Taking into account, as initial conditions before flooding, the standard loading conditions as referred to in 220.127.116.11 and the damage assumptions in 4.2, the vessel should comply with the damage stability criteria as specified in 4.3.
4.2 Damage assumptions 4.2.1
Damage should be assumed to occur anywhere in the vessel's length between transverse watertight bulkheads.
The vertical extent of damage should be assumed from the underside of the cargo deck, or the continuation thereof, for the full depth of the vessel.
The transverse extent of damage should be assumed as 760 mm, measured inboard from the side of the vessel perpendicularly to the centreline at the level of the summer load waterline.
A transverse watertight bulkhead extending from the vessel's side to a distance inboard of 760 mm or more at the level of the summer load line joining longitudinal watertight bulkheads may be considered as a transverse watertight bulkhead for the purpose of the damage calculations.
If pipes, ducts or tunnels are situated within the assumed extent of damage, arrangements should be made to ensure that progressive flooding cannot thereby extend to compartments other than those assumed to be floodable for each case of damage.
If damage of a lesser extent than that specified in 4.2.2 or 4.2.3
results in a more severe condition, such lesser extent should be assumed.
Where a transverse watertight bulkhead is located within the transverse extent of assumed damage and is stepped in way of a double bottom or side tank by more than 3.05 m, the double bottom or side tanks adjacent to the stepped portion of the transverse watertight bulkhead should be considered as flooded simultaneously.
4.3 Damage stability criteria 4.3.1
The final waterline, taking into account sinkage, heel and trim, should be below the lower edge of any opening through which progressive flooding may take place. Such openings should include air pipes and those which are capable of being closed by means of weathertight doors or hatch covers and may exclude those openings closed by means of watertight manhole covers and flush scuttles, small watertight cargo tank hatch covers which maintain the high integrity of the deck, remotely operated watertight sliding doors, and sidescuttles of the non-opening type.
In the final stage of flooding, the angle of heel due to unsymmetrical flooding should not exceed 15°. This angle may be increased up to 17° if no deck immersion occurs.
The stability in the final stage of flooding should be investigated and may be regarded as sufficient if the righting lever curve has at least a range of 20° beyond the position of equilibrium in association with a maximum residual righting lever of at least 100 mm within this range. Unprotected openings should not become immersed at an angle of heel within the prescribed minimum range of residual stability unless the space in question has been included as a floodable space in calculations for damage stability. Within this range, immersion of any of the openings referred to in 4.3.1 and any other openings capable of being closed weathertight may be authorized.
The Head of the Shipping Inspectorate should be satisfied that the stability is sufficient during intermediate stages of flooding.
4.4 Assumptions for calculating damage stability 4.4.1
Compliance with 4.3 should be confirmed by calculations which take into consideration the design characteristics of the vessel, the arrangements, configuration and permeability of the damaged compartments and the distribution, specific gravities and the free surface effect of liquids.
The permeability of compartments assumed to be damaged should be as follows:
|Spaces ||Permeability |
|Appropriated to stores||0.60|
|Occupied by accommodation||0.95|
|Occupied by machinery||0.85|
|Intended for dry cargo||0.95|
The permeability of tanks should be consistent with the amount of liquid carried, as shown in the loading conditions specified in 3.1. The permeability of empty tanks should be assumed to be not less than 0.95.
The free surface effect should be calculated at an angle of heel of 5 degrees for each individual compartment or the effect of free surfaces of liquids in a tank should be calculated over the range of positive residual righting arm, by assessing the shift of liquids by moment of transference calculations.
Free surface for each type of consumable liquid should be assumed for at least one transverse pair of tanks or a single centreline tank. The tank or tanks to be taken into account should be those where the effect of free surface is the greatest.
Alternatively, the actual free surface effect may be used provided the methods of calculation are acceptable to the Head of the Shipping Inspectorate.