Regulation 7-2 - Calculation of the factor si
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Statutory Documents - IMO Publications and Documents - Circulars - Maritime Safety Committee - MSC.1/Circular.1226 – Interim Explanatory Notes to the SOLAS Chapter II-1 Subdivision and Damage Stability Regulations – (15 January 2007) - Annex - Interim Explanatory Notes to the SOLAS Chapter II-1 Subdivision and Damage Stability Regulations - Part B - Guidance on Individual Regulations - Regulation 7-2 - Calculation of the factor si

Regulation 7-2 - Calculation of the factor si

Parent topic: Part B - Guidance on Individual Regulations

General

 Initial condition - an intact loading condition to be considered in the damage analysis described by the mean draught, vertical centre of gravity and the trim. Or alternative parameters from where the same may be determined (ex. displacement, GM and trim). There are three initial conditions corresponding to the three draughts ds , dp and dl .

 Immersion limits – immersion limits are an array of points that are not to be immersed at various stages of flooding as indicated in paragraphs 5.2 and 5.3 of the regulation.

 Openings – all openings need to be defined: both weathertight and unprotected. Openings are the most critical factor to preventing an inaccurate index A. If the final waterline immerses the lower edge of any opening through which progressive flooding takes place, the factor "s" may be recalculated taking such flooding into account. However, in this case the s value should also be calculated without taking into account progressive flooding and corresponding opening. The smallest s value should be retained for the contribution to the attained index.

Paragraph 2

Intermediate stages of flooding

 The case of instantaneous flooding in unrestricted spaces in way of the damage zone does not require intermediate stage flooding calculations. Where intermediate stages of flooding calculations are necessary in connection with progressive flooding, they should reflect the sequence of filling as well as filling level phases. Calculations for intermediate stages of flooding should be performed whenever equalization is not instantaneous, i.e. equalization is of a duration greater than 60 s. Such calculations consider the progress through one or more floodable (non-watertight) spaces. Bulkheads surrounding refrigerated spaces, incinerator rooms and longitudinal bulkheads fitted with non-watertight doors are typical examples of structures that may significantly slow down the equalization of main compartments.

Flooding boundaries

 If a compartment contains decks, inner bulkheads, structural elements and doors of sufficient tightness and strength to seriously restrict the flow of water, for intermediate stage flooding calculation purposes it should be divided into corresponding non-watertight spaces. It is assumed that the non-watertight divisions considered in the calculations are limited to "A" class fire-rated bulkheads and do not apply to "B" class fire-rated bulkheads normally used in accommodation areas (e.g. cabins and corridors). This guidance also relates to regulation 4, paragraph 4.

Sequential flooding computation

 For each damage scenario, the damage extent and location determine the initial stage of flooding. Calculations should be performed in stages, each stage comprising of at least two intermediate filling phases in addition to the full phase per flooded space. Unrestricted spaces in way of damage should be considered as flooded immediately. Every subsequent stage involves all connected spaces being flooded simultaneously until an impermeable boundary or final equilibrium is reached. If due to the configuration of the subdivision in the ship it is expected that other intermediate stages of flooding are more onerous, then those should be investigated.

Cross flooding/equalization

 In general, cross flooding is meant as a flooding of an undamaged space on the other side of the ship to reduce the heel in the final equilibrium condition.

 The cross-flooding time should be calculated in accordance with resolution A.266(VIII). If complete fluid equalization occurs in 60 s or less, it should be treated as instantaneous and no further calculations need to be carried out. Only passive open cross-flooding arrangements without valves should be considered effective for instantaneous flooding cases.

 If complete fluid equalization can be finalized in 10 min or less, the assessment of survivability can be carried out for passenger ships as the smallest values of sintermediate,i or sfinal .

 In case the equalization time is longer than 10 min, sfinal is calculated for the floating position achieved after 10 min of equalization. This floating position is computed by calculating the amount of flood water according to resolution A.266(VIII) using interpolation, where the equalization time is set to 10 min, i.e. the interpolation of the flood water volume is made between the case before equalization (T = 0) and the total calculated equalization time.

 In any cases where complete fluid equalization exceeds 10 min, the value of sfinal used in the formula in paragraph 1.1 should be the minimum of sfinal, i at 10 min or at final equalization.

Paragraph 4

 The displacement is the intact displacement at the subdivision draught in question (ds , dp and dl ).

Paragraph 4.1.1

 The beam B used in this paragraph means breadth as defined in regulation 2.8.

Paragraph 4.1.2

 The parameter A (projected lateral area) used in this paragraph does not refer to the attained subdivision index.

Paragraph 5

 In cargo ships where cross flooding devices are fitted, the safety of the ship should be maintained in all stages of flooding. The Administration may request for this to be demonstrated. Cross-flooding equipment, if installed, should have the capacity to ensure that the equalization takes place within 10 min.

Paragraph 5.2.1

Unprotected openings

 The flooding angle will be limited by immersion of such an opening. It is not necessary to define a criterion for non-immersion of unprotected openings at equilibrium, because if it is immersed, the range of positive GZ limited to flooding angle will be zero so "s" will be equal to zero.

 An unprotected opening connects two rooms or one room and the outside. An unprotected opening will not be taken into account if the two connected rooms are flooded or none of these rooms are flooded. If the opening is connected to the outside, it will not be taken into account if the connected compartment is flooded. An unprotected opening does not need to be taken into account if it connects a flooded room or the outside to an undamaged room, if this room will be considered as flooded in a subsequent stage.

Openings fitted with a weathertight mean of closing ("weathertight openings")

 The survival "s" factor will be "0" if any such point is submerged at a stage which is considered as "final". Such points may be submerged during a stage or phase which is considered as "intermediate", or within the range beyond equilibrium.

 If an opening fitted with a weathertight means of closure is submerged at equilibrium during a stage considered as intermediate, it should be demonstrated that this weathertight means of closure can sustain the corresponding head of water and that the leakage rate is negligible.

 These points are also defined as connecting two rooms or one room and the outside, and the same principle as for unprotected openings is applied to take them into account or not. If several stages have to be considered as "final", a "weathertight opening" does not need to be taken into account if it connects a flooded room or the outside to an undamaged room if this room will be considered as flooded in a successive "final" stage.

Paragraph 5.2.2

 Horizontal evacuation routes on the bulkhead deck include only escape routes (designated as category 2 stairway spaces according to SOLAS regulation II-2/9.2.2.3 or as category 4 stairway spaces according to SOLAS regulation II-2/9.2.2.4 for passenger ships carrying not more than 36 passengers) used for the evacuation of undamaged spaces. Horizontal evacuation routes do not include corridors within the damaged space. No part of a horizontal evacuation route should be immersed.

 The provisions for escape in SOLAS chapter II-2 may allow more than one watertight compartment below the bulkhead deck to be served by a common stairway within the same main vertical zone (MVZ). Partial immersion of the bulkhead deck may be accepted at final equilibrium. The new provision is intended to ensure that evacuation along the bulkhead deck to the vertical escapes will not be impeded by water on that deck. A "horizontal evacuation route" in the context of this regulation means a route on the bulkhead deck connecting spaces located on and under this deck with the vertical escapes from the bulkhead deck required for compliance with SOLAS chapter II-2.

Paragraph 5.3.1

 The purpose of this paragraph is to provide an incentive to ensure that evacuation through a vertical escape will not be obstructed by water from above. The paragraph is intended for smaller emergency escapes, typically hatches, where fitting of a watertight or weathertight means of closure would otherwise exclude them from being considered as flooding points.

 Since the probabilistic regulations do not require that the watertight bulkheads be carried continuously up to the bulkhead deck, care should be taken to ensure that evacuation from intact spaces through flooded spaces below the bulkhead deck will remain possible, for instance by means of a watertight trunk.

Paragraph 6

 The sketches in the figure illustrate the connection between position of watertight decks in the reserve buoyancy area and the use of factor v for damages below these decks.

In this example, there are 3 horizontal subdivisions to be taken into account as the vertical extent of damage.The example shows the maximum possible vertical extent of damage d + 12.5 m is positioned between H2 and H3 . H1 with factor v1 , H2 with factor v2 > v1 but v2 < 1 and H3 with factor v3 = 1.
The factors v1 and v2 are the same as above. The reserve buoyancy above H3 should be taken undamaged in all damage cases.
The combination of damages into the rooms R1, R2 and R3 positioned below the initial water line should be chosen so that the damage with the lowest s-factor is taken into account. That often results in the definition of alternative damages to be calculated and compared. If the deck taken as lower limit of damage is not watertight, down flooding should be considered.

Paragraph 6.1

 The parameters x1 and x2 are the same as parameters x1 and x2 used in regulation 7-1.

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