Chapter 2 – Stability & Subdivision
[May apply to special purpose ships certified before 13-05-2008]
2.1 The intact stability of special purpose ships of under 100 m in length should comply with the provisions in resolution A.167(ES.IV) except that the alternative criteria given in 2.5.2 of the Guidelines for the Design and Construction of Offshore Supply Vessels may be used for special purpose ships of similar design and characteristics. The intact stability of special purpose ships of 100 m in length and above should be to the satisfaction of the Administration.
2.2 The subdivision and damage stability of special purpose ships carrying not more than 200 special personnel should be adequate to meet the survival standard specified in 2.5, after sustaining assumed side damage to the extent given in 2.3, in locations along the ship’s length as specified in 2.2.1 and 2.2.2 for any condition of loading. These requirements should govern this operating draught for any actual condition of loading provided the draught is in no case greater than that corresponding to the minimum freeboard calculated in accordance with the International Convention on Load Lines in force.
2.2.1 In a special purpose ship carrying not more than 50 special personnel the damage should be assumed to occur anywhere in its length between transverse watertight bulkheads, spaced at a distance of not less than the longitudinal extent of side damage specified in 2.3.1, except involving damage to the machinery space. A special purpose ship of not more than 50 m in length and carrying not more than 50 special personnel may be exempted from the subdivision requirements of this Code provided that it complies with safety requirements which the Administration may deem appropriate for the area of operation.
2.2.2 In a special purpose ship carrying more than 50 but not more than 200 special personnel the damage should be assumed to occur anywhere in its length between transverse watertight bulkheads spaced at a distance of not less than the longitudinal extent of side damage specified in 2.3.1. In any such special purpose ship having a length of 100 m and over the assumed damage at the forward end should include damage to the collision bulkhead. 2.2.3 A special purpose ship carrying more than 200 special personnel should meet the subdivision and damage stability requirements for a passenger ship carrying that number of passengers.
2.3 Subject to the provisions of this section the extent of damage should be assumed as follows:
2.3.1 Longitudinal extent: (1/3) × L(exp(2/3)) or 14.5 m, whichever is less.
2.3.2 Transverse extent: B/5 or 11.5 m, whichever is less (measured inboard from the ship’s side at right angles to the centreline at the level of the summer load line).
2.3.3 Vertical extent: from the moulded line of the bottom shell plating at centreline upwards without limit.
2.3.4 If any damage of a lesser extent than that specified in 2.3.1, 2.3.2 and/or 2.3.3 results in a more severe condition, such damage should be taken into account.
2.3.5 If pipes, ducts, trunks or tunnels are situated within the assumed extent of damage, arrangements should be such that progressive flooding cannot thereby extend to compartments other than those assumed to be flooded for each case of damage.
2.4 The requirements of 2.2 should be confirmed by calculations which take into consideration the design characteristics of the ship, the arrangements, configuration and contents of the damaged compartments, the distribution of dry cargo, the distribution, specific gravities and the free surface effect of liquids and should be based on the following provisions:
2.4.1 The permeability of spaces assumed to be damaged should be as follows:
Appropriated to cargo by calculation, but not less than 0.60
Appropriated to stores 0.60
Occupied by accommodation 0.95
Occupied by machinery 0.85
Intended for voids 0.95
2.4.2 Wherever as a result of assumed damage a tank is penetrated, it should be assumed that any liquid therein is completely lost from that compartment and replaced by salt water up to the level of the final plane of equilibrium.
2.5 The ship may be regarded as achieving the required survival standard if the following conditions are met:
2.5.1 The damage waterline before the equalization and/or in the process thereof should be below the lower edge of any opening through which progressive flooding may take place. Such openings include air-pipes, ventilators and openings which are closed by means of weathertight doors or hatch covers but 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.
2.5.2 The angle of heel due to unsymmetrical flooding should not exceed 20° prior to equalization and after equalization should not exceed:
7° – in the case of flooding between adjacent transverse watertight bulkheads as required in 2.2.1 and 2.2.2
12° – in the case of flooding involving the collision bulkhead as required in 2.2.2.
In special cases the Administration may allow additional heel due to the unsymmetrical moment but in no case should the final heel exceed 15°.
2.5.3 The initial metacentric height of a ship in the final stage of flooding for the static equilibrium position in case of symmetrical flooding and for the upright position in case of unsymmetrical flooding as calculated by the constant displacement method should be not less than 0.05 m before appropriate measures to increase the metacentric height have been taken.
2.5.4 The righting lever curve at the final stage of flooding should have a minimum range of 20° beyond the position of equilibrium in association with a maximum righting lever of at least 100 mm within this range. Unprotected openings should not be immersed within this range of residual stability except where the space concerned is included in damage stability calculations as a floodable space. Within this range the immersion of all openings listed in 2.5.1 and other openings capable of being closed watertight may be permitted.
2.5.5 The Administration should be satisfied that the damage stability and trim are sufficient during intermediate stages of flooding.
2.6 The ship should be designed so as to keep unsymmetrical flooding to a minimum consistent with efficient arrangements. The means adopted for equalization of the ship should, where practicable, be self-acting, but in any case where controls to cross-flooding fittings are provided they should be operable from above the bulkhead deck. All such fittings and controls should be acceptable to the Administration.
2.7 The requirements of regulations 9 to 20 and 22 to 25 of part B of chapter II-1 of the 1974 SOLAS Convention as amended should be met as follows:
1. Regulations 9, 12, 14, 18, 19, 22, 23, 24, 25 by all special purpose ships, as applicable;
2. Regulation 10 by special purpose ships carrying more than 50 special personnel;
3. Regulation 11 by special purpose ships carrying not more than 50 special personnel;
4. Regulations 17 and 20 by special purpose ships carrying more than 200 special personnel;
5. Regulation 15 for all special purpose ships except that for special purpose ships of not more than 50 m in length exemptions may be granted by the Administration;
6. Regulations 13 and 16 are not applicable.
2.8 Bilge pumping arrangements.
2.8.1 A ship carrying not more than 50 special personnel should meet the requirements of regulation 21.1 and 21.3 of part B of chapter II-1 of the 1974 SOLAS Convention as amended and the following:
1. The bilge pumping system required by regulation 21.1 should be capable of operation after side damage specified in 2.3 in the locations along the ship’s length specified in 2.2.1. For this purpose wing suctions should generally be fitted except in narrow compartments at the end of the ship, where one suction may be sufficient. In compartments of unusual form, additional suctions may be required. Arrangements should be made whereby water in the compartment may find its way to the suction pipes. Where, for particular compartments, the Administration is satisfied that the provision of drainage may be undesirable, it may allow such provisions to be dispensed with, provided the survival capability of the ship will not be impaired.
2. Provision should be made to prevent the compartment served by any bilge suction pipe being flooded in the event of the pipe being severed or otherwise damaged by collision in any other compartment. For this purpose, where the pipe is at any part situated within the transverse extent of damage, as specified in 2.3 in the locations along the ship’s length as specified in 2.2.1, a nonreturn valve should be fitted to the pipe in the compartment containing the open end.
3. Distribution boxes, cocks and valves in connection with the bilge pumping system should be arranged so that, in the event of flooding of a compartment other than the machinery space, one of the bilge pumps may be operative on any compartment; in addition, damage to a pump or pipe located outside the machinery space and connected to the bilge main outboard of the transverse extent of damage as specified in 2.3 in the locations along the ship’s length specified in 2.2.1 should not put the bilge pumping system out of action. The valves for controlling the bilge suctions for spaces other than the machinery space should be capable of being operated from within the machinery space or from above the bulkhead deck.
2.8.2 A special purpose ship of not more than 50 m in length and carrying not more than 50 special personnel may be exempted from 2.8.1, provided that it complies with the safety requirements which the Administration may deem appropriate for the area of operation.
2.8.3 A ship carrying more than 50 special personnel should meet the requirements of regulation 21.1 and 21.2 of part B of chapter II-1 of the 1974 SOLAS Convention as amended.
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