Section 4 Machinery space
4.1 Symbols
4.1.1 The symbols used in this Chapter are defined as follows:
L |
= |
Rule length in metres |
L2
|
= |
Rule length, L, but need not be taken greater than 300
m |
σyd |
= |
specified minimum yield stress of the material, in
N/mm2
|
s |
= |
stiffener spacing, in mm. |
4.2 General
4.2.1
Application.
- This Section prescribes scantling requirements for a machinery
space or spaces located at any longitudinal frame location, such as a machinery
space at the forward end. The requirements of this Section apply to all
machinery spaces, regardless of location. For conventional self-propelled
vessels, the requirements of Pt 3, Ch 7 Machinery Spaces of the Rules for Ships may also be
used for guidance.
- Where a machinery space is permitted to overlap either of the
regions defined in Pt 10, Ch 3, 3 Forward of the forward cargo tank and Pt 10, Ch 3, 5 Aft end, the most onerous of the design requirements
for the machinery space and the overlapping region are to take precedence.
- Where a machinery space is located at a forward or aft region
susceptible to local impact and slamming loads, the additional strengthening
requirements prescribed in Pt 10, Ch 3, 6 Evaluation of structure for sloshing and impact loads are to be complied with in addition to
the requirements in this Section.
4.2.2
Arrangements.
- All machinery and related systems are to be supported to
distribute the loads into the structure of the ship unit. The adjacent
structure is to be suitably stiffened.
- Primary support members are to be positioned giving consideration
to the provision of through stiffeners and in-line pillar supports to achieve
an efficient structural design.
- The scantlings of the structure and the area of attachments are
to consider the weight, power and proportions of the machinery, especially
where the engines are positioned relatively high in proportion to the width of
the bed plate.
- The foundations for main machinery and, where fitted, propulsion
units, reduction gears, shaft and thrust bearings, and the structure supporting
those foundations are to maintain the required alignment and rigidity under all
anticipated conditions of loading. It is recommended that plans of the above
structure be submitted to the machinery manufacturer for review.
- A cofferdam is to be provided to separate the cargo tanks from
the machinery space. Pump-room, ballast tanks, or fuel oil tanks may be
considered as cofferdams for this purpose.
- When main auxiliary machinery is fitted above the weather deck,
the machinery is to be protected by deckhouses, in accordance with Pt 10, Ch 1, 10.1 General 10.1.1.
4.2.3
Minimum thickness.
- In addition to the requirements for thickness, section modulus and
shear area, as given in Pt 10, Ch 3, 4.3 Bottom structure to Pt 10, Ch 3, 4.9 Scantling requirements, the thickness of plating and stiffeners in
the machinery space is to comply with applicable minimum thickness requirements
for the cargo region given in Pt 10, Ch 3, 2.2 General 2.2.4 and Pt 10, Ch 3, 2.2 General 2.2.5, except as applicable in Pt 10, Ch 3, 4.2 General 4.2.3.
Table 3.4.1 Minimum net thickness
of structure in the machinery space
Scantling location
|
Net thickness
(mm)
|
Plating
|
Lower decks and
flats
|
3,3 +
0,0067s
|
Inner bottom
|
6,5 +
0,02L2
|
Floors and bottom longitudinal girders off
centreline
|
5,5 +
0,02L2
|
Web plating of primary support members
|
5,5 +
0,015L2
|
4.3 Bottom structure
4.3.1
General
- In general, a double bottom is to be fitted in the machinery
space. The depth of the double bottom is to be at least the same as required in
the cargo tank region. Where the depth of the double bottom in the machinery
space differs from that in the adjacent spaces, continuity of the longitudinal
material is to be maintained by sloping the inner bottom over a suitable
longitudinal extent. Lesser double bottom height may be accepted in local
areas, provided that the overall strength of the double bottom structure is not
thereby impaired.
4.3.4
Girders and floors.
- The double bottom is to be arranged with a centreline girder.
- Full depth bottom girders are to be arranged in way of the main
machinery to distribute its weight effectively and to ensure rigidity of the
structure. The girders are to be carried as far forward and aft as practicable,
and be suitably supported at their ends to provide distribution of loads from
the machinery. The girders are to be tapered beyond their required extent.
- Where the bottom is transversely framed, plate floors are to be
fitted at every frame.
- Where the bottom is longitudinally framed, plate floors are to be
fitted at every frame under the main engine and thrust bearing. Outboard of the
engine and bearing seatings, the floors may be fitted at alternate frames.
- Where heavy equipment is mounted directly on the inner bottom,
the thickness of the floors and girders is to be suitably increased.
4.3.5
Inner bottom plating.
- Where main engines or thrust bearings are bolted directly to the
inner bottom, the net thickness of the inner bottom plating is to be at least
19 mm. Hold-down bolts are to be arranged as close as possible to floors and
longitudinal girders. Plating thickness and the arrangements of hold-down bolts
are also to consider the manufacturer’s recommendations.
4.3.6
Sea chests
- Where the inner bottom or double bottom structure forms part of a
sea chest, the thickness of the plating is not to be less than that required
for the shell at the same location, taking into account the maximum unsupported
width of the plating.
4.4 Side structure
4.4.1
General.
- The scantlings of the side shell plating and longitudinals are to
be properly tapered from the midship region towards the aft end.
- A suitable scarphing arrangement of the longitudinal framing is
to be arranged where the longitudinal framing terminates and is replaced by
transverse framing.
- Stiffeners and primary support members are to be supported at
their ends.
4.4.3
Side shell local support members.
- The section modulus and thickness of side longitudinal and
vertical stiffeners are to comply with the requirements in Pt 10, Ch 3, 4.9 Scantling requirements 4.9.1 andPt 10, Ch 3, 4.9 Scantling requirements 4.9.1.
- End connections of longitudinals at transverse bulkheads are to
provide fixity, lateral support, and, when not continuous, are to be provided
with soft-nosed brackets. Brackets lapped onto the longitudinals are not to be
fitted.
4.4.4
Side shell primary support members.
- Web frames are to be connected at the top and bottom to members
of suitable stiffness, and supported by deck transverses.
- The spacing of web frames in way of transversely framed machinery
spaces is generally not to exceed five transverse frame spaces.
- The section modulus and shear area of primary support members are
to comply with the requirements in Pt 10, Ch 3, 4.9 Scantling requirements 4.9.2.
- The web depth is to be not less than 2,5 times the web depth of
the adjacent frames if the slots are not closed.
- Web plating of primary support members is to have a depth of not
less than 14 per cent of the unsupported span in bending.
4.5 Deck structure
4.5.1
General.
- All openings are to be framed. Attention is to be paid to
structural continuity. Abrupt changes of shape, section or plate thickness are
to be avoided.
- The corners of the machinery space openings are to be of suitable
shape and design to minimise stress concentrations.
- In way of machinery openings, deck or flats are to have sufficient
strength where they are intended as effective supports for side transverse
frames or web frames.
- Where a transverse framing system is adopted, deck stiffeners are
to be supported by a suitable arrangement of longitudinal girders in
association with pillars or pillar bulkheads. Where fitted, deck transverses
are to be arranged in line with web frames to provide end fixity and transverse
continuity of strength.
- Where a longitudinal framing system is adopted, deck
longitudinals are to be supported by deck transverses in line with web frames
in association with pillars or pillar bulkheads.
- Machinery casings are to be supported by a suitable arrangement of
deck transverses and longitudinal girders in association with pillars or pillar
bulkheads. In way of particularly large machinery casing openings, cross ties
may be required. These are to be arranged in line with deck transverses.
- The structural scantlings are not to be less than the requirement
for tank boundaries if the deck forms the boundary of a tank.
- The structural scantlings are not to be less than the requirement
for watertight bulkheads if the deck forms the boundary of a watertight
space.
4.5.2
Deck scantlings.
- The plate thickness of deck plating is to comply with the
requirements in Pt 10, Ch 3, 4.9 Scantling requirements 4.9.1.
- The section modulus and thickness of deck stiffeners are to
comply with the requirements in Pt 10, Ch 3, 4.9 Scantling requirements 4.9.1 and Pt 10, Ch 3, 4.9 Scantling requirements 4.9.1.
- The web depth of deck stiffeners is to be not less than 60
mm.
- The section modulus and shear area of primary support members are
to comply with the requirements in Pt 10, Ch 3, 4.9 Scantling requirements 4.9.2.
- The web depth of primary support members is not to be less than 10
per cent and 7 per cent of the unsupported span in bending in tanks and in dry
spaces, respectively, and is not to be less than 2,5 times the depth of the
slots if the slots are not closed. In the case of a grillage structure, the
unsupported span is the distance between connections to other primary support
members.
- In way of concentrated loads from heavy equipment, the scantlings
of the deck structure are to be determined based on the actual loading.
4.5.3
Pillars.
- Pillars are to comply with the requirements of Pt 10, Ch 3, 3.5 Deck structure 3.5.4.
- In double bottoms under widely spaced pillars, the connections of
the floors to the girders, and of the floors and girders to the inner bottom,
are to be suitably increased. Where pillars are not directly above the
intersection of plate floors and girders, partial floors and intercostals are
to be fitted as necessary to support the pillars. Manholes are not to be cut in
the floors and girders below the heels of pillars.
4.6 Machinery foundations
4.6.1
General.
- Main engines and thrust bearings are to be effectively secured to
the hull structure by foundations of sufficient strength to resist the various
gravitational, thrust, torque, dynamic, and vibratory forces which may be
imposed on them.
- In the case of higher power internal combustion engines or
turbine installations, the foundations are generally to be integral with the
double bottom structure. Consideration is to be given to increase substantially
the inner bottom plating thickness in way of the engine foundation plate or the
turbine gear case, and the thrust bearing.
- For ship units with open floors in the machinery space, the
foundations are generally to be arranged above the level of the top of the
floors and securely bracketed.
4.6.2
Foundations for internal combustion engines and thrust bearings.
- In determining the scantlings of foundations for internal
combustion engines and thrust bearings, consideration is to be given to the
general rigidity of the engine and to its design characteristics with regard to
out of balance forces.
- Generally, two girders are to be fitted in way of the foundation
for internal combustion engines and thrust bearings.
NOTE
In general, the gross thickness of foundation top plates is not
to be less than 45 mm, where the maximum continuous output of the propulsion
machinery is 3500 kW or greater.
4.6.3
Auxiliary foundations.
- Auxiliary machinery is to be secured on foundations that are of
suitable size and arrangement to distribute the loads from the machinery evenly
into the supporting structure.
4.7 Tank bulkheads
4.7.1
General.
- Tanks are to comply with the requirements of Pt 10, Ch 3, 3.6 Tank bulkheads, with scantlings determined
using the factors from Pt 10, Ch 3, 4.7 Tank bulkheads 4.7.1 and Pt 10, Ch 3, 4.7 Tank bulkheads 4.7.1.
Table 3.4.2 Permissible bending
stress coefficient for plating
Acceptance criteria
set
|
Structural member
|
βa
|
αa
|
Ca-max
|
AC1
|
Longitudinal
strength members
|
Longitudinally stiffened
plating
|
0,9
|
0,5
|
0,8
|
Transversely or
vertically stiffened plating
|
0,9
|
1,0
|
0,8
|
Other members
|
0,8
|
0
|
0,8
|
AC2
|
Longitudinal
strength members
|
Longitudinally stiffened
plating
|
1,05
|
0,5
|
0,95
|
Transversely or vertically
stiffened plating
|
1,05
|
1,0
|
0,95
|
Other members, including watertight boundary plating
|
1,0
|
0
|
1,0
|
AC3
|
All members
|
1,0
|
0
|
1,0
|
The permissible bending stress coefficient, Ca
, for the design load set being considered is to be taken
as:
|
Ca
|
= |
but not to be taken greater than
Ca-max
|
|
σhg
|
= |
hull girder bending stress for the design
load set being considered and calculated at the load
calculation point |
= |
N/mm2
|
Mv-total
|
= |
design vertical bending moment at the
longitudinal position under consideration for the
design load set being considered, in kNm. The still
water bending moment, Msw-perm
, is to be taken with the same sign as the
simultaneously acting wave bending moment,
Mwv
, see Table 2.6.1 in Chapter 2 |
Iv-net50
|
= |
net vertical hull girder moment of
inertia, at the longitudinal position being considered,
in m4
|
z
|
= |
vertical coordinate of the load
calculation point under consideration, in metres |
zNA-net50
|
= |
distance from the baseline to the
horizontal neutral axis, in metres |
|
Table 3.4.3 Permissible bending
stress coefficient for stiffeners
The permissible bending stress coefficient Cs
is to be taken as:
|
Sign of hull girder bending stress, σhg
|
Side that pressure is acting
on
|
Acceptance criteria
|
Tension (+ve)
|
Stiffener side
|
but not to be taken greater than
Cs-max
|
Compression (–ve)
|
Plate side
|
Tension (+ve)
|
Plate side
|
Cs
=Cs-max
|
Compression (–ve)
|
Stiffener side
|
where
βs, αs,
Cs-max
|
= |
permissible bending stress factors and are
to be taken as: |
|
Acceptance criteria set
|
Structural member
|
βs
|
αs
|
Cs-max
|
AC1
|
Longitudinally effective stiffeners
|
0,85
|
1,0
|
0,75
|
Other stiffeners
|
0,75
|
0
|
0,75
|
AC2
|
Longitudinally effective stiffeners
|
1,0
|
1,0
|
0,9
|
Other stiffeners
|
0,9
|
0
|
0,9
|
Watertight boundary stiffeners
|
0,9
|
0
|
0,9
|
AC3
|
All members
|
1,0
|
0
|
1,0
|
σhg
|
= |
hull girder bending stress for the design
load set being considered and calculated at the
reference point |
|
= |
N/mm2
|
|
Stiffener location
|
Msw-perm
|
Pressure acting on plate
side
|
Pressure acting on stiffener
side
|
Above neutral axis
|
Sagging SWBM
|
Hogging SWBM
|
Below neutral axis
|
Hogging SWBM
|
Hogging SWBM
|
Iv-net50
|
= |
net vertical hull girder moment of
inertia, at the longitudinal position being considered,
in m4
|
z
|
= |
vertical coordinate of the reference
point, in metres |
zNA-net50
|
= |
distance from the baseline to the
horizontal neutral axis, in metres |
|
4.8 Watertight boundaries
4.9 Scantling requirements
4.9.1
Plating and local support members.
- For plating subjected to lateral pressure, the
net plating thickness is to comply with the requirements of Pt 10, Ch 3, 2.3 Hull envelope plating 2.3.2, where Ca
is taken as given in Pt 10, Ch 3, 4.7 Tank bulkheads 4.7.1.
- For stiffeners subjected to lateral pressure,
the net section modulus requirement is to comply with the requirements of Pt 10, Ch 3, 2.4 Hull envelope framing 2.4.2, where Cs
is taken as defined in Pt 10, Ch 3, 4.7 Tank bulkheads 4.7.1.
- For stiffeners subjected to lateral pressure,
the net web thickness based on shear area requirements is to comply with the
requirements of Pt 10, Ch 3, 2.4 Hull envelope framing 2.4.2, where Ct
is taken as given in Pt 10, Ch 3, 3.11 Scantling requirements 3.11.2 in the previous Section.
4.9.2
Primary support members.
- For primary support members intersecting with or in way of curved
hull sections, the effectiveness of end brackets is to include allowance for
the curvature of the hull.
- For primary support members subjected to lateral pressure, the
net section modulus requirement is to comply with the requirements in Pt 10, Ch 3, 3.11 Scantling requirements 3.11.3.
- For primary support members subjected to lateral pressure, the
net cross-sectional area of the web is to comply with the requirements in Pt 10, Ch 3, 3.11 Scantling requirements 3.11.3.
- Primary support members are generally to be analysed with the
specific methods as described for the particular structure type. More advanced
calculation methods may be required to ensure that nominal stress level, for
all primary support members are less than permissible stresses and stress
coefficients given in Pt 10, Ch 3, 3.11 Scantling requirements 3.11.3 and Pt 10, Ch 3, 3.11 Scantling requirements 3.11.3, when subjected to the applicable
design load sets.
|