Vcg

Discussion in 'Stability' started by BTScow, Nov 12, 2007.

  1. BTScow
    Joined: Dec 2006
    Posts: 42
    Likes: 0, Points: 0, Legacy Rep: 10
    Location: Madison, WI

    BTScow Junior Member

    Ok,

    Can some one please either explain how to find the VCG of just a bare hull (no mechanics, systems, plumbing etc..) or point me to a book that explains it. For instance, in a perfectly rectangular barge that is deck over all with the same shell plate, evenly spaced scantlings etc. The VCG is in the middle of the barge. What is the methodology to finding that (beside emperical evidence). How do you find the VCG of non-traditional shapes .... like a boat for instance.

    Currently, I am wrestling with some explanations that fall somewhat short of bridging the gap between concrete understanding and theoretical banter. Example, to find the CGs of each section take half the half-girth, measure up from your base line and you have your vertical arms * station # = vertical moments. VCG = sum moments/ sum functions.

    This is all well and good on a wine shaped section or even a hard chined section. But, when applied to a box it doesn't work out so well. Is this because I am not measuring correctly or because I so daft I can't figure out the VCG is obviously in the middle of the box.

    Thank you in advance for any and all responses.

    BTScow
     
  2. Guillermo
    Joined: Mar 2005
    Posts: 3,644
    Likes: 185, Points: 63, Legacy Rep: 2247
    Location: Pontevedra, Spain

    Guillermo Ingeniero Naval

    You have to perform a detailed weight calculation, as you are doing, which is tedious but precise. There are also some rules of thumb, but are less accurate.

    You have to be careful about how you approach the splitting of weights to be sure you are getting an accurate result. You must not take too big curved parts, as that can lead to mistakes in their CG position. Ideally it should be an integration of differentially small parts.

    A boxed barge may not have the VCG in the 'middle', because the bottom reinforcement is usually stronger than the deck one.

    Cheers.
     
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