Section 27 in The Merchant Shipping (Prevention of Pollution by Oil from Ships) Rules, 2010
27. Intact Stability.
(1)Every oil tanker of five thousand tonnes deadweight and above delivered on or after 1st February, 2002, as defined in sub-rule (37) of rule 1A, shall comply with the intact stability criteria specified in clauses (a) and (b) of rule 27, as appropriate, for any operating draught under the worst possible conditions of cargo and ballast loading, consistent with good operational practice, including intermediate stages of liquid transfer operations and under all conditions, the ballast tanks shall be assumed slack.-.(a)In port, the initial metacentric height' GMo, corrected for the free surface measured at 0 degree heel, shall be not less than 0.l5metres;(b)At sea, the following criteria shall be applicable -(i)the area under the righting lever curve (GZ curve) shall be not less than 0.055 m.rad up to θ=30º angle of heel and not less than 0.09 m.rad up to θ 40º or other angle of flooding θf if this angle is less than 40º and additionally, the area under the righting lever curve (GZ curve) between the angles of heel of 30º and 40º or between 30º and θf if this angle is less than 40º shall be not less than 0.03 m.rad;[Note: θf is the angle of heel at which openings in the hull, superstructures or deck houses, which cannot be closed weathertight, immerse and in applying this criterion, small openings through which progressive flooding cannot take place need not be considered as open](ii)the righting lever GZ shall be at least 0.20 m at an a angle of heel equal to or greater than 30º: ,(iii)the maximum righting arm shall occur at an angle of heel preferably exceeding 30º but less than 25º(iv)the initial metacentric height GMo, corrected for free surface measured at 0º degree heel shall be not less than 0.l5m.(2)The requirements of sub-rule (1) shall be met through design measures and for combination carriers, simple supplementary operational procedures may be allowed.(3)Simple supplementary operational procedures for liquid transfer operations referred to in sub-rule (2) shall mean written procedures made available to the master which-(a)are approved by the Central Government;(b)indicate those cargo and ballast tanks, which may, under any specific condition of liquid transfer and possible range of cargo densities, be slack and still allow the stability criteria to be met and the slack tanks may vary during the liquid transfer operations and be of any combination provided they satisfy the criteria;(c)will be readily understandable to the officer-in-charge of liquid transfer operation;(d)provide for planned sequences of cargo/ballast transfer operations;(e)allow comparisons of attained and required stability using stability performance criteria in graphical or tabular form;(f)requires no extensive mathematical calculations by the officer-in-charge;(g)provide for corrective actions to be taken by the officer-in-charge in case of departure from recommended values and in case of emergency situation; and(h)are prominently displayed in the approved trim and stability booklet and at the cargo/ballast transfer control station and in any computer software by which stability calculations are performed.
