Pedal Boat Design

Discussion in 'Boat Design' started by BG_Geno, May 28, 2006.

  1. tinhorn
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    tinhorn Senior Member

  2. clmanges
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    clmanges Senior Member

    oblique paddlewheel

    I was thinking about paddlewheels, and wondered why no one seems to have come up with this idea before: mount the drive shaft at an angle, and instead of having the wheel cage be cylindrical, make it conical.

    Advantages:
    * much lower profile for wind resistance
    * splash is thrown away from the boat, possibly making shroud unnecessary

    Disadvantages:
    * path of paddle blades is curved with respect to hull, losing some effectiveness
    * paddle assembly adds more overall width to boat
    * may require U-joint or other addition to transmission

    I put together a quick model of a four-bladed assembly to better visualize it. I am holding the driveshaft (a toothpick) in my fingers. The driveshaft angle for this would be 45 degrees.

    Please comment.
    Curtis
     

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  3. tinhorn
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    tinhorn Senior Member

    Dude, you're SO 1840s...
     

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  4. clmanges
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    clmanges Senior Member

    Thanks, Tinhorn. That first one really isn't much like mine; the second one is closer.

    Any time I get some idea that I think is new, I've learned to go look around before getting too excited about it.

    Still, I'd like to hear more about this idea. It does address a couple of issues (splash, and especially wind resistance) that I had with putting a paddlewheel drive on my rowboat. Would curved or twisted blades help?

    I think I may have another project here . . .

    Curtis
     
  5. BG_Geno
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    BG_Geno Senior Member

    Tinhorn, thanks for the link. There is certainly enough information there to reverse engineer a working version. Getting to see one in motion/action has raised another concern that I hadn't even considered though. You really can't just look at the wheels rotation/force efficiency as a fixed property. Not sure what the correct term is, but as your boat begins moving forward there would be slippage which really alters everything in relation to paddle angle.

    On a much larger many ton paddle wheeler this is not as big a concern of course, but on a small human powered pedal boat where optimum efficiency of the engine (stoker) is peddling at a fixed say 90 rpm, slippage might be a bigger issue. Food for thought.

    clmanges--Wow, what an interesting idea, and an especially clever/simple way to demonstrate it. I am not certain there would be a net loss in efficiency when balanced out with the paddle shape you chose because of the way it enters the water with the "pointy part" having a much smaller area which increases as the rotation puts more and more of the paddle into the water--the angle of the paddle in relation to forward motion. Any real losses would likely be in gearing those shafts at a 45.

    I wonder if the pointed paddle shape could be incorporated in a more traditional wheel?

    I almost had a shiver when I saw your pictures because I have always wondered how the human mind made the leap from a sort of obvious paddle wheels function to the less intuitive prop, and your image is sort of the missing link/bridge between the two.
     
  6. tinhorn
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    tinhorn Senior Member

    I've never seen angled sidewheels, but I've seen plenty of upright sidewheels on human-powered boats. (Well, pictures.) Seems to me that as long as you get adequate paddle area in the water, this wheel profile would work as well as upright wheels, and without the splashing and sail effect of sidewheel covers. Maybe even better, since the water contact area would be larger. Feathering (articulating) paddles would be a booger to design.

    Of the hundreds of old paddle wheel and human-powered boat patents I've seen, there are only a few using this angle concept. (There are also several really weird patents, including fully submerged wheels.) Screw props were being introduced about this time - I'm guessing that's why there wasn't further development of this concept.

    Good luck, and keep us posted!
     
  7. clmanges
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    clmanges Senior Member

    Yeah, at a fixed cadence and gearing, you're quickly going to reach some maximum speed, just as with any other propulsion system. Thrust balances against slippage and drag, and there you are. I think that's what's defined as 'cruising speed,' isn't it?
    The paddle shape I cut out was just a very crude preliminary demo, for my own visualization. I didn't take it further right then, because it was bedtime. Cut the ends off at some better angle to get more paddle entering the water, no problem.
    Curtis
     
  8. Village_Idiot
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    Village_Idiot Senior Member

    If you could mount the inclined paddlewheels so that you could vary the angle of attack in the water, then you could design the entire system around variable gearing to find the best efficiency for any given situation, load, etc. The person doing the pedaling could simply move a handle slightly to dip a little more paddle in the water. Combine that with a chain drive and 21-speed gearset and you have something approaching an infinite gearing/thrust arrangement (although I still think twisted belt would be less troublesome than twisted chain).

    Dual inclined paddlewheels would eliminate any problems with directional stability when inclined 180 degrees opposite to each other (or would that be 90 degrees?).
     
  9. clmanges
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    clmanges Senior Member

    I'm going to experiment with a small model, a little more refined version.
    And as to this:
    if you can get a chain to twist 90 degrees, you can get it to twist 45 even easier.
    More later,
    Curtis
     
  10. BG_Geno
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    BG_Geno Senior Member

    The prevailing "wisdom" in pedal powered boats from everything I have read is to gear for w/e your comfort zone is. Typically about 90 RPM. There are no gear sets etc as there are no terrain or elevation changes. The KISS or LIM mantra is also much more important because being stranded by a mechanical failure on the water is a bit more involved then on a bicycle lol.

    I have read through about 20 different design and build logs, some of them spanning 3-5 years and 3-4 revisions and everyone that starts out with complicated gearing systems etc. always ends up going to a single fixed set in the end.

    I do think the angled wheels Idea has a lot of merit and bears some thought. I also love the idea of a "feathering" wheel setup but every design I have modeled so far comes out pretty complex and overly heavy--even with CF connecting rods and pressed in UHMW bearing surfaces. I will keep tinkering though.
     
  11. Guest625101138

    Guest625101138 Previous Member

    BG
    I have only come across this thread since Michael Lampi replied to it.

    I have no idea if you have looked at this thread:
    http://boatdesign.net/forums/showthread.php?t=23345

    You might find some interesting aspects there.

    Some basics that you might be interested in.

    1. An optimised monohull will require 40% less power to do the same speed as an optimised catamaran. The monohull can be easily stabilised with outriggers mounted above the water level.

    2. You can make an efficient PPB propeller having a diameter around 8" and it can be mounted on a flexible spring steel shaft to jump over obstacles or lifted higher to operate in shallow water.

    3. I can provide a performance calculator for paddlewheel geometry based on any specific boat design. Generally people underestimate the size of the blades needed for efficient operation.

    4. PPB performance can be determined to within a few percent. Useful tools are JavaProp and Michlet. Godzilla is an optimising routine within Michlet that can optimise a boat underwater shape within set constraints.

    Rick W.
     
  12. clmanges
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    clmanges Senior Member

    V.I., I'm not sure what you mean about varying the angle of attack, but from what I understand about paddlewheels, it isn't something you want to do. A paddlewheel is not an airfoil, it's (usually) a flat board that you stick in the water and push. If you push it at any angle other than perpendicular, you waste power; it loses 'traction,' so to speak.

    You also don't want to change its depth in the water. The size of the paddle is chosen from a formula, and it needs full immersion to perform as designed.

    Finally, directional stability (aka 'tracking') has more to do with the boat's hull shape than it does with the chosen method of propulsion; you aren't going to cure a tracking problem by altering the orientation of its drive.

    Complicated gearing would be a total waste. The old steamers had a very limited range of speeds. Trying to drive one too fast would destroy the wheel, probably long before the engine ran out of torque.

    Go back and look at the link posted by Tinhorn; it has just about everything you need to know, including excerpts from an old engineering manual with the formulas and procedure for designing a paddlewheel. It does involve some math, but it isn't rocket science. Check it out.

    Curtis
     
  13. tinhorn
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    tinhorn Senior Member

    Feathering, or changing the angle of attack, was a big deal to the old-school paddlewheelers. They attempted several methods of having the floats (paddles) enter and exit the water as perpendicular as possible to the water's surface. To enter and exit at a steeper angle wasted energy and robbed the wheel of efficiency.

    It's late now, but I'll see if I can't compile some of the more intriguing ideas for feathering floats and post them tomorrow.
     
  14. Village_Idiot
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    Village_Idiot Senior Member

    I was thinking that by adjusting the angle of your tilted wheel, say between 30 degrees and 60 degrees, you could vary the thrust depending on load and operator conditons. Design of paddle may be important here - i.e., not just a straight plank, but perhaps rounded or some other shape.

    See above. I'm trying to think of ways to achieve optimum efficiency for different load conditions. What if you have a 250lb. operator vs. a 150lb operator? What if you are carrying two people vs. one person? What if you are carrying a load of cargo? If the paddlewheel is designed to be most efficient at a certain draft, then it needs to be adjustable as the boat will draft more or less. Same concept for calm vs. choppy surface conditions.

    Again, depending on design of blades, if they are cupped or angled in some way, they could put a latitudinal thrust on the vessel and possibly affect tracking. Even if they are designed to not have an angle, you would still get some degree of latitudinal thrust unless the axis of the wheel is EXACTLY perpendicular to the longitude of the vessel and there is no other slop in the engineering setup. I'm just saying... ;)

    True, most gearing is wasted on the water, as it is usually an uphill climb (from an automobile's perspective). However, I don't think we should ever give up on the idea. As technology and materials improve over time, maybe we'll be able to implement a relatively simple, robust variable transmission in boats one day (yes, I know that variable pitch propellers can be considered a 'variable' transmission, but they also have their issues). Anywayz, I was mostly just trying to think outside the box and doing a little brainstorming - a good way to go down the river is to recognize where the banks are...:p
     

  15. clmanges
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    clmanges Senior Member

    V.I., I don't know what kind of learning style works for you, but for me, I need some kinesthetic activity fairly early in the process, which is why I started on my simple paper model. Yesterday, I sat down at the drawing board and drafted up a six-bladed version of my idea.

    Looking at what I had drawn, I started to get a better understanding of what the wheel must do, and what it must not do. For instance, I thought at first that I might be able to make this thing quite small. After looking at the drawing, it began growing -- about fifty percent, so far -- not because I wanted it to, but because it had to in order to work. What I was discovering is that 'folding' a cylindrical wheel into a cone introduces a new set of constraints on the design -- and I've barely begun exploring this in depth.

    Try this yourself; you'll learn a lot.

    Some of your thinking above can be best looked at in terms of something like daylight savings time -- you can add something on one end, but you find out that you just lose it at the other end, and probably lose a little extra as well.

    Brainstorming is great, but it's only the beginning of a process. Bring out ideas thick and fast, good. But then, you have to examine each one methodically, and a lot of them will fail. That's good too; you learn what works and why.

    Now, since this is BG_Geno's thread, we might want to try to focus a little more on the specifics of his topic, but I'll leave that to him; he seems to be eager to absorb new ideas.
    Have fun,

    Curtis
     
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