Section
6 Machinery space arrangements
6.1 General
6.1.1 Requirements
particular to machinery spaces, including protected machinery casings
and engine seatings only, are given in this Section. For other scantlings
and arrangement requirements, see the relevant section
in this Chapter.
6.2 Structural configuration
6.2.1 Requirements
are given for ships constructed using either a transverse or longitudinal
framing system, or a combination of the two.
6.2.2 Machinery
space stiffening is generally to be arranged in the same manner as
structure immediately forward and aft of the space. For NS1 and NS2
ships this will generally be longitudinal. Machinery spaces adjacent
to the aft peak bulkhead may be constructed using a transverse framing
system or a combination of longitudinal and transverse.
6.3 Structural continuity
6.3.1 Suitable
scarfing arrangements are to be made to ensure continuity of strength
and the avoidance of abrupt discontinuities where structure which
contributes to the main longitudinal strength of the ship is omitted
in way of a machinery space.
6.3.2 Where
the longitudinal framing terminates and is replaced by transverse
framing, a suitable scarfing arrangement of the longitudinal framing
is to be arranged.
6.4 Deck structure
6.4.1 The
corners of machinery space openings are to be of suitable shape and
design to minimise stress concentrations.
6.4.2 Where
a transverse framing system is adopted, deck beams are to be supported
by a suitable arrangement of longitudinal girders in association with
pillars or pillar bulkheads. Deep beams are to be arranged in way
of the ends of engine casings and also in line with side web frames
where fitted.
6.4.3 Where
a longitudinal framing system is adopted, deck longitudinals are to
be supported by deck transverses in association with pillars or pillar
bulkheads. The maximum spacing of transverses is given in Vol 1, Pt 3, Ch 2, 6.5 Side shell structure 6.5.2. Deck transverses are to be
in line with side transverses or web frames.
6.4.5 The
scantlings of lower decks or flats are generally to be as given in Vol 1, Pt 6, Ch 3, 10 Deck structures. However, in way of concentrated
loads such as those from boiler bearers or heavy auxiliary machinery,
etc. the scantlings of deck structure will be specially considered,
taking account of the actual loading.
6.4.6 In way
of machinery space openings, etc. particularly towards the aft end,
decks or flats are to have sufficient strength where they are intended
to provide effective primary support to side framing, webs or transverses.
6.4.7 Where
decks terminate at a machinery space bulkhead, suitable scarfing arrangements
are to be arranged. The side shell of the machinery space is generally
to be supported by a stringer at deck level. The stringer can be either
fully effective or acting as part of a grillage. Bulkhead stiffeners
at the deck level are to be supported against tripping.
6.5 Side shell structure
6.5.1 The
side shell structure of machinery spaces is to be effectively supported
by a system of primary framing with web frames and stringers. General
requirements for web frames are given in this Section for both longitudinal
and transverse framing systems.
6.5.2 The
maximum spacing of side shell transverses in longitudinally framed
machinery spaces is generally not to exceed 2,5 m in NS1 and NS2 ships,
and 1,5 m in NS3 ships.
6.5.3 The
maximum spacing of side shell web frames in transversely framed machinery
spaces is generally not to exceed five frame spaces. They are to extend
from the tank top to the level of the lowest deck above the design
waterline.
6.5.4 The
maximum spacing of stringers is generally not to exceed 3,0 m.
6.6 Double and single bottom structure
6.6.2 In the
bottom structure sufficient fore and aft girders are to be arranged
in way of the main machinery to effectively distribute its weight
and to ensure adequate rigidity of the structure. In midship machinery
spaces these girders are to extend for the full length of the space
and are to be carried aft to support the foremost shaft tunnel bearing.
This extension beyond the after bulkhead of the machinery space is
to be for at least three transverse frame spaces, aft of which the
girders are to scarf into the structure. Forward of the forward machinery
space bulkhead, the girders are to be tapered off over three frame
spaces and effectively scarfed into the structure. In machinery spaces
in the aft end of the ship the girders are to be carried as far aft
as practicable and the ends effectively supported by web frames or
transverses. Care is to be taken to avoid any abrupt changes or discontinuities.
6.6.3 Where,
in NS3 ships, the bottom is transversely framed, plate floors are
to be fitted at every frame in the machinery space and under the main
machinery, rafts, seatings and thrust bearing.
6.6.4 Where
the bottom is longitudinally framed, plate floors are to be fitted
at a maximum spacing of 2,5 m in NS1 and NS2 ships, and 1,5 m in NS3
ships in the machinery space under the main machinery, rafts, seatings
and thrust bearing.
6.6.5 The
minimum depth of the centre girder and its thickness are to be at
least the same as required in way of other spaces amidships. Where
the height of inner bottom in the machinery spaces differs from that
in adjacent spaces, continuity of longitudinal material is to be maintained.
In ships with a double bottom it is to be achieved by sloping the
inner bottom over an adequate longitudinal extent. The knuckles in
the plating are to be arranged close to plate floors.
6.6.6 Margin
plates and drainage wells are to be provided as necessary and will
be subject to special consideration.
6.6.7 Suitable
arrangements are to be made to provide free passage of water from
all parts of the bilge to the pump suctions. General requirements
are given in Vol 1, Pt 3, Ch 2, 3.1 General 3.1.18.
6.6.9 Where
practicable, side girders outboard of the engines are to be fitted
and are to line up with the side girders in adjacent spaces.
6.7 Machinery casings
6.7.2 Where
casing sides act as girders supporting decks over, care is to be taken
that access openings do not seriously weaken the structure. Openings
are to be effectively framed and reinforced if necessary. Particular
care is to be paid to stiffening where the casing supports the funnel
or exhaust uptakes.
6.7.3 Machinery
casings are to be supported by a suitable arrangement of deep beams
or transverses and longitudinal girders in association with pillars
or pillar bulkheads. In way of particularly large machinery casing
openings, cross ties may be required, and these are to be arranged
in line with deep beams or transverses. Where casing stiffeners carry
loads from deck transverses, girders, etc. or where they are in line
with pillars below, they are to be suitably reinforced.
6.7.4 Casing
bulkheads are to be made gastight and the access doors are to be of
a gastight self-closing type.
6.8 Integral fuel tanks
6.9 Machinery seatings
6.9.2 This
section applies to machinery or machinery raft seatings that are directly
supported by the ship’s hull. They are to be effectively secured
to the hull and to be of adequate scantlings to resist the various
gravitational, thrust, torque, dynamic and vibratory forces which
may be imposed on them. Due attention is to be paid to the stiffness
requirements of the machinery or raft supported.
6.9.3 Seatings
are to be of substantial construction and efficiently supported by
transverse and horizontal brackets or gusset plates. These should
generally be arranged in line with plate floors and girders in a double
bottom or with suitable deep beams or transverses and girders at upper
decks. Where applicable, seats are to be designed to ensure proper
alignment with gearing and allow for thermal expansion effects.
6.9.4 In general
seats are not to be arranged in way of breaks or recesses in the bottom
structure.
6.9.5 Main
machinery or raft holding-down bolts are to be arranged as near as
practicable to floors and longitudinal girders. When this cannot be
achieved, additional floors are to be fitted.
6.9.6 Auxiliary
machinery is to be secured on seating of adequate scantlings, so arranged
as to distribute the loadings evenly into the supporting structure.
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