Thursday, 26 January 2017

Topic-5 SECTIONAL AREAS AND VERTICAL MOMENTS

One of the fundamental hull form characteristics required to prepare the hydrostatic curves are the immersed sectional areas at ordinate stations. The cross-sectional area of each ordinate station shown in the body plan up to the waterline in question is determined which is the input into the calculation of the volume of displacement; this set of curves is known as the Bonjean curves. A typical plot of the bonjean curves is as shown in figure below. When plotted against the ship length, the immersed areas at the ordinate stations form a sectional area curve, whose shape represents the fullness or fineness of the ship form, an important consideration in ship resistance and towing power.
The bonjean curves are used:
  • Bonjean curves are drawn on the profile of the vessel. With these curves, we can find the distribution of buoyancy for any waterline (any draft, any trim).
  • To find out the volume of displacement and LCB at a trimmed waterline at which the ship is floating due to distribution of cargo or when the ship is floating on even keel.
  • In subdivision of ships from the safety point of view so that when the ship is flooded due to accident or damaged, the ship does not sink beyond the margin line.
  • In launching calculations, to determine the buoyancy and centre of buoyancy.

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