Section 2 Stability Criterion under Wind Force

201. Intact condition

1. Righting moment curves and wind heeling moment curves related to the most critical axis, with supporting calculations, are to be prepared for a sufficient number of conditions covering the full range of drafts corresponding to afloat modes of operation.

2. Where drilling equipment is of the nature that it can be lowered and stowed, additional wind heel- ing moment and stability curves may be required, and such data is to clearly indicate the position of such equipment.

3. The righting moment curve is to comply with the following requirements depending on the type of unit. (See Fig 7.3)

Fig 7.1 Righting moment and heeling moment curves

(1) Column-stabilized unit

The area under the righting moment curve to the angle of downflooding (area : A+B) is not to be less than 30 % in excess of the area under the wind heeling moment curve (area : B+C) to same limiting angle.

(2) Units except column-stabilized unit

The area under the righting moment curve to the second intersection(ßĮ) or downflooding angle (ßĪ), whichever is less (area : A+B) is not to be less than 40 % in excess of the area under the wind heeling moment curve (area : A+B) to the same limiting angle.

(3) In all cases, the righting moment curve is to be positive over the entire range of angles from upright to the second intersection(ßĮ).

202. Wind heeling moment

1. The wind heeling moment is to be calculated at several angles of inclination for each mode of op- eration, based on the wind force obtained from Ch 4.

2. The calculations are to be performed in a manner to reflect the range of stability about the most critical axis.

3. The lever for the heeling force is to be taken vertically from the centre of lateral resistance or, if available, the centre of hydrodynamic pressure, of the underwater body to the centre of pressure of the areas subject to wind loading.

4. In calculating wind heeling moments for ship-shaped hulls, the curve may be assumed to vary as the cosine function of the vessel's heel.

203. Wind tunnel test

Wind heeling moments derived from authoritative wind tunnel tests on a representative model of

the unit may be considered as alternatives to the method given in 202. Such heeling moment termination is to include lift effects at various applicable heel angles, as well as drag effects.

de-

204. Other stability criteria

The stability may be reviewed and evaluated in accordance with the alternative criteria deemed ap- propriate by the Society, taking into account the operation modes and environment conditions.