What is Shaft power formular

Discussion in 'Boat Design' started by Adeyele, Aug 30, 2012.

  1. Adeyele
    Joined: Jun 2012
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    Adeyele Junior Member

    Dear all, pls can somebody help me out with a simplified formular for "Propeller Shaft Power".

    Looking forward to a reply?

    Regards
    Mike
     
  2. rasorinc
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    rasorinc Senior Member

    Not sure if this is what your looking for but shaft power is power at the prop. If you know the rated horse power then multiply by 7 to get shaft horse power.
     
  3. Adeyele
    Joined: Jun 2012
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    Adeyele Junior Member

    Yes! i mean shaft power formular or delivered power formular. i have a formular here that states: Shaft power =torque x 2pien. but am in thought of it. the torque=(Rho)Va^2 D^3 X Fq (ND/Va)

    in dis form. i dnt knw.
    Va=rate of adv,
    D=prop diameter.


    Any hlp is welcomed.
     
  4. jehardiman
    Joined: Aug 2004
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    jehardiman Senior Member

    Shaft Hp (shp) = QN/550 where Q is shaft torque in ft-lbs; N = rps (1/sec); 550 is the HP constant.

    Effective Hp (ehp) = T*Va/550 where T is the thrust in lbs, Va is the speed of advance in ft/sec.

    Q = Kq rho N^2 D^5 where Kq is the torque coefficient from the prop curves at the Advance Coefficient (J = Va/ND)

    T = Kt rho N^2 D^4 where Kt is the thrust coefficient from the prop curves at the Advance Coefficient (J)
     
    Last edited: Aug 31, 2012
  5. gonzo
    Joined: Aug 2002
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    gonzo Senior Member

    The power gets calculated the same whether it is at the propeller shaft, a crankshaft or any other. It is a function of torque and RPMs. Outboards are rated at shaft HP. If you have an inboard, the rule of thumb is that you have a 3% loss in the gears.
     
  6. Leo Lazauskas
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    Leo Lazauskas Senior Member

    Adeyele,
    You could also have a look at the excellent and improving ITTC dictionary.
    http://ittcwiki.org/

    There is a lot in the section on propellers.
    http://www.ittcwiki.org/doku.php/structured_dictionary:propeller
     
    Last edited: Aug 31, 2012

  7. jehardiman
    Joined: Aug 2004
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    jehardiman Senior Member

    Damme Leo;

    Now you made me notice a typo...last line should be...

    T = Kt rho N^2 D^4 where Kt is the thrust coefficient from the prop curves at the Advance Coefficient (J)
     
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