. The best belt is a cog belt, that is what is used in the Justy trans (and as a cam timing belt in most smaller engines), but you can not put a twist in these.

    A light bicycle chain drive would be more efficient than a belt, but I do not think you can get a 90 deg twist in a chain. You might try it with a very worn out bicycle chain, because if you can get it to make a full 90 deg twist from crank to propeller shaft that would be both simple, cheap (from junk bike parts) and easy to make. You can even link two bike chains together and get a longer run to make the twist, you need a little chain tool to push out one of the pins in a link.
     
  8. Guest625101138

    Guest625101138 Previous Member

    This video might change your opinion on paddlewheels:
    http://www.youtube.com/watch?v=-QjRM-cQpHw

    Their development effectively stalled once propellers came on the scene. They offer advantage over propeller in calm shallow water conditions. Efficiency is similar to a propeller if properly designed for the application. They also offer high thrust capability for lower draft than a prop.

    Rick W.
     
  9. Petros
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    Petros Senior Member

    oh there are ways to make paddles wheels efficient, but they would be way more work to design, build and install. It would be heavier than a prop too. You can likely buy a pretty good plastic propeller for less then $10. Why bother?
     
  10. alan white
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    alan white Senior Member

    It is obvious that the fewer power transfer points, the more efficient the system. That means that a gearset that both corrects RPM (for prop speed) and turns a right angle is an ideal transfer dynamic.
    For example, I can easily show how one could turn a 90 degree corner with bearings alone, but I'm still stuck with the smae RPM.
    So I'm still up against the ratio correction. To accomplish both functions in one mechanism is the best solution.
    If what Rick's gearbox source says is true, there is a 3% loss while correcting both shaft direction and speed, and that's outstanding. 3% is next to nothing as a total system loss (recognizing that the prop is like the tire on the road---- it has it's own inherent limitations of efficiency).
    Thankfully, truly superb bicycle cranksets are (relatively) cheap and available
    So what's left?
    I for one would like to see past my feet. I think it ought to be possible to rig a crank to allow the pedals to move linearly, which ought to lower the feet at least a foot or so. This not only would improve vision, but also it would allow an enclosed body shape with substantially less windage.
    Such a mechanism ought to be very efficient (simplest is a pair of kiddie-car connecting rods). See how linear bearings are now on practically every chop saw. There're your pedal guides (though I'd rather see solid bronze guides which are low friction but require oiling).

    Alan
     
  11. Guest625101138

    Guest625101138 Previous Member

    Paddle wheels are easier to make than a prop drive. Two ply discs with blades require very little engineering skill and can be made light. No need for gearing and a simple roller bearing in pressed metal housing on each gunwale. The reason they find application is the ability to operate in shallow water and weedy locations.

    Props can suffer serious problems with weed and obstacles. Takes lots of design detail to overcome these weaknesses. These are significant factors in the ready acceptance of the Hobie mirage drive.

    As far as props go you get what you pay for. The plastic prop will work but you will pay more than $10 for a good one and high efficiency requires matching to the application. Takes me 4 hours of dedicated effort and about $10 of stainless steel to make a good prop. I spend another hour or two designing it.

    The best purchased prop I have came from Bolly:
    http://www.bolly.com.au/models/glasstwo.html
    It is made for boats and cost me AUD40 plus postage. It is now AUD60 plus postage. I was getting around 75% efficiency from it. With a bit of reshaping it would do better. On the other hand a well designed paddlewheel can get over 80% efficiency.

    Rick W.
     

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  12. Guest625101138

    Guest625101138 Previous Member

    Alan
    Take a close look at V12 pedal operation here:
    http://www.youtube.com/watch?v=PYoW3XjHRbw

    Low windage was one of its benefits. Extra weight, compared with others I have made, was a disadvantage. Also lack of reverse made cleaning weed impossible without stopping per photo in earlier post.

    Rick W.
     
  13. Guest625101138

    Guest625101138 Previous Member

    This provides an alternate view:
    http://www.automation.com/resources...stealth-helical-planetary-gearhead-technology

    I have only tried one straight gear set and it was not strong enough to last very long but for the time it did operate I could feel the tooth mesh. This is not the case with spiral cut gears. Most of the precision boxes use spral gears anyhow.

    Rick W.
     
  14. alan white
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    alan white Senior Member

    I'd like to play with linear pedal systems and see what I can come up with. Do you use the return stroke (pedal clip) or just push?
     

  15. Guest625101138

    Guest625101138 Previous Member

    Alan
    It is a sweet system for gentle to mildly aggressive pedalling.

    With the two pedal system that we engineered you could not pull back on the pedals because the wire would go slack and runs the risk of coming off guides and the rollers. In fact we linked the front side of both pedals with wire through a pulley that was attached to a spring to maintain tension in the aft pull wires. The need the spring if you use swing arms because the length changes slightly.

    I did biomechanical analysis and testing on the pedal system to arrive at the geometry. I found the best arrangement was with swing arms having top mounted pivot. This results in simple harmonic motion and is extremely easy at light power levels. It is around 2 times more biomechanically efficient at light load than cranking. Once you start to load up the rhythm tends to go out of it and you just notice the steady back pressure on the pedals. At light load there is a noticeable sweet spot that can be tuned by playing with length of swing arms and where the legs sit at rest. For me it was close to 60 swings per minute. I set up to stroke the wire 2ft and my feet moved roughly 60% of the distance. Design wire force was 100N.

    I made foot rests that held my feet in place but there was no band to lock my foot and risk reverse force.

    There are pictures of Warren's system at posts#73 and my test frame #75 here:
    http://www.boatdesign.net/forums/showthread.php?t=23345&page=5

    Post #42 on this thread has more detail on a rowing type system with the roller clutches.

    Rick W.
     
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