Section 25(3) in The Merchant Shipping (Prevention of Pollution by Oil from Ships) Rules, 2010
(3)(a)Credit shall only be given in respect of double bottom tanks, which are either empty or carrying clean water when cargo is carried in the tanks above.(b)Where the double bottom does not extend for the full length and width of the tank involved, the double bottom is considered non-existent and the volume of the tanks above the area of the bottom damage shall be included in formula (II) even if the tank is not considered breached because of the installation of such a partial double bottom.(c)Suction wells may be neglected in the determination of the value hi provided such wells are not excessive in area and extend below the tank for a minimum distance and in no case more than half the height of the double bottom and if the depth of such a well exceeds half the height of the double bottom, hi shall be taken equal to the double bottom height minus the well height.(d)Piping serving such wells if installed within the double bottom shall be fitted with valves or other closing arrangements located at the point of connection to the tank served to prevent oil outflow in the event of damage to the piping. Such piping shall be installed as high from the bottom shell as possible and these valves shall be kept closed at sea at any time when the tank contains oil cargo, except that they maybe opened only for cargo transfer needed for the purpose of trimming of the ship.
