natural ferequency

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

  1. saeedeh
    Joined: Oct 2007
    Posts: 13
    Likes: 0, Points: 0, Legacy Rep: 10
    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 :)
     
  2. Fanie
    Joined: Oct 2007
    Posts: 4,603
    Likes: 170, Points: 63, Legacy Rep: 2484
    Location: Colonial "Sick Africa"

    Fanie Fanie

    As far as I know if your boat porpoises the motor trim angle is incorrect
     
  3. Frosty

    Frosty Previous Member

    Trim will sometimes correct it bit is not neccesarily the reason for it.
     
  4. powerabout
    Joined: Nov 2007
    Posts: 2,902
    Likes: 61, Points: 48, Legacy Rep: 719
    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)
     

  5. 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.
     
    1 person likes this.
Loading...
Similar Threads
  1. urisvan
    Replies:
    21
    Views:
    4,467
Forum posts represent the experience, opinion, and view of individual users. Boat Design Net does not necessarily endorse nor share the view of each individual post.
When making potentially dangerous or financial decisions, always employ and consult appropriate professionals. Your circumstances or experience may be different.