Tuesday, June 23, 2020

Angle of loll

  • Intial unstable ship will not be upright. While heeling one side, the angle at which the G & B coincides in neutral equilibrium.
  • If GZ=0 then angle of Equilibrium = angle of loll
How to Recognize
  • Vessel will not remain upright and will assume a list to either port or starboard.
  • Vessel "flops" to port or starboard.
  • Vessel will have a very long, slow roll period about the angle of list.
  • A small GM is known to exist, plus any of the above.
Angle of Loll
  • -ve GM
  • Unstable Equilibrium.
  • G on the Centreline.
  • Corrected by lowering G below M
CORRECTION OF ANGLE OF LOLL
  • Moving cargo to a lower position;
  • Jettisoning top-weight (in an emergency);
  • Reducing FSE by pressing up/emptying tanks;
  • Filling low ballast spaces such as DB tanks
  • Top up tanks that are already slack.
  • Start with the smallest tank on the LOW side first. (If a tank on the high side is filled first, the ship will start to right herself but will then tend to roll over suddenly in an uncontrolled fashion as she passes through the upright. She will then „whip‟ through to a larger angle of loll on the other side. She may even capsize if the momentum gathered is sufficient.) When the low side is filled first, the angle of list will increase initially, but in a slow and controlled fashion. After some time, the weight of the ballast water added will be sufficient to lower the ship’s COG (despite the extra FSE), to cause the angle of list to decrease. By this method the inclining motions of the v/l take place in a gradual and controlled manner
  • Now fill the opposite tank on the high side.
  • Fill tanks alternately, low side first, until the v/l returns to positive GM.
  • Ensure that all tanks are completely filled.

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