Section 4 Machinery space
Clasification Society 2024 - Version 9.40
Clasifications Register Rules and Regulations - Rules and Regulations for the Classification of Offshore Units, July 2022 - Part 10 Ship Units - Chapter 3 Scantling Requirements - Section 4 Machinery space

Section 4 Machinery space

Parent topic: Chapter 3 Scantling Requirements

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.
  1. 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.
  2. 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.
  3. 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.
  1. 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.
  2. 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.
  3. 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.
  4. 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.
  5. 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.
  6. 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.
  1. 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 Table 3.2.1 Minimum net thickness for plating and local support members in the cargo tank region and Table 3.2.2 Minimum net thickness for primary support members in cargo tank region, except as applicable in Table 3.4.1 Minimum net thickness of structure in the machinery space.

    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
  1. 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.
4.3.2  Bottom shell plating.
  1. The keel plate breadth is to comply with the requirements in Pt 10, Ch 3, 2.3 Hull envelope plating 2.3.1.(a).
  2. The thickness of the bottom shell plating (including keel plating) is to comply with the requirements in Pt 10, Ch 3, 4.9 Scantling requirements 4.9.1.(a).
4.3.3  Bottom shell stiffeners.
  1. The section modulus and thickness of bottom shell stiffeners are to comply with the requirements in Pt 10, Ch 3, 4.9 Scantling requirements 4.9.1.(b) and Pt 10, Ch 3, 4.9 Scantling requirements 4.9.1.(c).
4.3.4  Girders and floors.
  1. The double bottom is to be arranged with a centreline girder.
  2. 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.
  3. Where the bottom is transversely framed, plate floors are to be fitted at every frame.
  4. 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.
  5. 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.
  1. 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
  1. 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.
  1. The scantlings of the side shell plating and longitudinals are to be properly tapered from the midship region towards the aft end.
  2. A suitable scarphing arrangement of the longitudinal framing is to be arranged where the longitudinal framing terminates and is replaced by transverse framing.
  3. Stiffeners and primary support members are to be supported at their ends.
4.4.2  Side shell plating.
  1. The thickness of the side shell plating is to comply with the requirements in Pt 10, Ch 3, 4.9 Scantling requirements 4.9.1.(a). Where applicable, the thickness of the side shell plating is to comply with the requirements in Pt 10, Ch 3, 2.3 Hull envelope plating 2.3.4.(a).
4.4.3  Side shell local support members.
  1. 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.(b) and Pt 10, Ch 3, 4.9 Scantling requirements 4.9.1.(c).
  2. 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.
  1. Web frames are to be connected at the top and bottom to members of suitable stiffness, and supported by deck transverses.
  2. The spacing of web frames in way of transversely framed machinery spaces is generally not to exceed five transverse frame spaces.
  3. 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.
  4. 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.
  5. 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.
  1. 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.
  2. The corners of the machinery space openings are to be of suitable shape and design to minimise stress concentrations.
  3. 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.
  4. 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.
  5. 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.
  6. 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.
  7. The structural scantlings are not to be less than the requirement for tank boundaries if the deck forms the boundary of a tank.
  8. 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.
  1. The plate thickness of deck plating is to comply with the requirements in Pt 10, Ch 3, 4.9 Scantling requirements 4.9.1.(a).
  2. 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.(b) and Pt 10, Ch 3, 4.9 Scantling requirements 4.9.1.(c).
  3. The web depth of deck stiffeners is to be not less than 60 mm.
  4. 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.
  5. 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.
  6. 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.
  1. Pillars are to comply with the requirements of Pt 10, Ch 3, 3.5 Deck structure 3.5.4.
  2. 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.
  1. 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.
  2. 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.
  3. 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.
  1. 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.
  2. 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.
  1. 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.
  1. Tanks are to comply with the requirements of Pt 10, Ch 3, 3.6 Tank bulkheads, with scantlings determined using the factors from Table 3.4.2 Permissible bending stress coefficient for plating and Table 3.4.3 Permissible bending stress coefficient for stiffeners.

    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
    Mv-total = design vertical bending moment at longitudinal position under consideration for the design load set being considered, in kNm Mv-total is to be calculated in accordance with Table 2.6.1 Design load combinations in Pt 10, Ch 2 Loads and Load Combinations using the sagging or hogging still water bending moment
    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

4.8.1  General.
  1. Watertight boundaries are to comply with the requirements of Pt 10, Ch 3, 3.7 Watertight boundaries, with scantlings determined using the factors from Table 3.4.2 Permissible bending stress coefficient for plating and Table 3.4.3 Permissible bending stress coefficient for stiffeners.

4.9 Scantling requirements

4.9.1  Plating and local support members.
  1. For plating subjected to lateral pressure, the net plating thickness is to comply with the requirements of Table 3.2.3 Thickness requirements for plating, where Ca is taken as given in Table 3.4.2 Permissible bending stress coefficient for plating.
  2. For stiffeners subjected to lateral pressure, the net section modulus requirement is to comply with the requirements of Table 3.2.4 Section modulus requirements for stiffeners, where Cs is taken as defined in Table 3.4.3 Permissible bending stress coefficient for stiffeners.
  3. For stiffeners subjected to lateral pressure, the net web thickness based on shear area requirements is to comply with the requirements of Table 3.2.5 Web thickness requirements for stiffeners, 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.
  1. 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.
  2. 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.(b).
  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.(c).
  4. 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.(b) and Pt 10, Ch 3, 3.11 Scantling requirements 3.11.3.(c), when subjected to the applicable design load sets.
4.9.3  Corrugated bulkheads.
  1. Special consideration will be given to the approval of corrugated bulkheads, where fitted.

    NOTE

    Scantling requirements of corrugated bulkheads in the cargo tank region may be used as a basis, see Pt 10, Ch 3, 2.6 Bulkheads 2.6.6 and Pt 10, Ch 3, 2.6 Bulkheads 2.6.7.

4.9.4  Pillars.
  1. The maximum load on a pillar is to be less than the permissible pillar load as given by the requirements in Pt 10, Ch 3, 3.11 Scantling requirements 3.11.5.
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