Section
5 Fore and aft end arrangements
5.1 General
5.1.2 The
requirements of this Section apply to the fore and aft ends and relate
to structure situated in the region forward of 0,7L
R and
aft of 0,3L
R respectively.
5.2 Structural continuity
5.2.1 The
Rules provide for both longitudinal and transverse framing systems.
5.2.2 Where
the shell, deck and inner bottom are longitudinally framed in the
midship region, this system of framing is to be carried forward and
aft as far as possible.
5.2.3 End
connections of longitudinals to bulkheads are to provide adequate
fixity, lateral support and as far as practicable, direct continuity
of longitudinal strength, see also
Vol 1, Pt 3, Ch 2, 3 Main hull structure.
5.2.4 Suitable
scarfing arrangements are to be made to ensure continuity of strength
and the avoidance of abrupt structural changes.
5.2.5 Where
longitudinal framing terminates and is replaced by a transverse system,
adequate arrangements are to be made to avoid an abrupt changeover.
Where a forecastle is fitted extending forward from 0,85L
R, longitudinal framing at the upper deck and topsides is generally
to be continued forward of the aft bulkhead of this superstructure.
5.2.6 Where
a superstructure or poop is fitted extending forward of 0,15L
R, longitudinal framing at the upper deck and topsides is generally
to be continued aft of the forward bulkhead of this superstructure.
5.2.7 The
forecastle side plating may be a continuation of the side shell plating
or fitted as a separate assembly. The side plating is to be stiffened
by side frames effectively connected to the deck structure. Deep webs
are to be fitted to ensure overall rigidity.
5.3 Minimum bow height and extent of forecastle
5.3.1 The
requirements regarding minimum bow height given in Vol 1, Pt 3, Ch 2, 5.3 Minimum bow height and extent of forecastle 5.3.2 are to be complied with. Only
in exceptional circumstances and in specialist ships will any relaxation
be given to this requirement where it interferes with the safe operation
of the vessel. In such cases, due consideration is to be given to
the clearing of seawater from the forecastle deck. The effects on
strength and stability are also to be considered.
5.3.2 All
sea-going ships are to be fitted with forecastles, or increased sheer
on the upper deck or equivalent, such that the distance from the waterline
design draught to the top of the exposed deck at side at the F.P.
is not less than:
where
|
C
b
|
= |
block coefficient |
|
L
R
|
= |
Rule length, in m |
|
H
b
|
= |
minimum bow height, in mm |
|
d
1
|
= |
draught at 85 per cent of the depth, D, see
Vol 1, Pt 3, Ch 1, 5.2 Principal particulars 5.2.10.
|
|
C
wf
|
= |
waterplane area coefficient forward of midships
|
|
B
|
= |
moulded
breadth, in m |
|
A
wf
|
= |
is the forward waterplane area at draught d
1,
in m2.
|
5.3.3 Ships
shall have additional reserve of buoyancy in the fore end region to
ensure sufficient longitudinal righting energy to recover from bow
immersion in a seaway and be designed to prevent the excessive shipping
of green seas.
5.3.4 Ships
which are designed to suit exceptional operational requirements, restricted
in their service to service area SA4, or of novel configuration
will be specially considered on the basis of the Rules.
5.3.5 Where
the bow height required in Vol 1, Pt 3, Ch 2, 5.3 Minimum bow height and extent of forecastle 5.3.2 is
obtained by increased sheer, the sheer shall extend for at least 15
per cent of the length of the ship measured abaft the forward end
of L
R. Where it is obtained by fitting a forecastle,
the forecastle shall extend from the stem to a point at least 0,07L
R abaft the forward end of L
R.
5.4 Bow crumple zone
5.4.1 In general
the bow crumple zone is that space forward of the collision bulkhead.
Embarked personnel or crew accommodation and the carriage of fuel,
hazardous materials and other oils are not permitted in the bow crumple
zone.
5.5 Deck structure
5.5.2 The
deck plating thickness and supporting structure are to be suitably
reinforced in way of anchor windlass, other deck machinery, and in
way of cranes, masts or derrick posts, RAS stump masts, and weapon
launching positions, etc.
5.5.3 Where
large openings are arranged at lower decks near the side shell, it
may be necessary to increase the adjacent deck structure to ensure
effective support for side framing.
5.5.4 In NS1
and NS2 ships, on decks aft of the after cutup, deep beams are generally
to be fitted in way of web frames. Deck girders are generally to be
spaced not more than 3,0 m apart and integrated with the primary structure
forward.
5.6 Shell envelope plating and framing
5.6.2 The
thickness and width of plate keels in the forward region are to be
the same as that required in the midship region.
5.6.3 The
scantlings of plate stems are to be determined from Vol 1, Pt 6, Ch 3, 5 Shell envelope plating Plate stems are to be
supported by horizontal diaphragms positioned in line with the side
stringers or perforated flats with intermediate breasthook diaphragms.
Diaphragms are to be spaced not more than 1,5 m apart, measured along
the stem. Where the stem plate radius is large, a centreline stiffener
or web will be required.
5.6.5 The
shell plating may be required to be increased in thickness locally
in way of openings such as hawse pipes and sonar domes, where fitted.
5.6.8 The
bottom longitudinals are to be continuous in way of both watertight
and non-watertight floors.
5.6.9 Where
the shape of the after hull is such that there are large flat areas,
particularly in the vicinity of the propellers, additional primary
supports for the secondary stiffening may be required. Their extent
and scantlings will be specially considered.
5.7 Single and double bottom structure
5.7.2 The
minimum depth of centre girder forward is generally to be the same
as that required in the midship region.
5.7.3 Where
the height of the double bottom varies, structural continuity is to
be maintained. An inner bottom where fitted is to be gradually sloped
over an adequate longitudinal extent. Knuckles in the plating are
to be arranged close to plate floors. Otherwise, suitable scarfing
arrangements are to be made.
5.7.4 For
ships of full form, in fore peak and deep tank spaces, the floors
and bottom transverses are to be supported by a centreline girder
or a centreline wash bulkhead. In other cases the centreline girder
is to be carried as far forward as practicable. The floor panels and
the upper edges of the floors and centreline girder are to be suitably
stiffened.
5.8 Fore peak structure
5.8.1 The
requirements given in this Section apply to the arrangement of primary
structure supporting the fore peak side shell and bulbous bow, the
arrangement of wash bulkheads and perforated flats. The scantlings
of structure in the fore peak is to be in accordance with the relevant
Sections of Vol 1, Pt 6 Hull Construction in Steel.
5.8.2 The
bottom of the peak space is generally to be transversely framed. Longitudinally
framed bottom structure will be specially considered.
5.8.3 Above
the floors, transverse side framing is to be supported by horizontal
side stringers, cross ties and/or perforated flats.
5.8.4 Suitable
transverses or deep beams are to be arranged at the top of the tank
and at perforated flats to provide end rigidity to the side transverses.
5.8.5 Wash
bulkheads are to have an area of perforations not less than five per
cent nor more than 10 per cent of the area of the bulkhead. The plating
is to be suitably stiffened in way of openings. Stiffeners are to
be bracketed at top and bottom.
5.9 Aft peak structure
5.9.1 The
scantlings of aft peak structure are to be as required by the relevant
Sections of Vol 1, Pt 6 Hull Construction in Steel. The plating thickness
is to be increased locally in way of the sterntube gland.
5.9.2 Floors are to be arranged at every frame space and are to be carried to a
suitable height, and at least to above the sterntube, where fitted. Floors are to be
adequately stiffened. In way of propeller shaft brackets, rudder post or rudder horn,
the floors are generally to be carried to the top of the space and are to be of
increased thickness. The extent and amount of the increase will be specially considered,
account being taken of the arrangements proposed.
5.9.3 Above
the floors, transverse side framing is to be supported by horizontal
stringers, cross ties and/or perforated flats.
5.9.4 Suitable
transverses or deep beams are to be arranged at the top of the tank
to provide end rigidity to the side transverses.
5.9.5 A centreline
wash bulkhead is to be arranged in the upper part of the aft peak
space. Additional wash bulkheads are to be fitted port and starboard
where the width of the tank exceeds 20 m.
5.9.6 The
plating is to be suitably stiffened in way of openings, and the arrangement
of openings is to be such as to maintain adequate shear rigidity.
5.9.8 Centre
and side girders where fitted are to be bracketed to the transom framing
members by substantial knees. Hard spots are to be avoided in way
of the end connections and care is to be taken to ensure that the
stiffening member to which the transom knee is attached can satisfactorily
carry the load.
5.10 Bulbous bows
5.10.1 Where
a bulbous bow is fitted, the structural arrangements are to be such
that the bulb is adequately supported and integrated into the fore
peak structure.
5.10.2 At
the fore end of the bulb the structure is generally to be supported
by horizontal diaphragm plates spaced generally 1,0 m apart in conjunction
with a deep centreline web.
5.10.3 In
general, vertical transverse diaphragm plates are to be arranged in
way of the transition from the peak framing to the bulb framing.
5.10.4 In
way of a wide bulb, additional strengthening in the form of a centreline
wash bulkhead is generally to be fitted.
5.10.5 In
way of a long bulb, additional strengthening in the form of transverse
wash bulkheads or substantial web frames spaced about five frame spaces
apart are generally to be fitted.
5.10.6 The
shell plating is to be increased in thickness at the fore end of the
bulb and in other areas likely to be damaged by the anchors and chain
cables. The increased plate thickness is to be the same as that required
for plated stems.
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