1.2.1 The stability of a unit in the survival mode of operation should meet the following criteria :
.1 Capsize criteriaThese criteria are based on the wind heeling moment and righting moment curves
calculated as shown in section 3.2 of the 1989 MODU Code at the survival draught. The
reserve energy area 'B' must be greater than 10% of the dynamic response area 'A' as
shown in figure 1.1.
Area 'B'/Area 'A' > 0.10
Where:
Area 'A' is the area under the righting arm curve measured from
θ to (
θ 1+ 1. 15
θ dyn)
Area 'B' is the area under the righting arm curve measured from (
θ 1+ 1. 15
θ dyn ) to
θ 2θ 1 is the first intercept with the 100 knot wind moment curve
θ 2 is the second intercept with the 100 knot wind moment curve
θ dyn is the dynamic response angle due to waves and fluctuating wind
θ dyn = ( 10. 3 + 17. 8
C ) / ( 1 +
GM / ( 1. 46 + + 0. 28
BM ) )
C= ( L
ptn5/3 × VCP
w1 × A
w × V
p × V
c1/3 )/ ( l
wp5/3 × V
t )
Parameters used in the above equations are defined in paragraph 1.3.
.2 Downflooding criteriaThese criteria are bases on the physical dimensions of the unit and the relative motion of
the unit about a static inclination due to a 75 knot wind measured at the survival draught.
The initial downfloodlng distance (DFDo) must be greater than the reduction in
downflooding distance at the survival draught as shown in figure 1.2.
DF D
0 - RDF D > 0. 0
Where:
DF D0 | = | initial downflooding distance to Dm in metres |
RDF D | = | reduction in downflooding distance in metres |
| = | SF ( k × QSD1+ W ) |
SF | = | 1.10, which is a safety factor to account for uncertainties in the analysis, such as non-linear effects. |
k(correlation factor) | = | 0. 55+ 0. 08( a - 4. 0 ) + 0. 056 ( 1. 52 - GM ) |
a | = | ( F BD0 / Dm ) ( S ptn L ccc ) / A w p |
| | (a cannot be taken to be less than 4.0) |
| | (GM cannot be taken to be greater than 2.44 m) |
QSD1 | = | DF D0 - Quasi-Static downflooding distance at θ 1, in metres, but not to be taken less than 3.0 m. |
RMW | = | Relative motion due to waves about O1, in metres |
| = | 9. 3 + 0. 11 ( X - 12. 19 ) |
X | = | Dm ( V t / V p ) ( A wp2 / l wp ) ( L ccc / L ptn ) |
| | ( X cannot be taken to be less than 12.19 m ) |
The parameters used in the above equations are defined in paragraph 1.3.