Section
6 Hull construction
6.1 General
6.1.3 Materials for the hull structures subjected to low temperature are to
comply with Pt 3, Ch 2, 2.2 Refrigerated spaces relating to refrigerated spaces and adjacent
structures, or with Chapter 6 of the Rules for Ships for Liquefied
Gases, as applicable.
6.1.4 Subdivision
and damage stability are not covered by these Rules. However, attention
must be given to any relevant statutory regulations of the National
Authority of the country in which the ship is to be registered or
in which the plant is to be operated.
6.2 Location of accommodation, service and control spaces
6.2.1 All
accommodation and other compartments not directly essential to the
operation of the plant are to be arranged well clear of plant spaces,
and feedstock and product tanks.
6.2.2 Service
and control stations essential to the operation of the plant must
be made `gas-safe' in accordance with internationally accepted codes
and standards, and should, wherever possible, be so located that access
thereto is from a defined safe space. If such location is not possible,
the station is to be specially ventilated.
6.3 Integrity of gastightness between compartments
6.3.1 Where
integrity of gastightness is required between compartments containing
the plant, this is to be maintained in way of pipe tunnels or duct
keels where these traverse such compartments.
6.4 Cofferdams
6.4.2 Cofferdams are to be arranged around independent tanks containing chemical
products or effluents where these are separate from the ship structure, but permanently
connected thereto. Such cofferdams are to be mechanically ventilated using portable or
permanent systems as required by Chapter 12 of
the Rules for Ships for Liquid Chemicals, and are to be of sufficient size to allow
effective inspection of all the tank and ship structure in way.
6.5 Access and openings to spaces
6.5.2 Arrangements
are to be made to provide easy access to, or escape from, plant working
spaces. In general, ladders are not to be arranged vertically, and
intermediate platforms are to be fitted at vertical intervals of about
6 m. Ladders and platforms are to have guard rails and permanent provision
made for attaching hoists for use in emergencies. The arrangements
for the emergency hoists are to allow a clear, unobstructed lift to
the outside deck.
6.6 Longitudinal strength
6.6.1 Longitudinal
strength calculations are to be made in accordance with Pt 3, Ch 4 Longitudinal Strength for the following conditions,
and the Loading Manual required by Pt 3, Ch 4, 8 Loading guidance information is to include this information:
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Sea-going
conditions:
These conditions are to take account of the weights and disposition
of all ballast, plant items including any working fluids, other substances,
spare gear, etc. and any special support bracing where thermal effects
are considered, which will be on board during any sea-going condition
of the plant appropriate to the category of ship.
-
Harbour
condition:
This condition is to take account of the weights and disposition
of all ballast and plant items, including all working and other substances
(in all intended stowage dispositions) and spare gear which will be
on board during operation of the plant in harbour.
6.7 Plant support structure
6.7.1 Decks
and other structure supporting the plant are, in general, to comply
with the requirements of Pt 3 Ship Structures (General). Such
structure can, however, be considered on the basis of an agreed uniformly
distributed loading in association with local loads at plant support
points, provided that adequate transverse strength of the ship is
maintained.
6.7.2 Where
the nature and dispositions of heavy plant items are such that forces
on the ship and support structure due to ship motions are significant
(whether underway with or without working fluids, or moored with working
fluids), calculations of the loading and the structural response are
to be submitted. In this respect, the guidance formulæ for accelerations
as given in the Rules and Regulations for the Construction and Classification of Ships for the Carriage of Liquefied Gases in Bulk, July 2022 can
be used where appropriate. Details of the mass distribution and support
points of the plant items are to be submitted in all cases.
6.7.3 Where
model tests or reliable direct calculation procedures are used to
estimate wave-induced responses and which may indicate accelerations
and motion amplitudes differing from those arising from the application
of the Rules, such values will be taken into account in the approval
of support structure.
6.7.4 If the
vessel is intended for limited service at sea (e.g. a `once only'
voyage from port of build to service location), a reduction in the
Rule accelerations and motion amplitudes may be permitted. In order
to apply such a reduction, details of the intended service limitation
should be submitted.
6.8 Loading due to wave-induced motions
6.8.1 In cases
where the mass distribution of large columnar plant items is such
that the centre of action of the dynamic force differs significantly
from the centre of gravity of the item, due account of this is to
be taken in the calculation of the forces and moments at the support
positions.
6.9 Additional loads
6.9.1 The
structure supporting the plant is also to be capable of withstanding
forces arising from the following:
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Wind loads (in
all conditions of service and all categories of ships).
-
The angle of static
heel arising from the emergency condition referred to in Pt 7, Ch 2, 3.1 General 3.1.3 or Pt 7, Ch 2, 3.1 General 3.1.4, as applicable.
-
For a Category
1 A ship, a collision force acting on the tank corresponding to one-half
of the weight of the item with or without working fluids, as appropriate,
to the approved sea-going conditions from forward and one-quarter
of the weight of the item from aft.
-
For all other
categories of ship, a collision force from any horizontal direction
of one-fifth of the weight of the item.
6.10 Allowable stresses in support structure
6.10.1 The
following stress levels are applicable in conjunction with the loading
on the support structure:
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Support members
above or below the weather deck which are not subject to main hull
girder loading:
direct stress:
σa + σb = 0,6σy
shear stress:
τ = 0,6τy or 0,35σy whichever
is the smaller
combined stress:
- where
|
= |
the algebraic sum of
the axial and bending stresses at the point under consideration |
|
σy
|
= |
specified
minimum tensile yield stress or 0,2 per cent proof stress at room
temperature |
|
τy
|
= |
shear
yield stress. |
-
Support members
directly connected to hull structure and subject to transference of
loading therefrom:
- the maximum allowable direct, shear and combined stresses as defined
in (a), but with member local loading increased by a factor of 1,30,
or
- when the stresses in such structure are determined using methods
which satisfactorily take into account any ship deflection and load
transference in way of supports, no load factor need be applied.
-
Primary members
forming an integral ship structural and plant support system:
- in general, the allowable stresses in such a system will be especially
considered on the basis of the degree of refinement employed in the
load prediction, structural response and stress analysis methods.
Structural response calculations should include the interaction effects
of the hull and plant item.
6.10.2 In
general, all seatings, platform decks, girders and pillars supporting
plant items are to be arranged to align with the main hull structure,
which is to be suitably reinforced, where necessary, to carry the
appropriate loads. Attention should be paid to the capability of the
support structure to withstand buckling.
6.11 Integrity of weather deck
6.11.1 The
integrity of the weather deck is to be maintained. Where items of
plant equipment penetrate the weather deck and are intended to constitute
the structural barrier to prevent the ingress of water to spaces below
the freeboard deck, their structural strength is to be equivalent
to the Rule requirements for this purpose. Otherwise such items are
to be enclosed in superstructures or deckhouses fully complying with
the Rules. Full details are to be submitted for approval.
6.12 Equipment
6.12.1 Anchors
and chain cables for ships navigating at sea are to comply with the
requirements of Pt 3, Ch 13, 7 Equipment.
Special consideration will be given to the equipment required for
ships of Categories 1B and 2.
6.13 Gangways and freeing arrangements
6.13.1 Gangways
are to be sufficient to provide proper access to all areas necessary
for ship safety while the ship is operational and while it is at sea,
and are to be to the Surveyor's satisfaction.
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