C3.1 General
C3.1.1 Introductory comments
.1 This Section contains the requirements for
structural scantlings of the craft to which these Rules
apply, i.e. to craft for which V ≥ 7,16 Δ1/6. Craft for
which V/ L ≥ 10 shall be individually considered by
GL (V in knots, Δ in tonnes, L in metre).
For what concerns multihull craft, this Section provides the requirements for scantlings of catamarans
and trimarans. Other craft will be considered in each
separate case by GL.
.2 The requirements for scantlings of hydrofoils and air-cushion vehicles are contained in Appendices C3A1 and C3A2. Unless otherwise specified, the requirements of this Section apply to such
craft only as far as the provisions regarding limit
operating conditions, materials and construction
criteria are concerned.
.3 The scantlings indicated in the following
paragraphs apply to craft constructed of steel, aluminium alloy or fibre reinforced plastic, as specified in
C3.2.
C3.1.2 Direct calculations
C3.1.2.1 General
.1 GL may require direct calculations to be
carried out, if deemed necessary.
Such calculations are to be carried out based on structural modelling, loading and checking criteria described below. Calculations based on other criteria
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may be accepted if deemed equivalent to those laid
down by GL.
.2 In order to increase the flexibility in the
structural design of ships GL also accepts direct calculations with computer programs. The aim of such
analyses should be the proof of equivalence of a
design with the rule requirements.
.3 Direct calculations may also be used in order
to optimise a design; in this case only the final results
are to be submitted for review.
C3.1.2.2 General programs
.1 The choice of computer programs according
to "State of the Art" is free. The programs may be
checked by GL through comparative calculations
with predefined test examples. A generally valid
approval for a computer program is, however, not
given by GL.
.2 Direct calculations may be used in the following fields
– global strength
– longitudinal strength
– beams and grillages
– detailed strength
.3 For such calculation the computer model,
the boundary condition and load cases are to be
agreed upon with GL. The calculation documents are
to be submitted including input and output. During
the examination it may prove necessary that GL perform independent comparative calculations.
.4 GL is prepared to carry out the following
calculations of this kind within the marine advisory
services:
.4.1 Strength
Linear and/or non-linear strength calculations with
the FE-method:
For an automated performance of these calculations,
a number of effective pre- and post processing programmes is at disposal:
– calculation of seaway loads as per modified strip
method or by 3 D-panel method
– calculation of resultant accelerations to ensure
quasi-static equilibrium
– calculation of composite structures
– evaluation of deformations, stresses, buckling
behaviour, ultimate strength and local stresses,
assessment of fatigue strength
.4.2 Vibrations
Calculation of free vibrations with the FE-method as
well as forced vibrations due to harmonic or shock
excitation:
– global vibrations of hull, aft ship, deckhouse, etc.
– vibrations of major local components, such as
rudders, radar masts, etc.
– local vibrations of plate fields, stiffeners and
panels
– vibrations of simply or double-elastically mounted aggregates
A number of pre- and post processing programs is
available here as well for effective analyses:
– calculation of engine excitation forces/moments
– calculation of propeller excitation forces (pressure fluctuations and shaft bearing reactions)
– calculation of hydrodynamic masses
– graphic evaluation of amplitude level as per
ISO 6954 recommendations or as per any other
standard
– noise predictions
C3.1.2.3 Specific programs related to Rules
GLRP (GL RULES and Programs) is available on
CD-ROM. It includes the wording of GL-Rules and
an elementary program for dimensioning the structural members of the hull.
C3.1.3 Units
.1 Unless otherwise specified, the following
units are used in the Rules:
− thickness of plating [mm]
− section modulus of stiffeners [cm3]
− shear area of stiffeners [cm2]
− span and spacing of stiffeners [m]
− stresses [MPa]
− concentrated loads [kN]
− distributed loads [kN/m] or [kPa]
C3.1.4 Documents for Approval
The following documents are to be submitted. To
facilitate a smooth and efficient approval process
they shall be submitted electronically via GLOBE 1.
In specific cases and following prior agreement with
GL they can also be submitted in paper form in triplicate.
.1 Midship section
The cross sectional plans (midship section, other
typical sections) shall contain all necessary data on
the scantlings of the longitudinal and transverse hull
structure as well as details of anchor and mooring
equipment.
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1 Detailed information about the secured GL system GLOBE
can be found on GL’s website
www.gl-group.com/globe.
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.2 Longitudinal section
The plan of longitudinal sections shall contain all
necessary details on the scantlings of the longitudinal
hull structure and on the location of the watertight
bulkheads and the deck supporting structures, the
arrangement of superstructures and deck houses.
.3 Decks
Plans of the decks showing the scantlings of the deck
structures, length and breadth of cargo hatches, openings above the engine and boiler room, and other
deck openings. On each deck, deck load caused by
cargo is to be defined as assumed in determining the
scantlings of the decks and their supports.
.4 Shell
Drawings of shell expansion, containing full details
on the location and size of the openings and drawings
of the sea chests.
.5 Bulkheads
Drawings of the transverse, longitudinal and wash
bulkheads and of all tank boundaries, with details on
densities of liquids, heights of overflow pipes and set
pressures of the pressure or vacuum relief valves (if
any).
.6 Bottom structure
Drawings of single and double bottom showing the
arrangement of the transverse and longitudinal girders as well as the water and oil tight subdivision of
the double bottom.
.7 Engine and boiler seatings
Drawings of the engine and boiler seatings, the bottom structure under the seatings and of the transverse
structures in the engine room, with details on fastening of the engine foundation plate to the seating, as
well as type and output of engine.
.8 Appendages
Drawings of rudder, shaft brackets, stabilizers including supports, bearing materials and propeller details.
.9 Longitudinal strength
Maximum and minimum still water bending moments, shear forces and, if necessary, torsional moments. This includes the mass distribution for the
envisaged loading conditions and the distribution of
section moduli and moduli of inertia over the ship's
length.
.10 Materials
The drawings mentioned in 1 – 8 and 13 shall contain
details on the hull materials (e.g. hull structural steel
grades, standards, material numbers). Where higher
tensile steels or materials other than ordinary hull
structural steels are used, drawings for possible repairs have to be placed on board.
.11 Weld joints
The drawings listed in 1 – 8 and 13 shall contain
details on the welded joints e.g. weld shapes and
dimensions and weld quality. For the relevant data
for manufacturing and testing of welded joints see
Rules for Welding.
.12 Lashing and stowage devices
Drawings containing details on stowage and lashing
of cargo (e.g. containers, car decks). In the drawings
the location of the connections and the appropriate
substructures at the ship shall be shown in detail.
.13 Substructures
Drawings of substructures below steering gears,
windlasses and chain stoppers as well as masts and
boat davits, supporting structure of cargo masts,
cranes, etc. together with details on loads to be transmitted into structural elements.
.14 Additional information for fibre reinforced plastic (FRP) craft
For FRP craft, the drawing and documents to be
submitted for examination and listed in C3.1.4 are to
contain the following additional information:
− arrangement of laminate for the various structural
elements: thickness, definition of successive layers of reinforcement, areal weight of reinforcement layers, mass or volume fraction of reinforcement layers, directions of roving layers and
unidirectional reinforcements, decreasing in
thickness between layers
− direction of laminate in relation to craft structure
− structure of oil tanks or other liquid tanks which
are integrated into the hull
− details of connection among various structural
elements and details of attachment to the hull of
supplementary reinforcing elements
− pillars
Suppliers’ technical specifications with indication of
types, trademarks and references of resins and gelcoats, reinforcements and core materials are to be
supplied.
These specifications are to give the following information:
− resins: type (orthophthalic or isophthalic), specific gravity, Young’s modulus, Poisson’s ratio,
breaking strength and elongation at break
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− reinforcements (mats, woven rovings, unidirectional reinforcements): quality (glass or other material, with specific gravity, breaking strength of
the elementary fibre, Young’s modulus and Poisson’s ratio), mass per square metre, thickness and
possibly weft-warp distribution
− core materials: type and quality; specific gravity;
tensile, compressive and shear strength and elasticity moduli
C3.1.5 Definitions and symbols
The definitions of the following terms and symbols
are applicable throughout this Section and its Appendices and are not, as a rule, repeated in the different
paragraphs. Definitions applicable only to certain
paragraphs are specified therein.
− “Moulded base line”: The line parallel to the
summer load waterline, crossing the upper side of
keel plate or the top of skeg at the middle of
length L.
− “Hull”: The hull is the outer boundary of the
enclosed spaces of the craft, except for the deckhouses, as defined below.
− “Chine”: For hulls that do not have a clearly identified chine, the chine is the hull point at which
the tangent to the hull is inclined 50° to the horizontal.
− “Bottom”: The bottom is the part of the hull between the keel and the chines.
− “Main deck”: The main deck is the uppermost
complete deck of the hull. It may be stepped.
− “Side”: The side is the part of the hull between
the chine and the main deck.
− “Deckhouse”: The deckhouse is a decked structure located above the main deck, with lateral
walls inboard of the side of more than 4 per cent
of the local breadth. Structure located on the main
deck and whose walls are not in the same longitudinal plane as the under side shell may be regarded as a deckhouse.
− “Wet deck”: For multihull craft, the wet deck is
the bottom structure connecting the hulls which is
defined as cross-deck.
− “Deadrise angle αd”: For hulls that do not have a
clearly identified deadrise angle, αd is the angle
between the horizontal and a straight line joining
the keel and the chine. For catamarans with nonsymmetrical hulls (where inner and outer deadrise
angles are different), αd is the lesser angle.
− “Fore end”: Hull region forward of 0,9 L from the
aft perpendicular.
− “Aft end”: Hull region abaft of 0,1 L from the aft
perpendicular.
− “Midship area”: Hull region between 0,3 L and
0,7 L from the aft perpendicular.
L = Rule length [m], equal to LWL which is the
waterline measured with the craft at rest in
calm water and, for SESs, in the off-cushion
condition, for trimarans L will be defined in
each separate case at the discretion of GL.
FP = forward perpendicular, i.e. the perpendicular
at the intersection of the waterline at draught
T and the foreside of the stem
AP = aft perpendicular, i.e. the perpendicular located at a distance L abaft of the forward perpendicular
B = the greatest moulded breadth [m], of the craft
Bw = the greatest moulded breadth [m], measured
on the waterline at draught T; for catamarans,
Bw is the breadth of each hull; for trimarans,
Bw will be defined in each separate case at the
discretion of GL.
D = depth [m], measured vertically in the transverse section at the middle of length L from
the moulded base line of the hull(s) to the top
of the deck beam at one side of the main deck
(if the main deck is stepped, D will be defined
in each separate case at the discretion of GL)
T = draught of the craft [m], measured vertically
on the transverse section at the middle of
length L, from the moulded base line of the
hull(s) to the full load waterline, with the craft
at rest in calm water and, for SESs, in the offcushion condition
Δ = moulded displacement at draught T, in sea
water (mass density = 1,025 t/m3) [t]
CB = total block coefficient, defined as follows:
B
W
C
1,025 L B T
Δ = ⋅ ⋅ ⋅
For catamarans, CB is to be calculated for a single
hull, assuming Δ equal to one half of the craft’s displacement; for trimarans the calculation of CB depends on the distribution of displacement of each
hull. It will be defined in each separate case at the
discretion of GL.
V = maximum service speed [kn]
g = acceleration of gravity, equal to 9,81 m/s2
LCG = longitudinal centre of gravity of the craft.
C3.1.6 Rounding-Off Tolerances
Where in determining plate thicknesses in accordance
with the provisions of this Section the figures differ
from full or half mm, they may be rounded off to full
or half millimeters up to 0,2 or 0,7; above 0,2 or 0,7
mm they are to be rounded up.
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If plate thicknesses are not rounded the calculated
required thicknesses shall be shown in the drawings.
The section moduli of profiles usual in the trade and
including the effective width according to C3.7.4
may be 3 % less than the required values according to
the following rules for dimensioning.
C.3.1.7 Workmanship
C3.1.7.1 General
.1 Requirements to be complied with by the
manufacturer
.1.1 The manufacturing plant shall be provided
with suitable equipment and facilities to enable
proper handling of the materials, manufacturing
processes, structural components, etc. GL reserve the
right to inspect the plant accordingly or to restrict the
scope of manufacture to the potential available at the
plant.
.1.2 The manufacturing plant shall have at its
disposal sufficiently qualified personnel. GL is to be
advised of the names and areas of responsibility of all
supervisory and control personnel. GL reserve the
right to require proof of qualification.
.2 Quality control
.2.1 As far as required and expedient, the manufacturer's personnel has to examine all structural
components both during manufacture and on completion, to ensure that they are complete, that the dimensions are correct and that workmanship is satisfactory
and meets the standard of good shipbuilding practice.
.2.2 Upon inspection and corrections by the
manufacturing plant, the structural components are to
be shown to the GL Surveyor for inspection, in suitable sections, normally in unpainted condition and
enabling proper access for inspection.
.2.3 The Surveyor may reject components that
have not been adequately checked by the plant and
may demand their re-submission upon successful
completion of such checks and corrections by the
plant.
C3.1.7.2 Structural details
.1 Details in manufacturing documents
.1.1 All significant details concerning quality and
functional ability of the component concerned shall
be entered in the manufacturing documents (workshop drawings, etc.). This includes not only scantlings but - where relevant - such items as surface
conditions (e.g. finishing of flame cut edges and weld
seams), and special methods of manufacture involved
as well as inspection and acceptance requirements
and where relevant permissible tolerances. So far as
for this aim a standard shall be used (works or national standard, etc.) it shall be harmonized with GL.
This standard shall be based on the IACS Recommendation 47 Shipbuilding and Repair Quality Standard for New Construction. For weld joint details, see
Section C.3.2.4.1
.1.2 If, due to missing or insufficient details in
the manufacturing documents, the quality or functional ability of the component cannot be guaranteed
or is doubtful, GL may require appropriate improvements. This includes the provision of supplementary
or additional parts (for example reinforcements) even
if these were not required at the time of plan approval
or if - as a result of insufficient detailing - such requirement was not obvious.
.2 Cut-outs, plate edges
.2.1 The free edges (cut surfaces) of cut-outs,
hatch corners, etc. are to be properly prepared and are
to be free from notches. As a general rule, cutting
drag lines, etc. shall not be welded out, but are to be
smoothly ground. All edges should be broken or in
cases of highly stressed parts, should be rounded off.
.2.2 Free edges of flame or machine cut plates or
flanges are not to be sharp cornered and are to be
finished off as laid down in 2.2.1. This also applies to
cutting drag lines, etc., in particular to the upper edge
of shear strake and analogously to weld joints,
changes in sectional areas or similar discontinuities.
.3 Cold forming
.3.1 For cold forming (bending, flanging, beading) of plates the minimum average bending radius
shall not fall short of 3 t (t = plate thickness) and
shall be at least 2 t. Regarding the welding of cold
formed areas, see C3.6.1.2.6.
.3.2 In order to prevent cracking, flame cutting
flash or sheering burrs shall be removed before cold
forming. After cold forming all structural components and, in particular, the ends of bends (plate
edges) are to be examined for cracks. Except in cases
where edge cracks are negligible, all cracked components are to be rejected. Repair welding is not permissible.
.4 Assembly, alignment
.4.1 The use of excessive force is to be avoided
during the assembly of individual structural components or during the erection of sections. As far as
possible major distortions of individual structural
components should be corrected before further assembly.
.4.2 Girders, beams, stiffeners, frames, etc. that
are interrupted by bulkheads, decks, etc. shall be
accurately aligned. In the case of critical components,
control drillings are to be made where necessary,
which are then to be welded up again on completion.
.4.3 After completion of welding, straightening
and aligning shall be carried out in such a manner
that the material properties will not be influenced
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significantly. In case of doubt, GL may require a
procedure test or a working test to be carried out.
C3.1.8 Protection against corrosion
.1 Scantlings stipulated in C3.7 assume that the
materials used are chosen and protected in such a
way that the strength lost by corrosion is negligible.
.2 The Shipyard is to give GL a document
specifying all the arrangements made to protect the
material against corrosion at the construction stage:
coating types, number and thickness of layers, surface preparation, application conditions, control after
completion, anodic protection, etc. The GL Guidelines for Corrosion Protection and Coating Systems
(VI-10-2) are to be observed.
.3 This document shall also include maintenance arrangements to be made in service to restore
and maintain the efficiency of this protection, whatever the reasons of its weakening, whether incidental
or not.
.4 All such maintenance operations are to be
listed in a book shown to GL surveyor at each visit
