prop whip

Discussion in 'Boat Design' started by gentleman, May 17, 2012.

  1. gentleman
    Joined: Oct 2011
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    gentleman Junior Member

    any body have any thoughts on prop whip? 7ft shaft with a 16/21 prop, is there a rule of thumb is to how far you can have a prop from a strut before prop whip occurs.....thank's.
     
  2. Petros
    Joined: Oct 2007
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    Petros Senior Member

    That seems to me it would depend on shaft diameter and material, rpm and hp. It is a function of shaft flex, and it is not only length, but load and stiffness as well. Harmonics may also affect it too. I do not know any details about boat applications, but I have studied it for both aircraft props and automobile drive shafts. In variably one or another car or truck manufacturer will try and save weight and cost on a rear wheel drive vehicles by eliminating the center drive shaft bearing and one u-joint. It will always results in more vibrations, and the need for a much stiffer (larger dia) shaft.

    It is a complex issue to calculate, but I am sure there have been some kind of "rules of thumb" developed from observations of propeller shafts over the years.

    Needless to say, the stiffer the shaft, the less issue you will have with it. The stiffness is a function of shaft diameter, shaft material, length to supports.
     
  3. Submarine Tom

    Submarine Tom Previous Member

    The only thing that comes to my mind is the long boats in Thailand!

    Why do you ask?
     
  4. gentleman
    Joined: Oct 2011
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    gentleman Junior Member

    the shaft i 1 and 1/4 inches in dia..
     

  5. keysdisease
    Joined: Mar 2006
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    Location: South Florida USA

    keysdisease Senior Member

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