Why is the added weight method seldom used?

Discussion in 'Stability' started by xichyu, Apr 15, 2016.

  1. xichyu
    Joined: Apr 2016
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    Location: Dalian,Liaoning,China

    xichyu Junior Member

    Both the method of lost buoyancy and that of added weight yield the same draught, and the same initial righting moment. The displacements and the metacentric heights are different, but their products are the same.
    Nowadays the added weight method is seldom used (only for rough hand-made estimations).
    Why is the added weight method seldom used?
     
  2. Olav
    Joined: Dec 2003
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    Location: Filia pulchra Lubecæ

    Olav arch. nav.

    xychiu,

    admittedly I can only speak for myself, but this is the reason why I prefer "lost buoyancy" over "added weight":

    - It is quite easy to model the damaged compartment and leave out the hull skin for this - my hydrostatics software will do the rest, no need to determine the additional weight of the water in that compartment.

    - This is especially true when the compartment is not fully flooded, i.e. with the waterline below the upper boundary of said compartment. A similar case are waterjet tunnels that empty when the boat heels more than a certain amount.
     
  3. xichyu
    Joined: Apr 2016
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    xichyu Junior Member

    What hydrostatics software are you using?
     
  4. Olav
    Joined: Dec 2003
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    Location: Filia pulchra Lubecæ

    Olav arch. nav.

    RhinoMarine as a plugin for Rhino 4.0 SR 9.
     
  5. xichyu
    Joined: Apr 2016
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    Location: Dalian,Liaoning,China

    xichyu Junior Member

    Thanks!
     

  6. Rabah
    Joined: Mar 2014
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    Location: Bulgaria

    Rabah Senior Member

    Hello xichyu,
    It is not so reasonable to jump from one publication in another not replacing the subject!
    Error to think that added weight method is used seldom.
    On the contrary, very much often it is applied for compartments the first and second class, i.e. such which are not informed direct with overboard water through the breached /usually them fill in with ballast for alignment the heel and the trim/ or such which have message with overboard water but for which the upper edge of the tank is arranged below the levels of the damaged water-line /for example tanks in the double bottom/.
    But as outcome results in Diagram of statical stability Classification organization requires on other method /constant displacement/ then it is necessary to apply the formula:
    h2 = [(D+p) / D] *h1 - see post №22 from
    http://www.boatdesign.net/forums/stability/stability-damaged-ship-55460-2.html
    About the program Rhino Marine - to not cost to be engaged with him, he is very obsolete and cannot help you to calculate unsinkability. He does not have such functions. It is better to apply Maxsurf Stability, Russian Sea Hydro or Delftship Professional.
    _____________________
    NA Razmik Baharyan
     
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