Wake fraction and thrust deduction

Discussion in 'Props' started by Ogrim, Apr 12, 2017.

  1. Ogrim
    Joined: Jan 2013
    Posts: 10
    Likes: 1, Points: 3, Legacy Rep: 13
    Location: Southampton [UK]

    Ogrim Junior Member

    Hello,

    I am studying resistance in order to determine power and propeller for a 9m hard chine boat,
    here are results given by Wolfson power prediction program using stavinsky method:

    [​IMG]

    Im a bit surprised at the value of thrust deduction and wake fraction, that induced odd Va and thrust ...

    Could you tell me what you think about this table ? And what would be typical value for thrust deduction and wake fraction ?

    thanks =)
     
    Ogrim, Apr 12, 2017
    #1
  2. Ad Hoc
    Joined: Oct 2008
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    Location: Japan

    Ad Hoc Naval Architect

    It is impossible to comment without seeing the Lines the arrangement of the shafting and prop location in relation to the hull and its angle of inclination. There is no rule of thumb in that sense from an abstract!

    Those values look wrong too. How can you have the Va with a value of -60knots with a Vs of 20 knots??!!
     
    Ad Hoc, Apr 12, 2017
    #2
  3. sub_prop
    Joined: Jun 2012
    Posts: 5
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    Location: italy

    sub_prop Junior Member

    some other values look wrong, anyway assuming more reasonable values wt/100 and t/100 here the results
     

    Attached Files:

    sub_prop, Apr 27, 2017
    #3
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