4.29 Stability in Damaged Condition:

 (1) Sufficient intact stability shall be provided in all service conditions so as to enable the ship to withstand the final stage of flooding of any one main compartment which is required to be within the floodable length.

(2) Where two adjacent main compartments are separated by a bulkhead which is stepped under the conditions of section 4.28(7)(b) the intact stability shall be adequate to withstand the flooding of those two adjacent main compartments.

(3) Where the required factor of subdivision is 0.5 or less but more than 0.33 intact stability shall be adequate to withstand the flooding of any two adjacent main compartments.

(4) Where the required factor of subdivision is 0.33 or less the intact stability shall be adequate to withstand the flooding of any three adjacent main compartments.

(5) The requirements of subsections (1) to 4) shall be determined by calculations which are in accordance with subsections (11), (12) and (14) respectively and which take into consideration the proportions and design characteristics of the ship and the arrangement and configuration of the damaged compartments and in making these calculations the ship is to be assumed in the worst anticipated service condition as regards stability.

(6) Where it is proposed to fit decks, inner skins or longitudinal bulkheads of sufficient tightness to seriously restrict the flow of water, the Administration shall be satisfied that proper consideration is given to such restrictions in the calculations.

(7) The stability required in the final condition after damage, and after equalization where provided, shall be such that the positive residual righting lever curve shall have a minimum range of 15° beyond the angle of equilibrium provided that this range may be reduced to a minimum of 10°, in the case where the area under the righting lever curve is that specified in subsection (8), increased by the ratio-

where the range is expressed in degrees.

(8) The area under the righting lever curve shall be at least 0.015 metre-radians, measured from the angle of equilibrium to the lesser of-

• (a) the angle at which progressive flooding occurs; or

• (b) 22° (measured from the upright) in the case of one-compartment flooding, or 27° (measured from the upright) in the case of the simultaneous flooding of two or more adjacent compartments.

(9) A residual righting lever is to be obtained within the range of positive stability, taking into account the greatest of the following heeling moments-

• (a) the crowding of all passengers towards one side;

• (b) the launching of all fully loaded davit-launched survival craft on one side; and

• (c) due to wind pressure,

• as calculated by the formula-

  • GZ (in metres) = (Heeling moment/Displacement) + 0.04,

• provided that in no case is the righting lever to be less than 0.1 metres.

(10) For the purpose of calculating the heeling moments in subsection (9), the following assumptions shall be made-

• (a) moments due to crowding of passengers allowing-

  • (i) four persons per square metre;

  • (ii) a mass of 75 kg for each passenger,

  • and passengers shall be distributed on available deck areas towards one side of the ship on the decks where muster stations are located and in such a way that they produce the most adverse heeling moment;

• (b) moments due to launching of all fully loaded davit-launched survival craft on one side under the following conditions;

  • (i) all lifeboats and rescue boats fitted on the side to which the ship has heeled after having sustained damage shall be assumed to be swung out fully loaded and ready for lowering;

  • (ii) for lifeboats which are arranged to be launched fully loaded from the stowed position, the maximum heeling moment during launching shall be taken;

  • (iii) a fully loaded davit-launched liferaft attached to each davit on the side to which the ship has heeled after having sustained damage shall be assumed to be swung out ready for lowering;

  • (iv) persons not in the life-saving appliances which are swung out shall not provide either additional heeling or righting moment; and

  • (v) life-saving appliances on the side of the ship opposite to the side to which the ship has heeled shall be assumed to be in a stowed position;

• (c) moments due to wind pressure where-

  • (i) a wind pressure of 120 N/m² to be applied;

  • (ii) the area applicable shall be the projected lateral area of the ship above the waterline corresponding to the intact condition; and

  • (iii) the moment arm shall be the vertical distance from a point at one half of the mean draught corresponding to the intact condition to the centre of gravity of the lateral area;

• (d) in intermediate stages of flooding, the maximum righting lever shall be at least 0.05 metres and the range of positive righting levers shall be at least 7° provided that in all cases, only one breach in the hull and only one free surface need be assumed.

(11) For the purpose of making damage stability calculations the volume and surface permeabilities shall be in general as follows-

provided that higher surface permeabilities are to be assumed in respect of spaces which, in the vicinity of the damage waterplane, contain no substantial quantity of accommodation or machinery and spaces which are not generally occupied by any substantial quantity of stores.

(12) The assumed extent of damage shall be as follows-

• (a) in the longitudinal extent, 3 metres plus 3% of the length (L) of the ship, or 11 metres, whichever is the less, provided that where the required factor of subdivision is 0.33 or less the assumed longitudinal extent of damage shall be increased as necessary so as to include any two consecutive main transverse watertight bulkheads;

• (b) in the transverse extent (measured inboard from the ship's side, at right angles to the centreline at the level of the deepest subdivision load line) a distance of one fifth of the breadth of the ship, as defined in section 1.3; and

• (c) in the vertical extent: from the base line upwards without limit;

• provided that if any damage of lesser extent than that indicated in this paragraph would result in a more severe condition regarding heel or loss of metacentric height, such damage shall be assumed in the calculations.

(13) The following provisions apply with respect to unsymmetrical flooding-

• (a) Such flooding is to be kept to a minimum consistent with efficient arrangements;

• (b) where it is necessary to correct large angles of heel, the means adopted shall, where practicable, be self-acting, but in any case where controls to cross-flooding fittings are provided they shall be operable from above the bulkhead deck;

• (c) the cross-flooding fittings, together with their controls, shall be acceptable to the Administration;

• (d) the maximum angle of heel after flooding but before equalisation shall not exceed 15°;

• (e) where cross-flooding fittings are required the time for equalisation shall not exceed 15 minutes; and

• (f) suitable information concerning the use of cross-flooding fittings shall be supplied to the master of the ship^footnote.

(14) The final conditions of the ship after damage and, in the case of unsymmetrical flooding, after equalization measures have been taken shall be as follows-

• (a) in the case of symmetrical flooding there shall be a positive residual metacentric height of at least 50 millimetres as calculated by the constant displacement method;

• (b) in the case of unsymmetrical flooding, the angle of heel for one-compartment flooding shall not exceed 7° and for the simultaneous flooding of two or more adjacent compartments, a heel of 12° may be permitted by the Administration; and

• (c) in no case shall the margin line be submerged in the final stage of flooding and if it is considered that the margin line may become submerged during an intermediate stage of flooding, the Administration may require such investigations and arrangements as it considers necessary for the safety of the ship.

(15) The master of the ship shall be supplied with the data necessary to maintain sufficient intact stability under service conditions to enable the ship to withstand the critical damage ad in the case of ships requiring cross-flooding the master of the ship shall be informed of the conditions of stability on which the calculations of heel are based and be warned that excessive heeling might result should the ship sustain damage when in a less favourable condition.

(16) The data referred to in subsection (15) to enable the master to maintain sufficient intact stability shall include information which indicates the maximum permissible height of the ship's centre of gravity above keel (KG), or alternatively the minimum permissible metacentric height (GM), for a range of draughts or displacements sufficient to include all service conditions and the information shall show the influence of various trims taking into account the operational limits

(17) Datum draught marks should be provided at the bow and stern, port and starboard, in accordance with the following provisions-

• (a) they shall be adequate for assessing the condition and trim of the vessel;

• (b) the draught marks may be single datum lines;

• (c) the marks should be permanent and easily read but need not be of contrasting colour to the hull;

• (d) the marks need not indicate more than one draught at each position and should be above, but within 1000 millimetres, of the deepest load waterline; and

• (e) in the case where the draught marks are not located where they are easily readable or operational constraints for a particular trade make it difficult to read the draft marks,, then the ship shall also be fitted with a reliable draught indicating system by which the bow and stern draughts can be determined.

(18) The draught to which marks relate should be indicated either above the mark on the hull and/or in the stability information booklet for the vessel and the position of the marks should be verified at initial placement by the Administration or the vessel’s Assigning Authority.

(19) Where a reliable draught indicating system is fitted as required by subsection (17) consideration will be given to dispensing with the provision of draught marks.

(20) On completion of loading of the ship and prior to its departure, the master shall determine the ship's trim and stability and also ascertain and record that the ship is in compliance with the approved stability criteria and the determination of the ship's stability shall always be made by calculation, provided that the Administration may accept the use of an electronic loading and stability computer or equivalent means for this purpose.

(21) No relaxation from the requirements for damage stability may be considered by the Administration unless it is shown that the intact metacentric height in any service condition necessary to meet these requirements is excessive for the service intended.

(22) Relaxations from the requirements for damage stability shall be permitted only in exceptional cases and subject to the condition that the Administration is to be satisfied that the proportions, arrangements and other characteristics of the ship are the most favourable to stability after damage which can practically and reasonably be adopted in the particular circumstances.