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Bonjean Curves

  • Curve plotted on lines plan of ship is calls bonjean curve, here the longitudinal section of the vessel is divided in 10 stations.
  • At each station transverse section and each draft, we calculate e area and moment of area., these moments then plotted on the lines plan....
  • Use: fo calculation of hydrostatics like displacement block coefficient centre of floatation TPC etc.
  • Enable the users to calculate the displacement and the centre of buoyancy for a given waterline, in an upright condition
  • curves of areas of transverse sections and their moments about the baseline of a ship used in making calculations (as to determine the force of buoyancy during launching)
  • The Bonjean curve had as its ordinate the cross sectional area at that section, up to the waterline concerned. Each curve was usually plotted with its axis The vertical axis was traditionally at ship scale.
  • Their main uses were for launching (end launching) and longitudinal strength.
  • For launching, prior to stern lift, the progressive waterlines would be set up on the ship profile with the Bonjean curves.
  • Where this waterline cut the vertical axis was the local draft at that section. Bonjean area was read at each such intersection, and then integrated longitudinally for both volume and moment.
  • These gave the volume of buoyancy and its longitudinal moment about the fore poppet for each successive waterline, to match against moment of weight force about the fore poppet, defining the point of stern lift.


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