3.3.1 The stability of a unit in each mode of
operation should meet the following criteria (see also figure 1):
-
.1 For surface and self-elevating units the area
under the righting moment curve to the second intercept or downflooding
angle, whichever is less, should be not less than 40 per cent in excess
of the area under the wind heeling moment curve to the same limiting
angle.
-
.2 For column stabilized units the area under
the righting moment curve to the angle of downflooding should be not
less than 30 per cent in excess of the area under the wind heeling
moment curve to the same limiting angle.
-
.3 The righting moment curve should be positive
over the entire range of angles from upright to the second intercept.
Figure 1 Righting moment and heeling moment curves
3.3.2 Each unit should be capable of attaining
a severe storm condition in a period of time consistent with the meteorological
conditions. The procedures recommended and the approximate length
of time required, considering both operating conditions and transit
conditions, should be contained in the Operating Manual.
3.3.3 Alternative stability criteria may be considered
by the Administration provided an equivalent level of safety is maintained,
for example, criteria based on wind tunnel tests and behaviour tests
of a representative model in waves.