Center of Gravity

Discussion in 'Stability' started by Bluwaterbrew, Oct 31, 2018.

  1. Bluwaterbrew
    Joined: Mar 2009
    Posts: 16
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    Location: North Carolina

    Bluwaterbrew Junior Member

    Sorry I have been MIA guys. Haven't had much time to work on the boat, I am dealing with a health issue too. Anyways, I think I figured out all of the calculations that I needed. I have attached some pictures of my progress.
     

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  2. Feridun Berk Akyol
    Joined: Jan 2019
    Posts: 5
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    Location: istanbul

    Feridun Berk Akyol Junior Member

    Well the 'In-service inclining test' is the most accurate way to determine the Center Of gravity.
    other than that you can easliy achieve KB and BM for your ship via stability calculations also your CAD software should help you about the calculation of CG(KG,Gm and GZ).

    to be more practical you dont realy need a GM calculation for such a 'river boat' but there is another practical way which is suitable for such a small boats which dont realy need to follow llyod rules or strict regulations. divide your hull into simple geometric shapes like prisms and do the math on paper.
     
  3. TANSL
    Joined: Sep 2011
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    Location: Spain

    TANSL Senior Member

    Frankly, I do not know if I understand what you are saying, but it seems to me that some concepts are not too familiar to you and you do not understand them. For example, to calculate the KB and the BM no stability calculation is necessary, you just have to calculate the hydrostatic values of the boat with the trim that you have at that moment. The KG calculation, on the other hand, is a more manual process in which there is little software, if any, that can calculate it (a spreadsheet will suffice).
     
  4. Feridun Berk Akyol
    Joined: Jan 2019
    Posts: 5
    Likes: 1, Points: 3
    Location: istanbul

    Feridun Berk Akyol Junior Member

    ı know its a manual procces. like ı have stated earlier 'In-service inclining test' is the most accurute way to determine CG. also ı do believe that the hydrostatic calculations and stability calculations are bound together from desing spiral standpoint.
     
  5. TANSL
    Joined: Sep 2011
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    Location: Spain

    TANSL Senior Member

    During the design process, definition of the ship, there is no other way to estimate the C. of G. than by estimating the weights and their positions on board. It is a process, let's call it "manual", which can be helped by tools such as a spreadsheet. When we talk about the "'In-service inclining test'" there is no "manual" way to do it; the whole procedure of the inclining test must be followed and it is not, at all, a "manual" process (it was many years ago but nowadays, fortunately, it is not).
    I believe that hydrostatics calculations and stability calculations are not bound together from any standpoint. Hydrostatics correspond to the boat in a static equilibrium position and stability tries to know how the boat behaves when it moves. Once the hydrostatics have been calculated, you can go around the design spiral a lot, before calculating the transverse stability curves.
     

  6. gonzo
    Joined: Aug 2002
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    Location: Milwaukee, WI

    gonzo Senior Member

    quote: "As I understand it the boat is trimmed properly when the CB and the CG line up vertically"

    The CG and CB always line up. Otherwise, the boat will rotate until they do. This only applies to a static boat. Since you are designing a planing hull, static conditions are not very relevant. You need to calculate dynamic lift to make sure the boat runs in proper trim when planing.
     
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