Formula for twin propellers calculation

Discussion in 'Props' started by Rodneyzhang, May 24, 2014.

  1. Rodneyzhang
    Joined: May 2014
    Posts: 4
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    Location: Auckland

    Rodneyzhang Student

    Hi, I'm a first year student in boat design and doing calculating for a propulsion system of a 13 meters boat. The project was set up with a twin engine, and I've already done power and shaft calculation which formulas were from Dave Gerr's book. Normally the Crouch's propeller method can be used for calculating a single prop. I'm trying to figure out the props size for this boat with specific pitch and diameter however, it was failed with Crouch's method. So, is there any formula or method that can do this job?

    Cheers
     
  2. DCockey
    Joined: Oct 2009
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    Location: Midcoast Maine

    DCockey Senior Member

    University student, Westlawn student or ??? How technical is your course?
     
  3. Ad Hoc
    Joined: Oct 2008
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    Location: Japan

    Ad Hoc Naval Architect

    If you have already calculated the engine power...it is then a simple matter of using the Bp-Delta charts.
     
  4. Rodneyzhang
    Joined: May 2014
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    Location: Auckland

    Rodneyzhang Student

    Hi David,

    It's Unitec New Zealand. The course is focus on power boats design in first year, then sail boats in last two years. You could find the introduction of my course which called bachelor of applied technology(marine) on www.unitec.ac.nz.

    Cheers
     
  5. Rodneyzhang
    Joined: May 2014
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    Location: Auckland

    Rodneyzhang Student

    Hi Ad,

    It's so helpful. Thank u very much!

    Rodney
     
  6. Mik the stick
    Joined: Dec 2012
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    Location: Devon

    Mik the stick Senior Member

    Rodney
    I'm pleased the BP charts will solve your problem. I have Gerrs book, and to use these charts you need the formulas that go with them. What I don't understand is you failed using the Crouch method. Using the Crouch method for prop sizing gives slightly different, less efficient results. If you are a student and this design has not been built and tested with the prop calculated using the crouch method, then how has this method failed.
     

  7. Rodneyzhang
    Joined: May 2014
    Posts: 4
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    Location: Auckland

    Rodneyzhang Student

    Hi Mik,
    Thank you for your reply, that was my misunderstood of Crouch method. You are right, finally I used both BP charts and Crouch method to solve it after talking to my tutor. As a student I want to learn more about calculation and design to wide my knowledge which could be useful for my future work.
    Cheers,

    Rodney
     
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