Lackenby method

Discussion in 'Boat Design' started by Radenpm9, Aug 4, 2015.

  1. Radenpm9
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    Radenpm9 Junior Member

    [Ask] Lackenby method

    Hi all,

    I did boat modification by using Lackenby method. I moved every section from original position to new position in order to get new hull from parent hull. Even though I didn't move Aft and Fore perpendicular sections, to shift only LCB (longitudinal centre of buoyancy) position, value of Cp and Cb changed.
    Note: I calculate hydrostatic by using Maxsurf software.

    Did I miss some step?
    Have you got any thought?

    Regards,
    Raden PM
     
  2. Ad Hoc
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    Ad Hoc Naval Architect

  3. Radenpm9
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    Radenpm9 Junior Member

    Hi Ad Hoc, seems like no link provided to download that software. where can I download it?
     
  4. Ad Hoc
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    Ad Hoc Naval Architect

    The link is for you to confirm your own assumptions and methodology is correct. The software used in the link is most likely propriety to the university course in Japan.
     
  5. Radenpm9
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    Radenpm9 Junior Member

    oh okay, thank you very much. I will double check it.
     
  6. Radenpm9
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    Radenpm9 Junior Member

    I think my assumption and methodology are correct, but Cp and Cb still change
     
  7. LP
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    LP Flying Boatman

    Cp is based on midship section which is typically based on your largest section. This may have shifted using Lackenby and now your parameters are based on an erroneous section. :idea:
     
  8. Radenpm9
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    Radenpm9 Junior Member

    In my case, modification of yacht hull, my largest section area is not in the midship section. the largest section area slightly behind midship section.
     
    Last edited: Aug 8, 2015
  9. philSweet
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    philSweet Senior Member

    In the software FreeShip, a "Lackenby transform" is used specifically in order to change Cp.

    You enter you desired Cp and the transform iterates until the desired Cp is reached. So I think this is inherent in the method. Assuming this is the same method.

    Using a consistant reference point for calculating Cp and performing the transform is important. FreeShip operates on the user declared midsection in both cases.

    [Aside : In freeship, you can create lovely curved mast sections by importing a straight mast tube above a generic hull, rotating mast bow up about 45 degrees, and running Lackenby transforms, then saving the mast as a part again.This maybe gives a better visual indication of what the transform is actually doing.]
     

  10. Radenpm9
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    Radenpm9 Junior Member

    Thank you for your information Phil
    Just to confirm: do I need to move all of section except fore and aft perpendicular?
    but when I change LCB position to, let say 3% to aft, new position of section 0.5 will be behind aft perpendicular section
     
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