Chapter 2 - Vessel Survival Capability and Location of Cargo Tanks
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Chapter 2 - Vessel Survival Capability and Location of Cargo Tanks

 To ensure that the cargo tanks are located in protected location(s) for the event of minor hull damage and that the vessel can survive the assumed flooding conditions.

2.1 General

2.1.1 OSVs subject to the present Code should survive the normal effects of flooding following assumed hull damage caused by some external force. In addition, to safeguard the vessel and the environment, the cargo tanks should be protected from penetration in the case of minor damage to the vessel resulting, for example, from contact with a jetty or an offshore installation, 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 vessel's shell plating. Both the assumed damage and the proximity of the cargo tanks to the vessel's shell should be dependent upon the degree of hazard presented by the products to be carried.

2.1.2 The design standards of this chapter should be applied according to the ship type required for cargoes containing mixtures and individual products indicated in chapter 17 of the IBC Code and the latest edition of the MEPC.2 Circular.

2.1.3 OSVs subject to the present Code may be designed without cargo tank capacity limitation; however, the requirements of this chapter will be applied according to the ship type classified in the IBC Code and quantity of products carried on any single voyage.

2.1.4 If a vessel is intended to carry more than one product listed in chapter 17 of the IBC Code and the latest edition of the MEPC.2 Circular, the standard of damage should correspond to that product having the most stringent ship type provision. The provisions for the location of individual cargo tanks, however, need only be applied based upon the vessel types related to the respective products certified to be carried.

2.1.5 The provisions for cargo ships in SOLAS chapter II-1, parts B, B-1, B-2 and B-4, should apply to vessels covered by the present Code, except that SOLAS regulations II-1/6 to II-1/7-3 need not apply, unless expressly provided otherwise.

2.2 Freeboard and intact stability

2.2.1 OSVs subject to the present Code may be assigned the minimum freeboard permitted by the International Convention on Load Lines in force.

2.2.2 The intact stability of the vessel in all seagoing conditions should comply with the International Code on Intact Stability, 2008 (resolution MSC.267(85)), as amended.

2.2.3 Solid ballast should 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 should be governed by the need to ensure that the impact loads resulting from bottom damage are not directly transmitted to the cargo tank structure.

2.2.4 The master of the vessel should be supplied with a loading and stability information booklet. This booklet should contain details of typical service and ballast conditions, provisions for evaluating other conditions of loading and a summary of the vessel's survival capabilities. In addition, the booklet should contain sufficient information to enable the master to load and operate the vessel in a safe and seaworthy manner. All OSVs of 500 gross tonnage and above should comply with SOLAS regulation II-1/5-1.

2.2.5 OSVs subject to 2.6.1 and those vessels with a length of 80 m or more subject to 2.6.2 should be fitted with a stability instrumentfootnote capable of verifying compliance with intact and damage stability provisions, approved by the Administration, having regard to the performance standards recommended by the Organization.footnote

2.3 Non-cargo discharges below the freeboard deck

2.3.1 The provision and control of valves fitted to non-cargo discharges led through the shell from spaces below the freeboard deck or from within superstructures and deckhouses on the freeboard deck fitted with weathertight doors should comply with the requirements of the relevant regulation of the International Convention on Load Lines in force, except that the choice of valves should 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 International Convention on Load Lines in force.

2.3.3 The automatic non-return valves referred to in 2.3.1.1 and 2.3.1.2 should be fully effective in preventing admission of water into the vessel, taking into account the sinkage, trim and heel in survival provisions in 2.8, and should comply with recognized standards.

2.4 Conditions of loading

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 for the conditions for cargoes which the vessels is certified to carry. Conditions where the OSV is not carrying products covered by the present Code, or is carrying only residues of such products, need not be considered for the purpose of the present Code.

2.5 Flooding assumptions

2.5.1 The provisions of 2.8 should be confirmed by calculations which take into consideration the design characteristics of the vessel; 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.

2.5.2 The permeability of spaces assumed to be damaged should be as follows:

Spaces Permeability
Appropriated to stores 0.60
Occupied by accommodation 0.95
Occupied by machinery 0.85
Voids 0.95
Intended for consumable liquids 0 to 0.95footnote
Intended for other liquids 0 to 0.95footnote
Intended for dry cargo 0.95

2.5.3 Wherever damage penetrates a tank containing liquids it should 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.

2.5.4 Every watertight division within the maximum extent of damage defined in 2.6.1 and 2.6.2 and considered to have sustained damage in positions given in 2.7 should be assumed to be penetrated. Where damage less than the maximum is being considered in accordance with 2.6.3, only watertight divisions or combinations of watertight divisions within the envelope of such lesser damage should be assumed to be penetrated:

  • .1 where a transverse watertight bulkhead is located within the transverse extent of assumed damage and is stepped in way of a double bottom or side tank by more than 3.05 m, the double bottom or side tanks adjacent to the stepped portion of the transverse watertight bulkhead should be considered as flooded simultaneously; and

  • .2 if the distance between the transverse planes passing through the nearest stepped portions of the bulkheads is less than the longitudinal extent of damage given in 2.6.1 and 2.6.2, only one of these bulkheads should be regarded as effective.

2.5.5 The vessel should be so designed as to keep unsymmetrical flooding to the minimum consistent with efficient arrangements.

2.5.6 Equalization arrangements requiring mechanical aids such as valves or cross-levelling pipes, if fitted, should not be considered for the purpose of reducing an angle of heel or attaining the minimum range of residual stability to meet the provisions of 2.8 and sufficient residual stability should 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.

2.5.7 If pipes, ducts, trunks or tunnels are situated within the assumed extent of damage penetration, as defined in 2.6, arrangements should be such that progressive flooding cannot thereby extend to compartments other than those assumed to be flooded for each case of damage.

2.5.8 For vessels subject to 2.6.1 the buoyancy of any superstructure directly above the side damage should 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 provisions of 2.8.2.2 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 2.8; however, the immersion of any other openings capable of being closed weathertight may be permitted.

2.6 Damage assumptions

2.6.1 For vessels carrying more than 1200 m3 of products classified in the IBC Code as requiring type 3 ship or type 2 ship, or more than 150 m3 of products classified in the IBC Code as requiring type 1 ship, the assumed maximum extent of damage should be:

  • .1 Side damage

  • Longitudinal extent Transverse extent Vertical extent
      1/3L2/3 B/5 (measured inboard from the vessel's side at right angles to the centreline at the level of the summer load line) Upwards without limit (measured from the moulded line of the bottom shell plating at centreline)
  • .2 Bottom damage

  • Location of damage Longitudinal extent Transverse extent Vertical extent
    .1 Within 0.3L (measured from the forward perpendicular) 1/3L2/3 B/6 B/15 or 6 m, whichever is less (measured from the moulded line of the bottom shell plating at centreline (see 2.9.2))
    .2 Any other part of the vessel 1/3L2/3 or 5 m, whichever is less B/6 or 5 m, whichever is less B/15 or 6 m, whichever is less (measured from the moulded line of the bottom shell plating at centreline (see 2.9.2)

2.6.2 For vessels carrying not more than 1200 m3 of products classified in the IBC Code as requiring type 3 ship or type 2 ship, and not more than 150 m3 of products classified in the IBC Code as requiring type 1 ship the assumed maximum extent of damage should be:

  • Side damage

  • Vessel length Longitudinal extent Transverse extent Vertical extent
    .1 24≤L≤43 m 0.1L 760 mm (measured inboard from the vessel's side at right angles to the centreline at the level of the summer load line) From the underside of the cargo deck, or continuation thereof, downward for the full depth of the vessel
    .2 43<L<80 m 3 m + 0.03L 760 mm (measured inboard from the vessel's side at right angles to the centreline at the level of the summer load line) From the underside of the cargo deck, or continuation thereof, downward for the full depth of the vessel
    .3 80≤L≤100 m 1/3L2/3 B/20, but not less than 760 mm (measured inboard from the vessel's side at right angles to the centreline at the level of the summer load line) From the underside of the cargo deck, or continuation thereof, downward for the full depth of the vessel
    .4 L>100 m 1/3L2/3 B/15, but not less than 760 mm (measured inboard from the vessel's side at right angles to the centreline at the level of the summer load line) From the underside of the cargo deck, or continuation thereof, downward for the full depth of the vessel

2.6.3 If any damage of a lesser extent than the maximum damage specified in 2.6.1 or 2.6.2 would result in a more severe condition, such damage should be considered.

2.6.4 A transverse watertight bulkhead extending from the vessel's side to a distance inboard not less than the transverse extent of damage indicated in 2.6.2 measured at the level of the summer load line joining longitudinal watertight bulkheads may be considered as a transverse watertight bulkhead for the purpose of the damage calculations in 2.6.2.

2.7 Standard of damage

Vessels should be capable of surviving damage with the assumptions in 2.5 and 2.6 determined by the following standards:

  • .1 a vessel that carries more than 150 m3 of ship type 1 products should be assumed to sustain damage described in 2.6.1 anywhere along the length;

  • .2 a vessel with a length (L) greater than 150 m that carries more than 1200 m3 of ship types 2 and 3 products should be assumed to sustain damage described in 2.6.1 anywhere along the length;

  • .3 a vessel with a length (L) of 150 m or less that carries more than 1200 m3 of ship types 2 and 3 products and not more than 150 m3 of ship type 1 products should be assumed to sustain damage described in 2.6.1 anywhere along the length except involving bulkheads bounding a machinery space of category A;

  • .4 a vessel with a length (L) greater than 100 m that carries 800 m3 or more but not more than 1200 m3 of ship types 2 and 3 products and not more than 150 m3 of ship type 1 products should be assumed to sustain damage described in 2.6.2 anywhere along the length and should also comply with SOLAS regulations II-1/6 to II-1/7-3 (probabilistic damage stability standard for a cargo ship);

  • .5 a vessel with a length (L) of 100 m or less that carries 800 m3 or more but not more than 1200 m3 of ship types 2 and 3 products and not more than 150 m3 of ship type 1 products should be assumed to sustain damage described in 2.6.2 anywhere along the length;

  • .6 a vessel with a length (L) greater than 100 m that carries less than 800 m3 of ship types 2 and 3 products and not more than 150 m3 of ship type 1 products should be assumed to sustain damage described in 2.6.2 anywhere along the length between transverse watertight bulkheads and should also comply with SOLAS regulations II-1/6 to II-1/7-3 (probabilistic damage stability standard for a cargo ship); and

  • .7 a vessel with a length (L) of 100 m or less that carries less than 800 m3 of ship types 2 and 3 products and not more than 150 m3 of ship type 1 products should be assumed to sustain damage described in 2.6.2 anywhere along the length between transverse watertight bulkheads.

2.8 Survival requirements

2.8.1 Vessels subject to the present Code should be capable of surviving the assumed damage specified in 2.6 to the standard provided in 2.7 in a condition of stable equilibrium and should satisfy the following criteria.

2.8.2 For vessels subject to 2.6.1:

  • .1 in any stage of flooding:

    • .1 the waterline, taking into account sinkage, heel and trim, should be below the lower edge of any opening through which progressive flooding or downflooding may take place; such openings should 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 should not exceed 25, except that this angle may be increased to 30 if no deck immersion occurs; and

    • .3 the residual stability during intermediate stages of flooding should never be significantly less than that required by 2.8.2.2;

  • .2 at final equilibrium after flooding:

    • .1 the righting-lever curve should 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 radians. 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 2.8.2.1 and other openings capable of being closed weathertight may be permitted; and

    • .2 the emergency source of power should be capable of operating.

2.8.3 For vessels subject to 2.6.2:

  • .1 the final waterline, taking into account sinkage, heel and trim, should be below the lower edge of any opening through which progressive flooding may take place. Such openings should include air pipes and those which are capable of being closed by means of weathertight doors or hatch covers and 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 in the final stage of flooding, the angle of heel due to unsymmetrical flooding should not exceed 15. This angle may be increased up to 17 if no deck immersion occurs; and

  • .3 the stability in the final stage of flooding should be investigated and may be regarded as sufficient if the righting-lever curve has, at least, a range of 20 beyond the position of equilibrium in association with a maximum residual righting lever of at least 100 mm within this range. Unprotected openings should not become immersed at an angle of heel within the prescribed minimum range of residual stability unless the space in question has been included as a floodable space in calculations for damage stability. Within this range, immersion of any openings referred to in 2.8.3.1 and any other openings capable of being closed weather tight may be authorized.

2.9 Location of cargo tanks

2.9.1 Cargo tanks should be located at the following distances inboard:

  • .1 Cargo tanks for IBC Code ship type 1 products: from the side shell plating, not less than the transverse extent of damage specified in 2.6.1.1.1, and from the moulded line of the bottom shell plating at centreline, not less than the vertical extent of damage specified in 2.6.1.2.1, and nowhere less than 760 mm from the shell plating. This provision does not apply to tanks for diluted slops arising from tank washing.

  • .2 Cargo tanks for IBC Code ship type 2 products: from the moulded line of the bottom shell plating at centreline, not less than the vertical extent of damage specified in 2.6.1.2, and nowhere less than 760 mm from the shell plating. This provision does not apply to tanks for diluted slops arising from tank washing.

  • .3 Cargo tanks for IBC Code ship type 3 products: nowhere less than 760 mm from the shell plating. This provision does not apply to tanks for diluted slops arising from tank washing.

2.9.2 Suction wells installed in cargo tanks for IBC Code ship types 2 and 3 products may protrude below the inner bottom plating 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 should not exceed 350 mm. Suction wells installed in accordance with this paragraph may be ignored in determining the compartments affected by damage.


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