Ship Survival Capability and Location of Cargo Tanks

2.1.1 Ships, subject to the Code, shall survive the normal effects of flooding following assumed hull damage caused by some external force. In addition, to safeguard the ship and the environment, the cargo tanks of certain types of ships shall be protected from penetration in the case of minor damage to the ship resulting, for example, from contact with a jetty or tug, and given a measure of protection from damage in the case of collision or stranding, by locating them at specified minimum distances inboard from the ship’s shell plating. Both the assumed damage and the proximity of the cargo tanks to the ship’s shell shall be dependent upon the degree of hazard presented by the products to be carried.

2.1.2 Ships subject to the Code shall be designed to one of the following standards:

1. A type 1 ship is a chemical tanker intended to transport chapter 17 products with very severe environmental and safety hazards which require maximum preventive measures to preclude an escape of such cargo.

2. A type 2 ship is a chemical tanker intended to transport chapter 17 products with appreciably severe environmental and safety hazards which require significant preventive measures to preclude an escape of such cargo.

3. A type 3 ship is a chemical tanker intended to transport chapter 17 products with sufficiently severe environmental and safety hazards which require a moderate degree of containment to increase survival capability in a damaged condition.

Thus, a type 1 ship is a chemical tanker intended for the transportation of products considered to present the greatest overall hazard and type 2 and type 3 for products of progressively lesser hazards. Accordingly, a type 1 ship shall survive the most severe standard of damage and its cargo tanks shall be located at the maximum prescribed distance inboard from the shell plating.

2.1.3 The ship type required for individual products is indicated in column e in the table of chapter 17.

2.1.4 If a ship is intended to carry more than one product listed in chapter 17, the standard of damage shall correspond to that product having the most stringent ship type requirement. The requirements for the location of individual cargo tanks, however, are those for ship types related to the respective products intended to be carried.

2.2.1 Ships subject to the Code may be assigned the minimum freeboard permitted by the International Convention on Load Lines in force. However, the draught associated with the assignment shall not be greater than the maximum draught otherwise permitted by this Code.

2.2.2 The stability of the ship in all seagoing conditions shall be to a standard which is acceptable to the Administration.

2.2.3 When calculating the effect of free surfaces of consumable liquids for loading conditions it shall be assumed that, for each type of liquid, at least one transverse pair or a single centre tank has a free surface and the tank or combination of tanks to be taken into account shall be those where the effect of free surfaces is the greatest. The free surface effect in undamaged compartments shall be calculated by a method acceptable to the Administration.

2.2.4 Solid ballast shall not normally be used in double-bottom spaces in the cargo area. Where, however, because of stability considerations, the fitting of solid ballast in such spaces becomes unavoidable, then its disposition shall be governed by the need to ensure that the impact loads resulting from bottom damage are not directly transmitted to the cargo tank structure.

2.2.5 The master of the ship shall be supplied with a loading and stability information booklet. This booklet shall contain details of typical service and ballast conditions, provisions for evaluating other conditions of loading and a summary of the ship’s survival capabilities. In addition, the booklet shall contain sufficient information to enable the master to load and operate the ship in a safe and seaworthy manner.

2.3.1 The provision and control of valves fitted to discharges led through the shell from spaces below the freeboard deck or from within the super-structures and deck-houses on the freeboard deck fitted with weathertight doors shall comply with the requirements of the relevant regulation of the International Convention on Load Lines in force, except that the choice of valves shall be limited to:

1. one automatic non-return valve with a positive means of closing from above the freeboard deck; or

2. where the vertical distance from the summer load waterline to the inboard end of the discharge pipe exceeds 0.01L, two automatic non-return valves without positive means of closing, provided that the inboard valve is always accessible for examination under service conditions.

2.3.2 For the purpose of this chapter, “summer load line” and “freeboard deck” have the meanings as defined in the Load Lines, 1966/1988 - International Convention on Load Lines, 1966, as Amended by the Protocol of 1988 in force.

2.3.3 The automatic non-return valves referred to in Ch 1, 2.3 Shipside discharges below the freeboard deck 2.3.1 and Ch 1, 2.3 Shipside discharges below the freeboard deck 2.3.1.(b) shall be fully effective in preventing admission of water into the ship, taking into account the sinkage, trim and heel in survival requirements in Ch 1, 2.9 Survival requirements, and shall comply with recognized standards.

2.4.1 Damage survival capability should be investigated on the basis of loading information submitted to the Administration for all anticipated conditions of loading and variations in draught and trim. Ballast conditions where the chemical tanker is not carrying products covered by the Code, or is carrying only residues of such products, need not be considered.

2.5.1 The assumed maximum extent of damage shall be:

2.5.2 If any damage of a lesser extent than the maximum damage specified in Ch 1, 2.5 Damage assumptions 2.5.1 would result in a more severe condition, such damage shall be considered.

2.6.1 Cargo tanks shall be located at the following distances inboard:

1. Type 1 ships: from the side shell plating, not less than the transverse extent of damage specified in Ch 1, 2.5 Damage assumptions, and from the moulded line of the bottom shell plating at centreline, not less than the vertical extent of damage specified in Ch 1, 2.5 Damage assumptions, and nowhere less than 760 mm from the shell plating. This requirement does not apply to the tanks for diluted slops arising from tank washing.

2. Type 2 ships: from the moulded line of the bottom shell plating at centreline, not less than the vertical extent of damage specified in Ch 1, 2.5 Damage assumptions, and nowhere less than 760 mm from the shell plating. This requirement does not apply to the tanks for diluted slops arising from tank washing.

3. Type 3 ships: no requirement.

2.6.2 Except for type 1 ships, suction wells installed in cargo tanks may protrude into the vertical extent of bottom damage specified in Ch 1, 2.5 Damage assumptions provided that such wells are as small as practicable and the protrusion below the inner bottom plating does not exceed 25% of the depth of the double bottom or 350 mm, whichever is less. Where there is no double bottom, the protrusion of the suction well of independent tanks below the upper limit of bottom damage shall not exceed 350 mm. Suction wells installed in accordance with this paragraph may be ignored in determining the compartments affected by damage.

2.7.1 The requirements of Ch 1, 2.9 Survival requirements shall 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, relative densities and the free surface effects of liquids; and the draught and trim for all conditions of loading.

2.7.2 The permeabilities of spaces assumed to be damaged shall be as follows:

2.7.3 Wherever damage penetrates a tank containing liquids it shall be assumed that the contents are completely lost from that compartment and replaced by salt water up to the level of the final plane of equilibrium.

2.7.4 Every watertight division within the maximum extent of damage defined in Ch 1, 2.5 Damage assumptions 2.5.1 and considered to have sustained damage in positions given in Ch 1, 2.8 Standard of damage 2.8.1 shall be assumed to be penetrated. Where damage less than the maximum is being considered in accordance with Ch 1, 2.5 Damage assumptions 2.5.2, only watertight divisions or combinations of watertight divisions within the envelope of such lesser damage shall be assumed to be penetrated.

2.7.5 The ship shall be so designed as to keep unsymmetrical flooding to the minimum consistent with efficient arrangements.

2.7.6 Equalization arrangements requiring mechanical aids such as valves or cross-levelling pipes, if fitted, shall not be considered for the purpose of reducing an angle of heel or attaining the minimum range of residual stability to meet the requirements of Ch 1, 2.9 Survival requirements and sufficient residual stability shall be maintained during all stages where equalization is used. Spaces which are linked by ducts of large cross-sectional area may be considered to be common.

2.7.7 If pipes, ducts, trunks or tunnels are situated within the assumed extent of damage penetration, as defined in Ch 1, 2.5 Damage assumptions, arrangements shall be such that progressive flooding cannot thereby extend to compartments other than those assumed to be flooded for each case of damage.

2.7.8 The buoyancy of any superstructure directly above the side damage shall be disregarded. The unflooded parts of superstructures beyond the extent of damage, however, may be taken into consideration provided that:

1. they are separated from the damaged space by watertight divisions and the requirements of Ch 1, 2.9 Survival requirements 2.9.3 in respect of these intact spaces are complied with; and

2. openings in such divisions are capable of being closed by remotely operated sliding watertight doors and unprotected openings are not immersed within the minimum range of residual stability required in Ch 1, 2.9 Survival requirements; however, the immersion of any other openings capable of being closed weathertight may be permitted.

2.8.1 Ships shall be capable of surviving the damage indicated in Ch 1, 2.5 Damage assumptions with the flooding assumptions in Ch 1, 2.7 Flooding assumptions to the extent determined by the ship's type according to the following standards:

1. A type 1 ship shall be assumed to sustain damage anywhere in its length.

2. A type 2 ship of more than 150 m in length shall be assumed to sustain damage anywhere in its length.

3. A type 2 ship of 150 m in length or less shall be assumed to sustain damage anywhere in its length except involving either of the bulkheads bounding a machinery space located aft.

4. A type 3 ship of more than 225 m in length shall be assumed to sustain damage anywhere in its length.

5. A type 3 ship of 125 m in length or more but not exceeding 225 m in length shall be assumed to sustain damage anywhere in its length except involving either of the bulkheads bounding a machinery space located aft.

6. A type 3 ship below 125 m in length shall be assumed to sustain damage anywhere in its length except involving damage to the machinery space when located aft. However, the ability to survive the flooding of the machinery space shall be considered by the Administration.

2.8.2 In the case of small type 2 and type 3 ships which do not comply in all respects with the appropriate requirements of Ch 1, 2.8 Standard of damage 2.8.1.(c) and Ch 1, 2.8 Standard of damage 2.8.1.(f), special dispensation may only be considered by the Administration provided that alternative measures can be taken which maintain the same degree of safety. The nature of the alternative measures shall be approved and clearly stated and be available to the port Administration. Any such dispensation shall be duly noted on the International Certificate of Fitness referred to in 1.5.4 Issue of International Certificate of Fitness.

2.9.1 Ships subject to the Code shall be capable of surviving the assumed damage specified in Ch 1, 2.5 Damage assumptions to the standard provided in Ch 1, 2.8 Standard of damage in a condition of stable equilibrium and should satisfy the following criteria.

2.9.2 In any stage of flooding:

1. The waterline, taking into account sinkage, heel and trim, shall be below the lower edge of any opening through which progressive flooding or downflooding may take place. Such openings shall include air pipes and openings which are closed by means of weathertight doors or hatch covers and may exclude those openings closed by means of watertight manhole covers and watertight 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. the maximum angle of heel due to unsymmetrical flooding shall not exceed 25°, except that this angle may be increased to 30° if no deck immersion occurs;

3. the residual stability during intermediate stages of flooding shall be to the satisfaction of the Administration. However, it shall never be significantly less than that required by Ch 1, 2.9 Survival requirements 2.9.3.

2.9.3 At final equilibrium after flooding:

1. the righting-lever curve shall have a minimum range of 20° beyond the position of equilibrium in association with a maximum residual righting lever of at least 0.1 m within the 20° range; the area under the curve within this range should not be less than 0.0175 m rad. Unprotected openings should not be immersed within this range unless the space concerned is assumed to be flooded. Within this range, the immersion of any of the openings listed in Ch 1, 2.9 Survival requirements 2.9.2 and other openings capable of being closed weathertight may be permitted; and

2. the emergency source of power shall be capable of operating.