Trimming Table

Discussion in 'Stability' started by haran, Jan 25, 2008.

  1. haran
    Joined: Jan 2008
    Posts: 1
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    Location: australia

    haran New Member

    Hello to all

    I am intrested to know how to create trimming table which given in the hydrostatic book. in details when we trim the ship for required draft we extract from the trimming table for appropriate hold then apply that to trimming quanitity.
    did anyone can explain how to create this table. I am not a naval architect.
    I worked onboard ship as chief mate.
    appreciate your help.
    rgds
    haran
     
  2. jehardiman
    Joined: Aug 2004
    Posts: 2,479
    Likes: 199, Points: 63, Legacy Rep: 2040
    Location: Port Orchard, Washington, USA

    jehardiman Senior Member

    You need to have or work up the Displacement & Other Curves (the "D&Os"). This will have the Moment to Trim 1 in/cm and Tons per inch/cm sinkage curves for any draft. Knowing these two curves and the inboard tank/hold arrangement and capacity curves, a Moment Diagram can be worked out. This drawing shows how much moment can be generated by adding weight to a particular hold/tank or shifting weight between two holds/tanks.

    In the design office, changes in trim are usually done graphically on the D&Os and capacity curves for an exact solution, but now many ships have custom spreadsheets/tabular data or loading programs that works out the approximate (usually so close you won't notice for most normal trims) changes needed affect a desired trim.

    For extreme trims or damaged calculations, the assumed "Normal" moment to trim and sinkage are too limiting and the moment to trim and sinkage are calculated directly from the lines and Bonjean curves.

    See this page for the equations. The table is just a lot of these simple equations solved for known hold/tank locations.

    http://www.m-i-link.com/outstation/formulatrim.asp

    Edit to add; Usually there is also a nominal check to the BG , KN, and GM curves also to prevent some weird combination of loading and ballasting from reducing transverse stability to nil and capsizing the ship. But as several recient accidents show, not all dangerous conditions get caught by the people who develop the tables.
     
    Last edited: Jan 25, 2008
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