Why NOT Kort nozzles?

Discussion in 'Props' started by cthippo, Nov 8, 2010.

  1. cthippo
    Joined: Sep 2010
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    cthippo Senior Member

    What would be the disadvantage to using Kort nozzles on a displacement cruiser? How about circular prop guards?
     
  2. peter radclyffe
    Joined: Mar 2009
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    peter radclyffe Senior Member

    go for it, up to twice the grunt at low speeds & long term endowment protection
     
  3. gonzo
    Joined: Aug 2002
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    gonzo Senior Member

    If you want high thrust at low speed they are great.
     
  4. dcweed
    Joined: Aug 2010
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    dcweed Independent Designer

    The only disadvantages are cost, and a reduction in rate of turn if the nozzles are fixed. If they are steerable, then maneuvering is great, but cost goes up considerably more. Regards, Weed
     
  5. cthippo
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    cthippo Senior Member

    @Weed, Greetings fellow Ham'ster

    Is there any advantage to a circular prop shroud without the airfoil chape, aside from protecting the prop?
     
  6. baeckmo
    Joined: Jun 2009
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    baeckmo Hydrodynamics

    NO!!! Just disadvantage, since the longitudinal shape is important!
     
  7. apex1

    apex1 Guest

    There are no Kort nozzles in a size that would fit your Cat.

    And if there were any, I doubt you would like their price tag.

    Finally, there is no advantage having a Kort prop on a sailing boat. (the opposite)
     
  8. dcweed
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    dcweed Independent Designer

    Good day CT, hope you're enjoying the rain.
    Whoa...this is a sailboat? Huh. A carefully designed and installed tube is a little better than nothing for thrust (seen it done), and cheaper than a real nozzle. But neither would be worth it on a true sailboat. The added skin drag and turbulence would measurably diminish sailing ability. On a motorsailor, maybe...if, and only if, the majority of operating time was spent under power and you didn't care about sailing performance. W
     
  9. cthippo
    Joined: Sep 2010
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    cthippo Senior Member

    No, it's not a sailboat, but rather a 34' powerboat that is intended to be a pure displacement vessel.

    Beyond that though, I was interested in the question as a global one, rather for my specific application.

    Spent most of the day in Anacortes. Didn't rain, but the wind was nasty!
     
  10. mydauphin
    Joined: Apr 2007
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    mydauphin Senior Member

    A properly designed nozzle with right airfoil will help low end propulsion but is difficult to get right, and not cheap. A bad design and your dragging another appendage underwater that can break, cause resistance and generally cause problems. Like everything else the devil is in the details.
     

  11. MikeJohns
    Joined: Aug 2004
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    MikeJohns Senior Member

    The trade-off is a large amount of drag in return for more efficiency with a heavily loaded prop. Vessels like tugs & trawlers benefit only while towing. They are fitted for ice protection on some vessels. They are usually troublesome and often fatigue crack in service since they are prone to so much vibration.
     
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