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Factors affecting the design of an efficient paddle wheel

  1. Sep 26, 2010 #1
    I'm a student undertaking a challenging physics project. My project is based on the Factors affecting design of an efficient paddle wheel.
    Until now the factors i could think about are:
    -Number of paddles
    -Size and shape of paddles
    -Rotation speed of paddles
    Since my object of study is paddle design, I have decided to keep the hull shape constant for all possible designs.
    After doing heavy research and study I have understood that the motion of a paddle wheel boat will obey the law of conservation of momentum. As the paddles push the water in the backward direction, the boat would be propelled forward as per the above law. An effecient paddle wheel would be one that translates into maximum forward motion for a perticular amount of energy spent.
    I would appreciate your inputs on
    1. Explanation on the physics aspect
    2. Constructing a experimental model
     
  2. jcsd
  3. Sep 30, 2010 #2

    berkeman

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    Staff: Mentor

    What paddle shapes have you found so far in your research? What have you found so far about the difference in efficiency between a paddle wheel and a propeller?
     
  4. Sep 30, 2010 #3
    Consider the diameter of the wheel.
     
  5. Sep 30, 2010 #4
    how much it is submerged underwater.

    hint: less submersion is more efficient but slower
     
  6. Sep 30, 2010 #5
    Why would this follow? The paddle wheel is only doing useful work when it is submerged. More submersion should be necessarily more efficient; this is one of the principle advantages of the (fully submerged) screw.

    It's no different than paddling a kayak manually. You maximize efficiency by submerging the entire paddle. Sure, submerging half the paddle lets you move the oar more quickly, but you move less mass, generating thrust less efficiently. Velocity is bad (wasted energy), momentum is good (pushes the boat forward).
     
  7. Oct 2, 2010 #6
    ''What paddle shapes have you found so far in your research? What have you found so far about the difference in efficiency between a paddle wheel and a propeller?''

    Actually my only aim is investigating factors affecting design of paddle wheel (to make it efficient) I will conduct all the experiments later, first i want to get all the physics theory and hypthesis in order.
    It is correct that the more you submerge the paddlewheel in water, it will become more efficient. Which i did not think of, so i would have to keep this factor constant, right? The material of the paddlewheel and paddles should also be same?
    Now i am confused, can anyone suggest me what should be my research question (it should ideally be narrow) Mine so far: Investigation of the factors affecting design of a good efficient paddle wheel, or should i investigate only one factor which will allow me to write atleast 4000 words.
    Also:
    Newton's Laws of Motion, namely his third law which essentially states that for every action (a) there is an equal and opposite reaction(r) . In this case the paddle wheel is (a) and movement of boat is (r). What other forces would act on the boat?
    Can anyone give me more physics behind this topic in terms of:
    rotational motion, angular speed, torque, etc.
    Will the angle or something come into play? (i am confused about this part)
     
    Last edited: Oct 2, 2010
  8. Oct 2, 2010 #7
    Well, with a flat paddle, as the water is pushed it is compressed and will tend to roll to the sides and away from, a flat paddle.
    A concave paddle will also compress the water, but tends to "hold" more water volume.
    Consider this "l" versus this ")" or this "]"
     
  9. Oct 2, 2010 #8

    rcgldr

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    Homework Helper

    The obvious case is if the paddle wheel is completely submerged, then it only generates a torque and no net linear force, since you have equal and opposing forces on the paddles opposite from each other on the wheel.

    For partial submersion, there's some ideal point where the paddles don't waste too much energy pusing water downwards at entry, and upwards at exit. Too little submersion and the paddles don't move enough water.

    A "V" shaped paddle would have an issue with slowing down a boat, not sure if it's more efficient in forrwards mode.
     
  10. Oct 4, 2010 #9
    Just trying to study the relationship between angular momentum and the linear momentum for the paddle wheel. Will all the angular momentum be transferred to linear momentum, can there be any equation linking it (specific ref. to the paddle wheel)
     
  11. Oct 5, 2010 #10
    All the angular momentum might not be transformed into linear momentum.

    Since you are studying efficiency of paddle wheel out of curiosity I would like to know how to work out the efficiency percentage of paddle wheel. In many boat design forums they mention the efficiency in terms of percentage. How to calculate this percentage.
     
  12. Oct 5, 2010 #11
    Can your paddle wheel have a shroud?
     
  13. Oct 5, 2010 #12
    I imagine it would be the usual output/input power, where power = F*V.
     
  14. Oct 5, 2010 #13
    Articulating blades?
     
  15. Oct 5, 2010 #14
    So if we want to calculate input power do we derive force value from torque. Also what velocity do we consider. Should it be velocity with which water is pushed back.
    I hope someone clarifies this power and efficiency calculation.
     
  16. Oct 6, 2010 #15
    I dont think having a shroud will help. It will make the project even more complicated. It would be better to stick to calculations of power.
     
  17. Oct 6, 2010 #16

    sophiecentaur

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    Science Advisor
    Gold Member
    2017 Award

    The difference is that, with just one kayak paddle, you waste time getting back to the beginning of your stroke. With a wheel, you can arrange to have at least one paddle in the water all the time. And there would be a limit to the practical size of a kayak paddle.

    I could ask why it has to be a wheel. What about paddles mounted on a belt which dips into the water and then takes each paddle back along the whole length of the ship? Losses due to entry and exit would be reduced significantly. Never had those on the Mississippi, did they?
    Lots of maintenance problems though.
     
  18. Oct 9, 2010 #17
    Okay, so now i want to study one factor related to paddles in detail: no. of paddles, or shape of paddles or rpm of paddles. Which factor do you think i should study, which will allow me to give detailed argument and discussion on physics concepts
     
    Last edited: Oct 10, 2010
  19. Oct 15, 2010 #18

    berkeman

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    Staff: Mentor

    I would think that the number of paddles might be a good place to start.

    I forget if we covered this already, but an even better project would be to compare the efficiency of a paddlewheel to a propeller, given the same power input...
     
  20. Oct 15, 2010 #19
    Honestly I think you should study classical mechanics and fluid dynamics first, then you'll be able to solve the paddle wheel issue on your own.

    The benefit is that you can use your physics knowledge for the rest of your life as well as for this project.
     
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