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Propeller hydrodynamics

  1. Sep 9, 2007 #1
    hey guys,

    urgently need your help, im an industrial design student and at present we have a project that involves designing and constructing a peddel powered water craft. there will be a race upon completion of the craft therefore it needs to be reasonably fast.

    If you have any recommendations or suggestions please feel free to respond. The ideal feed back i would like to receive is regarding the most appropriate propellar to use, including draft and angles etc, and whether there is a more efficent solution out, as this craft will be manually operated in a similar manner to a bicycle.

    appreciate it guys

  2. jcsd
  3. Sep 10, 2007 #2


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    No magic formulas here, but some things to think about:

    You might want to start by estimating the max speed your boat is likely to have (which depends mainly on its length). Google for "Froude number".

    Then consider how much power your pedallers can generate using something that works like a bicycle for a sustained period of time (Google for power output of athletes for example).

    Choose a sensible pedalling speed (and possibly a gear system to convert that to propellor RPM).

    Then design a prop that works your chosen input flow velocity and does the right amount of work.

    Then have fun working out what went wrong with the design calculations when you test it (that's where the REAL engineering starts!)

    Of course if it's a very short race you may be more concerned about acceleration from a standing start than about top speed.

    You might want to consider paddle wheels rather than propellors. They could be easier to design (conservation of momentum!) and construct.
    Last edited: Sep 10, 2007
  4. Sep 10, 2007 #3


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    Check out Nature volume 424, there's an article (which is also on the cover page) concerning delta shaped paddles.
  5. Sep 10, 2007 #4


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    I would also recommend that you spend some time to look at the items that are readily available. It would be a big plus (and usually a lot easier on you) to be able to use items already manufactured and easily obtainable. You should also be able to get a lot of engineering data about those products if you ask the right people.
  6. Sep 10, 2007 #5


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    If you're involved in the competition I've seen on TV before, these are not surface vessels you're talking about. I've always hoped someone would try applying the principles of supercavitation to one of these races. Not that a human-powered craft could truly supercavitate, but if the driver's exhaled air could be trapped in long bubbles that cover much of the side of the craft, contact with the water could be greatly reduced.
  7. Sep 10, 2007 #6
    Thanks alot for the help guys, at present we are looking into the concept of flippers and possibly try and branch off into a less conventional approach, just to see what happens. gratefull for all the recomendations they help alot. its just a minor competion that we are in, just in new zealand.

    thanks again guys and feel free to keep ideas coming

    will keep u guys posted with our success...or lack of
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