Friday, January 3, 2020

Angle of loll and Corrective action

Angle of loll

  • It is the state of a ship that is unstable when upright and therefore takes on an angle of heel either to port or starboard.
  • Angle at which a ship with initial negative metacentre height will lie at rest in still water.
  • If the ship in further inclined to an angle greater than the angle of loll , then the sip will capsize.
  • An initially unstable ship heels to certain angle and ends up in neutral stability.This angle is called angle of loll.
  • At angle of lool , GM=0 or KG=KM

Corrective action

  • First check if the vessel is listed or lolled.
  • Always presume it is loll for safety and work accordingly.
  • Calculate the volume of all tanks , check for any slack tanks.
  • In a listed condition , always try to lower the CG by discharging the high side of the ballast first.
  • Start filling the low side of the tanks( prefer small tanks to minimize the free surface effect during filling . Because if we fill the other side of the tank , the listing moment will be enough the capsize the ship
  • Gradually start filling the mid tank and then the other side tank.
  • Now the ship should be upright .If not try ballasting the other tanks in the same method
  • During loll, never ballast the high side of the tank because the ship's listing moment to the other side is enough for it to capsize

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