7 Extents of Damage Considered
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Statutory Documents - IMO Publications and Documents - Circulars - Maritime Safety Committee - MSC.1/Circular.1461 – Guidelines for Verification of Damage Stability Requirements for Tankers – (08 July 2013) - Annex – Guidelines for Verification of Damage Stability Requirements for Tankers - Part 1 – Guidelines for Preparation and Approval of Tanker Damage Stability CalculationsGuideline for scope of damage stability verification on new oil tankers, chemical tankers and gas carriers1 - 7 Extents of Damage Considered

7 Extents of Damage Considered

Parent topic: Part 1 – Guidelines for Preparation and Approval of Tanker Damage Stability CalculationsGuideline for scope of damage stability verification on new oil tankers, chemical tankers and gas carriers footnote

7.1 Maximum extents

 The following provisions regarding the maximum extent and the character of the assumed damage should be applied:

Table 3

.1 Side damage: MARPOL/IBC/IGC ICLL (Type A ships)
.1.1 Longitudinal extent: 1/3 L2/3 or 14.5 m, whichever is less Single compartment between adjacent transverse bulkheads as specified in ICLL paragraph 12(d) 1)
.1.2 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) B/5 or 11.5, whichever is the lesser (measured inboard from the side of the ship perpendicularly to the centreline at the level of the summer load waterline) 1)
.1.3 Vertical extent: upwards without limit (measured from the moulded line of the bottom shell plating at centreline) From baseline upwards without limit
.2 Bottom damage 2) : MARPOL/IBC/IGC
For 0.3 L from the forward perpendicular of the ship Any other part of the ship
.2.1 Longitudinal extent: 1/3 L2/3 or 14.5 m, whichever is less 1/3 L2/3 or 5 m, whichever is less
.2.2 Transverse extent: B/6 or 10 m, whichever is less B/6 or 5 m, whichever is less
.2.3 Vertical extent: MARPOL/IBC:
B/15 or 6 m, whichever is less (measured from the moulded line of the bottom shell plating at centreline) 		MARPOL/IBC:
B/15 or 6 m, whichever is less (measured from the moulded line of the bottom shell plating at centreline)
IGC:
B/15 or 2 m, whichever is less (measured from the moulded line of the bottom shell plating at centreline) 		IGC:
B/15 or 2 m, whichever is less (measured from the moulded line of the bottom shell plating at centreline)
.3 Bottom raking damage 3) : MARPOL
.3.1 Longitudinal extent: in tankers of 75,000 tonnes deadweight and above:
0.6 L(m) measured from the forward perpendicular of the ship
in tankers of less than 75,000 tonnes deadweight:
0.4 L(m) measured from the forward perpendicular of the ship
.3.2 Transverse extent: B/3 anywhere in the bottom
.3.3 Vertical extent: Breach of the outer hull
1) See appendix 3.
2) Bottom damage is not required in the ICLL.
3) Bottom raking damage is required only for oil tankers of 20,000 tonnes deadweight and above.

7.2 Lesser extents

  7.2.1 If any damage of a lesser extent than the maximum damage specified in table 3 would result in a more severe condition, such damage should be considered (see section 4.5.4).

  7.2.2 In the case of a gas carrier, local side damage anywhere in the cargo area extending inboard 760 mm measured normal to the hull shell should be considered, and transverse bulkheads should be assumed damaged when also required by the applicable subparagraphs of section 2.8.1 of the IGC Code.

7.3 Rationale for reviewing lesser extents including symmetrical vs. unsymmetrical tank arrangement/geometry – Calculation on weakest side

  7.3.1 For a given loading condition, the following examples of damages of a lesser extent may result in a more severe situation than that caused by the maximum damage specified in table 3:

  • .1 Example of damage on double bottom tanks with watertight centre girder:

    • .1 Damage of a lesser extent which could occur at the bottom plate of the ship, without damaging the centre girder, will lead to flooding of the double bottom tank on one side of the ship only. This is the case of unsymmetrical flooding. For the same location, damage of a maximum extent would cause damage on the centre girder and therefore flooding of the double bottom tanks on both sides. This is the case of symmetrical flooding (see appendix 4).

    • .2 Compared to the symmetrical flooding in the case of maximum damage extent, unsymmetrical flooding of spaces, caused by damage of a lesser extent might lead to a more severe situation. Of course, in case of non-watertight centre girder, the effect of damage of lesser and maximum extent would be the same.

  • .2 Example of damage with lesser vertical extents:
    Damage starting from above a tank top would flood the spaces only above the double bottom (see appendix 4). This may result in a more onerous residual stability or heeling angle.

  7.3.2 Taking into account the above examples, it is necessary to review damages of lesser extents considering the symmetrical or unsymmetrical nature of tank arrangements of the ship and geometry of the ship. The ship's damage stability is to be ensured, in the most severe or weakest case of damage of lesser extents.

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