Regulation 7.1
1 The probability of surviving after collision damage to the ship's hull is expressed by
the index A. Producing an index A requires calculation of various damage
scenarios defined by the extent of damage and the initial loading conditions of the ship
before damage. Three loading conditions should be considered and the result weighted as
follows:
where the indices s, p and l represent the three loading conditions
and the factor to be multiplied to the index indicates how the index A from each
loading condition is weighted.
2 The method of calculating A for a loading condition is expressed by the
formula:
2.1 The index c represents one of the three loading conditions, the index i
represents each investigated damage or group of damages and t is the number of
damages to be investigated to calculate Ac for the particular loading
condition.
2.2 To obtain a maximum index A for a given subdivision, t has to be equal
to T, the total number of damages.
3 In practice, the damage combinations to be considered are limited either by
significantly reduced contributions to A (i.e. flooding of substantially larger
volumes) or by exceeding the maximum possible damage length.
4 The index A is divided into partial factors as follows:
-
pi The p factor is solely dependent
on the geometry of the watertight arrangement of the ship.
-
vi The v factor is dependent on the geometry
of the watertight arrangement (decks) of the ship and the draught of the initial
loading condition. It represents the probability that the spaces above the
horizontal subdivision will not be flooded.
-
si The s factor is dependent on the
calculated survivability of the ship after the considered damage for a specific
initial condition.
5 Three initial loading conditions should be used for calculating each index
A. The loading conditions are defined by their mean draught d, trim
and GM
(or KG). The mean draught and trim are illustrated in the figure
below.
6 The GM (or KG) values for the three loading conditions could, as a first
attempt, be taken from the intact stability GM (or KG) limit curve. If the
required index R is not obtained, the GM (or KG) values may be
increased (or reduced), implying that the intact loading conditions from the intact
stability book must now meet the GM (or KG) limit curve from the damage
stability calculations derived by linear interpolation between the three GMs.
7 For a series of new passenger or cargo ships built from the same plans each of which
have the same draughts ds, dp and
dl as well as the same GM and trim limits, the attained
subdivision index A calculated for the lead ship may be used for the other ships.
In addition, small differences in the draught dl (and the subsequent
change in the draught dp) are acceptable if they are due to small
differences in the lightship characteristics that do not exceed the deviation limits
specified in regulation 5.2. For cases where these conditions are not met, a new
attained subdivision index A should be calculated.
"Built from the same plans" means that the watertight and weathertight
aspects of the hull, bulkheads, decks, openings and other parts of a ship that impact
the attained subdivision index A calculation remain exactly the same.
8 For a passenger or cargo ship in service which undergoes alterations that materially
affect the stability information supplied to the master and require it to be re-inclined
in accordance with regulation 5.4, a new attained subdivision index A should be
calculated. However, for alteration cases where a re-inclining is not required and the
alterations do not change the watertight and weathertight arrangements of the ship that
impact the attained subdivision index A, if ds and the
GM and trim limits remain the same then a new attained subdivision index
A is not required.
9 For passenger ships subject to lightweight surveys every 5 years, if the lightweight
survey results are within the limits specified in regulation 5.5, and
ds and the GM and trim limits remain the same, a new
attained subdivision index A is not required. However, if the lightweight survey
results exceed either limit specified in regulation 5.5, a new attained subdivision
index A should be calculated.
10 For any new passenger or cargo ship for which the deviation in lightship
characteristics between the preliminary and the as built values are within the limits
specified in regulation 5.2 and ds is unchanged, then the preliminary
attained subdivision index A calculation may be approved as the final attained
subdivision index A calculation. However, for cases where these conditions are
not met, then a new attained subdivision index A should be calculated.
Regulation 7.2
When additional calculations of A are performed for different trims, for a given
set of calculations the difference between trim values for ds,
dp and dl may not exceed 1% L.
Regulation 7.5
1 With the same intent as wing tanks, the summation of the attained index A should
reflect effects caused by all watertight bulkheads and flooding boundaries within the
damaged zone. It is not correct to assume damage only to one half of the ship's breadth
B and ignore changes in subdivision that would reflect lesser
contributions.
2 In the forward and aft ends of the ship where the sectional breadth is less than the
ship's breadth B, transverse damage penetration can extend beyond the centreline
bulkhead. This application of the transverse extent of damage is consistent with the
methodology to account for the localized statistics which are normalized on the greatest
moulded breadth B rather than the local breadth.
3 Where, at the extreme ends of the ship, the subdivision exceeds the
waterline at the deepest subdivision draught, the damage penetration b or
B/2 is to be taken from centreline. The figure below illustrates the shape of
the B/2 line.
4 Where longitudinal corrugated bulkheads are fitted in wing compartments or on the
centreline, they may be treated as equivalent plane bulkheads provided the corrugation
depth is of the same order as the stiffening structure. The same principle may also be
applied to transverse corrugated bulkheads.
Regulation 7.6
Refer to the explanatory notes for regulation 7-2.2 for the treatment of free surfaces
during all stages of flooding.
Regulation 7.7
1 This explanatory note only applies to ships for which the building
contract is placed on or after 1 January 2020 and which are constructed before 1
January 2024. Pipes and valves directly adjacent or situated as close as
practicable to a bulkhead or to a deck can be considered to be part of the bulkhead or
deck, provided the separation distance on either side of the bulkhead or deck is of the
same order as the bulkhead or deck stiffening structure. The same applies for small
recesses, drain wells, etc.
2 This explanatory note only applies to ships constructed on or after 1 January
2024. Pipes and valves directly adjacent or situated as close as practicable to
a bulkhead or to a deck can be considered to be part of the bulkhead or deck, provided
the separation distance on either side of the bulkhead or deck is of the same order as
the bulkhead or deck stiffening structure. The same applies for small recesses, drain
wells, etc. In no case should the separation distance on either side of the bulkhead or
deck be more than 450 mm measured from the valve's near end to the bulkhead or deck.
3 For ships up to L = 150 m the provision for allowing "minor
progressive flooding" should be limited to pipes penetrating a watertight subdivision
with a total cross-sectional area of not more than 710 mm2 between any two
watertight compartments. For ships of L = 150 m and upwards the total
cross-sectional area of pipes should not exceed the cross-sectional area of one pipe
with a diameter of L/5000 m.