CHAPTER 4 FREEBOARD AND STABILITY

4200. Stability

Semi-submersible heavy lift carriers engaged in international voyage may be in accordance with the followings.

1. Stability requirements in transit condition

(1) 2008 IS Code Part A, Ch.2.2 and 2.3 apply. The windage area in loading conditions shall in- clude deck cargo.

(2) If the vessel's characteristics render compliance with 2008 IS Code Part A, Ch. 2.2 impracti- cable, then the criteria of Part B, Ch.2.4.5 may be used.

(3)

(4)

For intact stability the buoyancy provided by a part of large deck cargo such as semi-sub- mersible units, jack-up units, barges or ships may be taken into account, provided that the se-

curing arrangement is separately approved. The watertight integrity of the cargo is to be defined

and taken into account in the calculations. And the application of this requirement shall be au- thorized by Administration.

The damage stability standard shall be in accordance with SOLAS Ch.II-1 or ICLL 1966

Reg.27, including IACS UI LL65, as applicable.

(5) Ships with B reduced freeboard:

B-60 freeboard requires one-compartment damage, while B-100 requires two-compartment damage in accordance with Reg.27 of the ICLL 1966. The calculations are to be carried out assuming the damaged tanks empty and for representative loads, such as a semi-submersible unit and a

jack-up unit, as far as applicable. Damage extent is to be taken according to ICLL Reg. 27.

The buoyancy of the deck cargo not located within the damage extent for each damage case may be taken into account if authorized by Administration. In all cases, transverse extent of damage shall be taken from the ship’s side. And the SOLAS limit curve is considered in addi- tion as ships intended for the carriage of the deck cargo.

(6) Ships with B freeboard:

If, in addition to the SOLAS limit curves, it is desired to take the buoyancy of the deck cargo into account, calculations as for ICLL Reg. 27 corresponding to B-60 damage may be consid-

ered equivalent. And the application of this requirement shall be authorized by Administration.

2. Intact stability criteria in temporarily semi-submerged conditions

(1) The loading and unloading sequences are so planned that the stability is sufficient during all phases of the sequence. The buoyancy provided by a part of large deck cargo such as semi- submersible units, jack-up units, barges or ships may be taken into account.

(2) The GM at equilibrium shall not be less than 0.3 m. The positive range of the GZ curve shall be minimum 15° in conjunction with a height of not less than 0.1 m within this range. The maximum righting arm shall occur at an angle of heel not less than 7°. Unprotected openings shall not be immersed within this range. It may be required to calculate the stability about ad- ditional axis to determine the most onerous result.

(3) Whenever free liquid surface exists in a tank, the effect shall be considered. The calculations shall account for the real filling of the tanks, i.e., in particular the location of air pipes needs to be carefully considered. If the complete filling of the tanks is dependent on certain trim or

heel during the submerging sequence this needs to be clearly stated in the stability manual.

3. Damage stability in temporarily semi-submerged conditions

(1) The risks of accidental flooding of any one compartment on the ship shall be considered.

Damage to be considered is that which might occur following an uncontrolled movement of the deck cargo during loading or offloading leading to puncture of exposed surfaces

(2) Accidental flooding of watertight compartment with watertight openings shall be considered in addition if this would result in a more severe condition.

(3) The permeability of a damaged compartment shall be assumed to be 0.95. For machinery

spaces, a permeability = 0.85.

(4) In the final stage of flooding after damage, the positive range of the GZ curve shall be mini- mum 7° in conjunction with a height of not less than 0.05 m within this range. Unprotected

openings shall not be immersed within this range unless the space concerned is assumed to be flooded. The angle of heel after flooding shall not exceed 15°. The final waterline after flood-

Ch 4 Freeboard and Stability Ch 4

(5)

ing is to be below the lower edge of any weathertight opening through which progressive flood- ing may take place unless the space concerned is assumed to be flooded. It may be required to calculate the stability about additional axis to determine the most onerous result.

The stability at intermediate stages of flooding after damage shall not be significantly less than in the final stage.

(6) The flooding of any damaged compartment shall not render vital safety functions inoperative.

(7) For the purpose of damage stability calculations, a damage extent of 5 m horizontally along the surface shall be assumed for all exposed surfaces except the cargo deck. Watertight bulkheads

may be

ceeds 5 and the

tension

considered to remain intact provided that the distance between adjacent bulkheads ex-

m. The damage penetration into the structure shall be assumed to be equal to 0.76 m vertical extent of damage is assumed to be from the cargo deck or its horizontal ex- upwards without limit. For the cargo deck a damage extent of 5 × 5 m shall be

assumed. Watertight bulkheads may be considered to remain intact provided that the distance be- tween adjacent bulkheads exceeds 5 m. The damage penetration into the cargo deck shall be as-

sumed to be equal to 0.76 m.