paddlewheel

Discussion in 'Surface Drives' started by rasorinc, Dec 13, 2008.

  1. rasorinc
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    rasorinc Senior Member

    Is there such a thing as a more efficient paddlewheel? How about shape--rather than a flat wood board? spoon shape?? cupped shape?? thanks much.
    Forgot, this will be a small application about 22".
     
  2. Guest625101138

    Guest625101138 Previous Member

    Think BIG. You need large diameter and wide wheel/s. THe objective is to have very low slip and this requires large blade area. However shallow immersion is more efficient than deep immersion.

    Think small with the arc of immersion. Less than 60 degrees is what I recommend for efficient operation.

    If you get the basics right then blade shape or blade articulation does not matter much. I would recommend a slight lead with the blades so they produce a net uplift rather than down force. The blades should exit the water cleanly without lifting any noticeable volume.

    The best size wheels will have some windage issues that you can be reduced by fairing around the wheel/s.

    I have posted performance predictor elsewhere but it needs to be adjusted to suit the boat. You can play with the size of the wheels to determine the power required for various combination of diameter and width.
     
  3. rasorinc
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    rasorinc Senior Member

    Paddlewheels

    Rick, thank you for your reply. I drew out a 20" circle and divided it into 60 degree radiuse's and came out with 6 paddles. Reducing to 52 degrees + or -
    I could get 7 paddles. Question-- if the paddles were, say, 18" x 6" out of steel and mounted on a steel ring all very strong could they turn at 3,500 RPM? And if so, could power and speed be an expected outcome?
    Thanks very much, and I know I'm over my head on this. Stan
     
  4. messabout
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    messabout Senior Member

    I'm over my head on this subject too. However I suspect that a paddle wheel turning at 3500 or anywhere near that speed, the result will be a lot of splashy foam and very little propulsion. Balance, too, will become problematic.

    Examination of the geometry of the wheel and its interface with the water, easily leads us to the conclusion that bigger is better. Lay out a path tracing of a single blade as it moves through the water. You will see that there is much down force and subsequent up force generated. All that is useless expenditure of energy. The force that you want to generate is in the horizontal plane. A big wheel is far more efficient in that regard, and a giant sized wheel is even more efficient.

    A wheel in the size that you are contemplating is better suited for mixing daquiris or margaritas for a large party.
     
  5. Guest625101138

    Guest625101138 Previous Member

    You need 12 paddles because you want to have at least ONE always in the water. With 6 combined with 60 degrees of immersion you will have a brief period with no paddle in the water.

    The speed of the wheel will depend on the speed of the boat. My initial impression was that you were making a 20" scale model boat. I did not relate the 20" to the size of the wheel. For a full size boat 20" is hopelessly small if you seek efficiency.

    The efficiency is primarily related to the slip of the paddles. The peripheral speed would ideally be 10% faster than the boat speed meaning the paddlewheel would be a bit less than 90% efficient. This usually results in a massive wheel relative to the boat. A wheel of practical proportions can usually give better than 75%.

    If you were to spin a 20" wheel at 3500rpm it would be an excellent fountain but not much value in driving a boat.

    If you provide some detail on the type of boat and target speed I will give you the wheel size required to get around 75% efficiency. I expect you will be surprised by how big it needs to be.
     
  6. rasorinc
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    rasorinc Senior Member

    Thanks very much for the input and your knowledge. I thought I might be chasing a wild hare and you just proved it. It might make a big blender.....
    I'll drop my idea now. Thanks again, Stan
     
  7. tom28571
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    tom28571 Senior Member

    Rick,

    You seem to know a lot about paddlewheels. Have there been any successful articulated paddles that had only vertical paddles? How about tip fences on the edges of paddles? I've spent a number of hours watching paddlewheels thrash through the water on a riverboat and wondered about these things.
     
  8. Guest625101138

    Guest625101138 Previous Member

    Tom
    I have not built a wheel but have looked at design information and validated it against various examples I have found and some basic test information from human powered wheels.

    If the wheels are sized correctly and positioned properly then things like blade shape and articulation have less benefit.

    There are certainly articulated paddles in operation and they are regarded as successful.

    THere is an array of paddlewheels shown in this video clip:
    http://www.youtube.com/watch?v=-QjRM-cQpHw
    If you look carefully you will see many examples and get an idea of the different performance. Even the best of the paddlewheelers has under sized wheels in my view. However it still performs well against the competition but I doubt that many of the boats have well engineered props. A good canoe could do 7km in about 35 minutes so none of these boats are very impressive.

    Look through the video a few times and pick out all the wheels. It is interesting to watch Hydrodynamosaurus at the start. You will see it kicks up a lot of water until it gathers speed and as the slip reduces there is less wasted power. A bigger wheel would cause even less spray. Also notice that the paddlewheel gives the best acceleration.
     
  9. boat fan
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    boat fan Senior Member

    I really enjoyed watching that .

    So Rick , in terms of total overall efficiency , how does a paddle wheeler compare with a conventional shaft / prop setup , in a power boat assuming both systems were configured optimal. Also assuming the same boat of course .By efficiency I primarily mean fuel consumption , power input , for a given arbitrary speed .
     
  10. Guest625101138

    Guest625101138 Previous Member

    Peak efficiency for either prop or paddlewheel is up around 90%. Realistically after allowing for windage of wheels or appendage drag on a prop they both end up more like 80%.

    Problem with paddlewheels is that they do not suit rough water applications.

    Problem with propeller is that it is not suited to shallow water or obstacle ridden water at least for efficient configuration.

    So the selection is really application specific. With good design either system can achieve high efficiency.
     
  11. boat fan
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    boat fan Senior Member

    Thank you Rick.

    80 % .....Quite impressive :)
     
  12. tom28571
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    tom28571 Senior Member

    Thanks Rick, a very interesting video.

    I do know that the maintenance on the paddlewheels was way beyond any propeller boat I have ever experienced. Having driven both, I find it difficult to believe that a paddlewheel can be as efficient as a propeller. A propeller can operate at its max efficiency all 360 degrees of rotation while a paddle wheel blade only reaches max thrust at one point, dead bottom center. The rest of the time it is immersed, it is fighting gravity and using energy to do it. A simple view, I'm sure, but it seems reasonable.
     
  13. Guest625101138

    Guest625101138 Previous Member

    The main point of the video was to show that a well designed paddlewheel will be as efficient as a prop. Hydrodynamosaurus has bettered many propeller driven boats.

    If the water is only 1ft deep you can get much more efficient operation with a large diameter, full width wheel on a moderate size river boat than having a small exposed prop or jet thruster working at very high velocity ratios. Also the first log that comes along will destroy the prop or decent chunck of weed will foul the jet inlet.

    Most current paddlewheels are sized for times of abundant fossil fuel so efficiency has not been a design priority.
     
  14. Ramius41
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    Ramius41 Junior Member


  15. Stumble
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    Stumble Senior Member

    Just curious what if any andvantage a tread instead of a wheel might be? Think something like a tank tread... I can see it would allow a lot more horisontle force to be applied with relatively low vertical force.
     
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