Section
1 General
1.1 Application
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.
1.2 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.
1.3 Watertight and weathertight integrity
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.
1.3.3 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 θdf, 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.
1.3.7 Typically
there are two approaches to defining the limits of watertight and
weathertight integrity:
-
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.
-
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 Structural redundancy
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 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:
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.
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