Stream lines of a container ship

Discussion in 'Hydrodynamics and Aerodynamics' started by Surfer Naval Architect, Nov 19, 2020.

  1. Surfer Naval Architect
    Joined: Feb 2018
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    Location: Amsterdam, The Netherlands

    Surfer Naval Architect Naval Architect

    Hi guys,

    What do you think about the wake flow of this container ship? I think that the position of the rudders are creating this weird wake flow which is going to increase the wave resistance and decrease the hull efficiency. Much better example the last picture (picture 3), where only one rudder is installed.

    Curious about your thoughts.

    Attached Files:

  2. bajansailor
    Joined: Oct 2007
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    bajansailor Marine Surveyor

    But surely the reduced resistance by having a single rudder has to be compared against the increased safety and manoeuverability of having twin screws and twin rudders?
  3. jehardiman
    Joined: Aug 2004
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    jehardiman Senior Member

    Nope, the single screw ship is not as big, so meh...Since Noah, ships need to get bigger to be more fuel doesn't matter if you spend 30% more fuel to carry 100% more cargo. And don't believe me;...just count the container rows x stacks across the transom to see how different in size these two ship are.
    bajansailor likes this.
  4. philSweet
    Joined: May 2008
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    Location: Beaufort, SC and H'ville, NC

    philSweet Senior Member

    The rudders are operating in the slipstream of the props. So the first thing to realize is that the mechanics don't adhere to the conventional ideas of wave drag that apply to free flow. Force sources in the flow (props) and their wake jets, have to be treated separately. The rudders are designed to convert swirl in the prop jet into thrust, and that conversion leaves traces on the surface.

    Twisted rudder for reducing fuel-oil consumption
    Twisted rudder for reducing fuel-oil consumption - ScienceDirect

    Study on Performance of Combined Energy Saving Devices For Container Ship by Experiments

    Rudders analyzed in the first article.

  5. Mr Efficiency
    Joined: Oct 2010
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    Mr Efficiency Senior Member

    So Phil, with these specialized rudders converting the rotational swirl into thrust, what would be the difference be in nett thrust, between that, and if there was no rudder there of any kind ? And if there is still a deficit from having the rudder there, why are rudders not made retractable, or semi-retractable, aside from the mechanical complexities ? After all, these huge ships speed 99% of the time running straight, and do you need massive rudders to make what must be minor corrections ?
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