natural ferequency

Discussion in 'Stability' started by saeedeh, Oct 31, 2007.

  1. saeedeh
    Joined: Oct 2007
    Posts: 13
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    Location: China

    saeedeh naval architecture

    hi guys
    how can I calculate ang get some info. about natural ferequency of planning boat?
    is it important item in design?after that I want to compare it with frequency of porpoising? is there any similar study?
    thanks before :)
     
    saeedeh, Oct 31, 2007
    #1
  2. Fanie
    Joined: Oct 2007
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    Location: Colonial "Sick Africa"

    Fanie Fanie

    As far as I know if your boat porpoises the motor trim angle is incorrect
     
    Fanie, Oct 31, 2007
    #2
  3. Frosty

    Frosty Previous Member

    Trim will sometimes correct it bit is not neccesarily the reason for it.
     
    Frosty, Oct 31, 2007
    #3
  4. powerabout
    Joined: Nov 2007
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    Location: Melbourne/Singapore/Italy

    powerabout Senior Member

    saeedeh


    The 2 are not related, it a force-drag-lift issue ( and hence speed related)and as the guys say trim can fix it more often on slow boats less often on faster boats say 50kts and over being fast.

    A boat that performs best in a slight chop may well porpoise in dead flat conditions.( drag goes up)

    Quite often a longitudinal weight transfer can also stop it. ( angle of attack change)

    Different styles of propellors can also stop or create porpoising, due to their bow or transom lifting properties.

    If your talking a shaft driven boat you lose the ability to alter drive trim but weight and prop are still avaliable.

    Cheers
    Powerabout
    (newbie)
     
    powerabout, Nov 5, 2007
    #4

  6. Guest625101138

    Guest625101138 Previous Member

    This planing hull calculator will indicate if the boat has a tendency to porpoise:
    http://illustrations.marin.ntnu.no/hydrodynamics/resistance/planing/index.html
    It is a function of many factors. Speed and longitudinal location of CoG are important factors. Moving weight forward does indeed reduce the tendency.

    Rick W.
     
    Guest625101138, Nov 6, 2007
    #5
    1 person likes this.
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