Section 1 General

1.1.1 This Chapter illustrates the general principles to be adopted in the design of naval ships. Principles for subdivision and for maintaining watertight integrity are also covered.

1.1.2 Where additional requirements relating to particular ship types apply, these requirements are indicated in the appropriate Parts and are to be complied with as necessary.

1.1.3 These Rules are to be applied with reference to the operational conditions defined in the Concept of Operations, see Vol 1, Pt 1, Ch 2, 2.2 Definitions.

1.2.1 The Down flooding angle is the least angle of heel at which openings in the hull, superstructure or deckhouses, which cannot be closed weathertight, immerse and allow flooding to occur.

1.2.2 The minimum required angle of down flooding, θ_df, is to be taken as 40° except when a higher minimum angle is required in accordance with the specified subdivision and stability standard(s), see Vol 1, Pt 1, Ch 2, 1.1 Framework of Classification 1.1.9

1.2.3 The vertical limit of watertight integrity is the vertical extent to which water might rise in the damaged condition and below which structures and systems forming sub-division boundaries must be watertight, see Vol 1, Pt 3, Ch 2, 1.3 Watertight and weathertight integrity 1.3.6

1.3.1 The extents of the external and internal watertight and weathertight integrity are defined by the intact and damage stability requirements, see Vol 1, Pt 1, Ch 2, 1.1 Framework of Classification 1.1.9. From these extents, the design pressure heads for bulkheads and other boundaries can be derived as well as the closing arrangement requirements for openings. Weathertight and watertight integrity are defined in Vol 1, Pt 3, Ch 1, 5 Definitions and see Vol 1, Pt 3, Ch 4 Closing Arrangements and Outfit for the requirements for closing arrangements.

1.3.2  Intact stability

1.3.3 Intact stability calculations to satisfy the applicable criteria may be based on the buoyancy of the main hull, together with any superstructures that have watertight and weathertight boundaries, see Figure 2.1.1 and Figure 2.1.2 .

Figure 2.1.1

Figure 2.1.2

1.3.4 Doors, hatches, ventilators, windows, sidelights, etc. provided with closing appliances which can be secured weathertight, and small openings through which progressive flooding cannot take place are not considered as down flooding points.

1.3.5 If the angle of down flooding is less than θ_df, see Vol 1, Pt 3, Ch 2, 1.2 Definitions 1.2.2, with the ship at its design draught, it is necessary to establish whether there is sufficient area under the righting lever curve up to the angle of down flooding. If there is insufficient area, then the opening which is causing down flooding to occur is to be provided with a weathertight closing appliance, or be repositioned.

1.3.6  Damage stability

1.3.7 Typically there are two approaches to defining the limits of watertight and weathertight integrity:

1. One where the watertight integrity is defined by the bulkhead or freeboard deck, in accordance with normal SOLAS - International Convention for the Safety of Life at Sea requirements.

2. The other is based on watertight integrity up to a damaged stability draught and heel envelope, and more commonly used by navies.

These two approaches are illustrated in Figure 2.1.1 and Figure 2.1.2 respectively.

1.3.8  Figure 2.1.1 represents the SOLAS - International Convention for the Safety of Life at Sea style requirements.

• Below the limit of watertight integrity the boundary structure is to be watertight.
• Below the limit of weathertight integrity defined by the transient roll angle the boundary structure is to be weathertight, in order to prevent ingress of water into the enclosed volume considered buoyant in the stability calculations and prevent downflooding.
• Above the limit of weathertight integrity the boundary structure, or some other internal boundary, may need to be gas-tight for CBRN protection.
• Below the limit of watertight integrity defined by the top of the watertight bulkhead, the bulkhead is to be designed as watertight.
• Below the limit of weathertight integrity defined by the transient roll angle and above the limit of watertight integrity the internal structure is to be designed to prevent progressive flooding of water into other compartments.

1.3.9  Figure 2.1.2 represents a standard based on the damaged stability draught and heel envelope approach commonly used by navies.

• Below the limit of watertight integrity the boundary structure is to be watertight.
• Below the limit of weathertight integrity defined by the transient roll angle the boundary structure is to be weathertight.
• Above the limit of weathertight integrity the boundary structure, or some other internal boundary, may need to be gastight for CBRN protection.
• Below the limit of watertight integrity defined by the locii of static damage waterlines the watertight bulkheads are to be designed as watertight.
• Below the limit of weathertight integrity defined by the transient roll angle and above the limit of watertight integrity the internal structure is to be weathertight in order to prevent progressive flooding of water into other compartments.

1.3.10 In the absence of specific information on the vertical limit of watertight integrity, the upper extent of the watertight boundary may be assumed with the apex of the triangle on the damage control deck at the location under consideration, see Figure 2.1.2 and Vol 1, Pt 3, Ch 1, 5.4 Decks 5.4.4.

1.4.1 The role and duty of a naval ship dictates that a certain degree of structural redundancy should be incorporated in the design. It is recommended that, as a minimum standard, a basic level of structural redundancy is included where practicable. This is normally achieved by considering likely damage scenarios, identifying the effects on structure, assessing the new loads and ensuring that the remaining structure will be satisfactory.

1.4.2 These Rules will not automatically ensure that a ship has structural redundancy. It is the responsibility of the designer to consider and design for the possible loads on a structure from damage scenarios. The RSA notation can be used to define residual strength requirements.

1.4.3 At a very basic level structural redundancy can be achieved by considering the removal of appropriate items of structure and re-evaluating the strength of remaining members using the loads presented in these Rules. Alternatively, the overall structural redundancy can be formally assessed and a notation assigned using the residual strength analysis detailed in Vol 1, Pt 3, Ch 2, 1.5 Residual Strength Assessment, RSA.

1.5.1 The design of a naval ship necessitates the reliable evaluation of its structural vulnerability to ensure the existence of adequate residual strength in the event of structural damage following a contact/collision incident or as a result of wartime activities. This strength assessment is additional to that required to cope with the design bending moments derived from environmental sea-state loading. The RSA notation within the Rules may be used to formally assess the overall structural redundancy.

1.5.2 The Owner may specify that a residual strength assessment is not required. In this case, the residual strength notation and all other notations which require the residual strength notation will not be assigned.

1.5.3 The capability to survive is to be judged on the residual structural strength after damage being able to meet specified global strength requirements and also local strength requirements in the event of damage leading to flooding, see Vol 1, Pt 6, Ch 4, 4 Residual Strength Assessment, RSA.

1.5.4 A residual strength assessment performed as defined in the Rules assumes that a ship can remain operational for a limited period of time in reduced sea states, see Vol 1, Pt 6, Ch 4, 1.2 Hull girder strength notations. Where a higher operational capability following damage is specified, special consideration will need to be given and revised criteria set.

1.5.5 The Owner may specify an alternative mission statement, in which case the requirements of the residual strength assessment procedure will be modified.

1.5.6 The residual strength assessment as defined in the Rules considers three main definitions of damage:

• Peacetime damage extents, see Vol 1, Pt 6, Ch 4, 2 Hull girder strength.
• Military threats, see Vol 1, Pt 4, Ch 2, 7 Residual strength
• As defined by the Owner.

1.5.7 The environmental parameters for the residual strength assessment procedure are given inVol 1, Pt 5, Ch 2 Environmental Conditions. The local and global loads for use in the RSA assessment procedure are given in Vol 1, Pt 5, Ch 3, 5 Local design loads for decks and bulkheads and Vol 1, Pt 5, Ch 4, 5 Residual strength hull girder loads respectively.

1.5.8  RSA notation assessment levels are given in Vol 1, Pt 4, Ch 2, 7 Residual strength. The acceptance criteria and procedures to be adopted for the application of the residual strength notation are given in Vol 1, Pt 6, Ch 4, 4 Residual Strength Assessment, RSA. See also Vol 1, Pt 1, Ch 2, 3.6 Service area notations 3.6.1.

1.5.9 Further guidance for undertaking residual strength analysis for the determination of a residual strength notation is given in LR's Naval Ship Guidance Notes.