1 The criteria hereunder constitute an alternative to those of paragraphs 3.4.3.3 and 3.4.4.3 of the
Code for the Construction and Equipment of Mobile Offshore Drilling Units, 1989 (1989 MODU
Code). These criteria apply only to column-stabilized semisubmersible units which have buoyant
volumes contained in watertight upper-deck structure.
1.1 The righting lever curve after damage or flooding, as set out in paragraphs 3.5.10 and 3.4.4 of
the Code respectively, should, before the second intercept angle, reach a value of at least 2.5 m (see
figure below). At least 1.0 m of this righting lever should arise from enclosed watertight volumes
above watertight flats positioned at, or above, the lowest continuous deck.
1.2 The righting lever curve after damage or flooding, as set out in paragraphs 3.5.10 and 3.4.4 of
the Code respectively, should have a positive range of at least 10°degrees between the first and
second intercept.
1.3 For the purposes of calculating the righting lever curve, buoyancy may be assumed from all
spaces which are closed as described in 1.4 and 1.5 below. If the lower edge of any opening which
is not closed as required in 1.4 and 1.5 is submerged, then the corresponding space shall be
excluded from the buoyancy beyond the angle where this opening is submerged, but shall be
included up to the angle where this opening is submerged. Any such loss of buoyancy shall not
cause the righting lever to fall below 1.0 m above the wind lever curve within the range specified
in 1.2.
1.4 Any opening submerged before the angle at which the righting lever required in 1.1 is reached
should be fitted with a remotely operated watertight means of closure. Means of closure of a
self-activating type may also be accepted by the Administration.
1.5 Any opening submerged after the angle referred to in 1.4 is reached and within the range
specified in 1.2 should be fitted with means of closure as required in 1.4 or with easily operable
weathertight means of closure.