Trials

If the Administration consider it necessary it should require full-scale trials to be undertaken in which loadings are determined. Cognizance should be taken of the results where these indicate that loading assumptions of structural calculations have been inadequate. (see note 2)

Note:

1. The vibration check shall be performed during the sea trials of the craft. Where deemed necessary, the Society may require vibration measurements to be carried out using suitable instruments; where appropriate, remedial measures may be required to adequately eliminate situations deemed unacceptable.

2. The loading assumptions of structural calculation may include the requirements specified in C3.4, C3.5 and C3.6 of these Rules. Where these loading assumptions are deemed inadequate, cognizance should be taken.

C3.1 Application

C3.1.1 The scantling required in this chapter apply to craft constructed of steel, aluminium alloy or fibre reinforced plastic.

C3.1.2 This chapter is applied to the type of monohull craft, catamaran, SES, ACV and hydrofoil craft etc.

C3.1.3 Where novel structure or material is designed, reasonable design method or equivalent standard may be specially considered.

C3.1.4 The definitions of the following symbols and terms are applicable for this chapter:

L = length of craft, same as Lbp(m) (Amidships=L/2) FP = forward perpendicular

AP = after perpendicular

B = maximum moulded breadth (m)

D = moulded depth (m),measured from moulded base line to moulded deckline at the uppermost continuous deck amidship

d = moulded draft of full loaded condition (m)

 = moulded displacement at d, in seawater (specific weight = 1.025) (tones) Cb = block coefficient

=/(1.025·L·Bw·d)

V = maximum service speed, in knots g = acceleration of gravity, 9.81 m/s²

LCG = longitudinal center of gravity of the craft (m).

Chine – for craft without clearly identified chine, the chine is the hull point at which the tangent to the hull is inclined 50° to the horizontal.

Bottom – the lower part of hull between the keel and the chine.

Side – the part of hull between the chine and the main deck.

Main deck – the uppermost complete deck of the hull.

Cross structure – the structure connecting two hulls.

Deadrise angle – for craft without clearly identified deadrise angle, the deadrise angle is to be taken from horizontal line to the line joining the baseline at center and the chine.

C3.2 Materials and Connections

C3.2.1 General requirements

.1 All materials, intended for the use in the construction or repair of high speed crafts which are classed or are proposed for classification to the Society, are to be manufactured, tested and inspected in accordance with the requirements in this section.

.2 Materials which comply with national or proprietary specifications may be accepted provided that these specifications give reasonable equivalence to the requirements of this section.

C3.2.2 Steel structures

The material provisions of steel, forgings, and castings are to comply with the requirements in Part XI of the Rules for the Construction and Classification of Steel Ships.

C3.2.3 Aluminum alloy structures

The material provisions of aluminum alloys are to the referred to comply with the requirements in Part XI of the Rules for the Construction and Classification of Steel Ships.

With regard to welding of aluminum alloys, it is recommended that reference should be made to the following standards:

.1 JIS Z3604 “Recommended Practice for Inert Gas Shielded Arc Welding of Aluminum Alloy”

.2 AWS Structural Welding Code-Aluminum.

C3.2.3.1 Aluminum alloys for hull structures, forgings and castings

.1 The designation of aluminum alloys used here complies with the numerical designation used in RRIAD (Registration Record of International Alloy Designation).

.2 The characteristics of aluminum alloys to be used in the construction of aluminum craft are to comply with the relevant requirements of the Society Rules.

.3 As a rule, series 5000 aluminum-magnesium alloys or series 6000 aluminum-magnesium-silicon alloys (in Part XI of the Rules for the Construction and Classification of Steel Ships) shall be used.

.4 The use of series 6000 alloys or extruded platings, for parts which are exposed to sea water atmosphere, will be considered in each separate case by the Society, also taking into account the protective coating applied.

.5 The list of aluminum alloys given in tables mentioned in paragraph C3.2.3.1.3 is not exhaustive. Other aluminum alloys may be considered, provided the specification (manufacture, chemical composition, temper, mechanical properties, welding, etc.) and the scope of application be submitted to the Society for review.

.6 In the case of welded structures, alloys and welding processes are to be compatible and appropriate to the satisfaction of the Society and in compliance with the relevant Rules.

.7 For forgings or castings, requirements for chemical composition and mechanical properties are to be defined

in each separate case by the Society.

.8 In the case of structures subjected to low service temperatures or intended for other particular applications, the alloys to be employed are to be defined in each separate case by the Society. The acceptability requirements and conditions are to be stated.

.9 Unless otherwise specified, the Young’s modulus for aluminum alloys is equal to 70000 N/mm² and the Poisson’s ratio equal to 0.33.

C3.2.3.2 Influence of welding on mechanical characteristics

.1 Welding heat input lowers locally the mechanical strength of aluminum alloys hardened by work hardening (series 5000 other than condition 0 or H111) or by heat treatment (series 6000).

.2 Consequently, a drop in mechanical characteristics of welded structures is necessary to be considered in the heat-affected zone, with respect to the mechanical characteristics of the parent material.

.3 Aluminum alloys of series 5000 in 0 condition (annealed) or in H111 condition (annealed flattened) are not subject to a drop in mechanical strength in the welded areas.

.4 Aluminum alloys of series 5000 other than condition 0 or H111 are subjected to a drop in mechanical strength in the welded areas. The mechanical characteristics to consider are, normally, those of condition 0 or H111.

Higher mechanical characteristics may be taken into account, provided they are duly justified.

.5 Aluminum alloys of series 6000 are subject to a drop in mechanical strength in the vicinity of the welded areas. The mechanical characteristics to be considered are, normally, to be indicated by the supplier.

C3.2.3.3 Painting against corrosion

.1 Structural members of aluminum alloys works are recommended to be coated with a suitable paint.

.2 Any direct contact between steel and aluminum alloy is to be avoided (e.g. by means of zinc or cadmium plating of the steel parts and application of a suitable coating on the corresponding light alloy parts).

.3 The use of transition joints made of aluminum/steel-cladded plates or profiles is subject to the Society’s agreement.

C3.2.4 Welded connections

All the requirements concerning about the welding are to comply with the requirements in Part XII of Rules for the Construction and Classification of Steel ships.

C3.2.5 Fiber reinforced plastic (FRP) structures

The material provisions of fiber reinforced plastic construction are comply with the requirements in Part I of the Rules and Regulations for the Construction and Classification of Ships of Fibreglass Reinforced Plastic.

C3.3 Design vertical acceleration

V = craft speed,(knots)

BW = maximum waterline breadth (m), breadth of one hull for muti-hull craft LW = waterline length, at draft d (m)

acg = average 1/100 highest accelerations of the craft at LCG, expressed in g, (where g = 9.81m/s²).

C3.3.3 The relationships between allowable speed and significant wave height shall be stated in the “Craft Operation Manuals” and be shown on navigation bridge by signal board.

C3.3.4 The designer is to assume a wave height which may be encountered according to the craft’s service restriction as shown in Table C3.3.1.

Table C3.3.1

Area of operation Significant wave

height Fs

Unrestricted service area H1/3 4.0m 1.0 Restricted service area H1/3 4.0m 0.7 H1/3 2.0m 0.5 Smooth sea service area H1/3 0.5m 0.3 Fs = factor of service restriction

H1/3 = significant wave height

C3.3.5 The design vertical acceleration at longitudinal position other than LCG is to be in accordance with follows:

ax = kv．acg

where

acg=vertical acceleration at LCG, as specified in C3.3.2

kv=longitudinal distribution factor of vertical acceleration given in Figure C3.3.1

Figure C3.3.1 Acceleration Distribution kv

C3.4 Design pressure

C3.4.1 The design slamming pressure at LCG on bottom of craft is to be taken as:

Pcg = LwB

100Δ(1 + acg) KakN/m²

where:

acg = vertical acceleration at LCG,(g) Ka = design factor for impact area

0 0.1 0.2 0.3 0.4 0.5 0.6 0.7 0.8 0.9 1.0 FP 2.0

1.0 0.8

AP kv

= 0.62 – 0.47 transverses, stiffeners and girders, it is the shell area supported by them, but need not be taken less than 0.33l², where S is spacing of longitudinals or stiffeners (cm) and l is length of unsupported span of internals, see

C3.4.2 The design slamming pressure at longitudinal position other than LCG is to be as follows:

Px = Pcg·



ax = vertical acceleration at any longitudinal position (g), as specified in C3.3.5 Pcg = slamming pressure at LCG as specified in C3.4.1

C3.4.3 The pressure acting on weather deck is to be calculated as follows:

Pd = 0.2L + 7.6 kN/m²

C3.4.4 The pressure acting on unexposed deck is to be calculated as follows:

Pd = 0.1L + 6.1 kN/m²

C3.4.5 The pressure acting on enclosed accommodation decks is to be as follows:

Pd = 5.0 kN/m²

C3.4.6 Where the deck is designed to carry deck cargo, the pressure acting on the deck is to be calculated.

Pd = W (1 + 0.5ax) kN/m² where:

W= deck cargo load (kN)

ax= vertical acceleration of the craft at the longitudinal position considered (g)

C3.4.7 The pressure acting on the front wall of superstructure and deck house is to be as follows:

Ph = 24.0 kN/m² to plating and stiffeners

C3.4.8 The pressure acting on the side and aft end wall of superstructure and deck house is to be as follows:

Ph = 13.0 kN/m² to plating Ph = 10.0 kN/m² to stiffeners

C3.4.9 The pressure acting on the house top, to plating and to stiffeners are to be as follows:

Ph = 7.0 kN/m²

C3.4.10 The pressure acting on collision bulkhead and watertight bulkhead is to be calculated as follows:

Ph = 10h kN/m² where:

h = height from considered point up to bulkhead deck at center (m).

C3.4.11 The pressure acting on tank boundaries is to be calculated as follows:

Ph = 10h kN/m² where:

h = The greatest height from the considered point to the greatest of following:

(1) 2/3 air pipe height from tank top.

(2) 2/3 distance to weather deck.

(3) 0.01L + 0.15 (m) (4) 0.46m

C3.4.12 The slamming pressure acting on cross structures is to be calculated as follows:

P = K1K2VVR

(1-1/3 A

H

G ) kN/m²

where:

GA = air gap, height of the underside of cross deck above lightest draft waterline (m) K1 = longitudinal distribution factor as shown in Figure C3.4.1

Figure C3.4.1 K1

K2 = cross deck impact factor

= 0.17 for protected structure

= 0.33 for unprotected structure V = ship’s speed (knots)

VR =

W 1/3

L H 8

+ 2, (knots)

H1/3 = as defined in C3.3.2

C3.4.13 Sea pressure acting on bottom shell is to be calculated as follows:

Ph= 10(FsH + d) kN/m² where:

Fs = factor of service restriction as shown on Table C3.3.1 H = wave parameter

= 0.0172L + 3.653 (m) d = moulded draft (m)

C3.4.14 Sea pressure acting on side shell is to be calculated as follows:

FP 2.0

1.0

AP 0.75

Ph = 10(FsH + h) kN/m² where:

Fs,H = as specified in C3.4.13

h = height from the load point to the design waterline for load point below the design waterline, and 0 for load point on or above the design waterline (m).

C3.5 Hull girder strength

C3.5.1 For ships having L > 50 m or with L/D > 12, the longitudinal strength of hull girder in high speed navigation condition, specified in C3.5.4, and in displacement condition, specified in C3.5.5, are to be checked.

C3.5.2 For twin-hull craft and SES, the transverse strength, specified in C3.5.7, and torsional strength of cross-deck, specified in C3.5.8, are also to be checked.

C3.5.3 For hydrofoil craft, the calculation of longitudinal strength is to be effected for the most severe condition from hull-borne, take-off mode to foil-borne.

C3.5.4 The longitudinal bending moments in high speed navigation condition are to be assumed as follow:

MBH = MBS = 0.55L(Cb+0.7)(1+acg) kN-m where:

MBH = longitudinal hogging bending moment MBS = longitudinal sagging bending moment

C3.5.5 The longitudinal bending moments in displacement condition are to be assumed as follows:

MBH = MSW + 0.19CWL²BCb kN-m MBS = MSW + 0.11CWL²B(Cb + 0.7) kN-m where:

L, B, Cb are as defined in C3.1.4.

MSW = still water bending moment in most severe loading condition (kN-m) CW= 6 + 0.02L

C3.5.6 The shear force is to be assumed as follows:

TB = L 4MB

kN where:

MB = The greater of MBH and MBS as specified in C3.5.4 and C3.5.5 as applicable L = as defined in C3.1.4

C3.5.7 The transverse bending moment for twin-hull craft of L＜50m is to be assumed as follows:

MB = g

5 a b _cg

 

 kN-m

where:

b = transverse distance, in m, between the center line of two hulls.

g,  = as defined in C3.1.4 acg = as defined in C3.3.2

C3.5.8 The transverse bending moment for twin-hull craft of L ≥ 50 m is to be assumed as the greater of follows:

MB = MS (1 + acg) kN-m

MB = MS + Fy (z – 0.75T) kN-m where:

MS = still water transverse bending moment (kN-m) Fy = horizontal split force on immersed hull

= 

Z = height from base line to neutral axis of cross structure (m)

L

V needs not be taken greater than 3

d = full load draft (m).

C3.5.9 The vertical shear force in centerline between twin-hull is to be assumed as follows:

g

4

T a^cg

B    kN

C3.5.10 The twin-hull pitch connection moment may be assumed as follows:

Mp= g

8 a L cg 

 kN-m

C3.5.11 The twin-hull torsional moment, along the longitudinal axis is to be assumed as follows:

Mt = g

b = transverse distance between the center line of the two hulls (m).

C3.5.12 The required section modulus, respectively at bottom and main deck are to be calculated as follows:

SM = Q

17.5M  ×102 cm³ where:

M = longitudinal bending moment assumed in C3.5.4 or C3.5.5 Q = material factor

y = minimum yield stress of unwelded parent material (N/mm²).

u = minimum ultimate strength of welded aluminium (N/mm²).

for FRP:

Q = 320/u

where:

u = minimum ultimate tensile or compressive strength whichever is less (N/mm²).

C3.6 Direct Calculations

C3.6.1 General

.1 Direct calculations generally require to be carried out, in the opinion of the Society, to check primary structures for craft of length L > 90 m or speed V > 45 knots.

.2 In addition, direct calculations are to be carried out to check scantlings of primary structures of craft whenever, in the opinion of the Society, hull shapes and structural dimensions are such that scantling formulas in C3.7 and C3.8 are no longer deemed to be effective.

C3.6.2 Loads C3.6.2.1 General

.1 In general, the loading conditions specified in C3.6.2.2 are to be considered .2 The slamming pressure is to be calculated as stipulated in C3.4.

.3 In three-dimensional analyses, special attention is to be paid to the distribution of weights and buoyancy and to the dynamic equilibrium of the craft.

In the case of three-dimensional analysis, the longitudinal distribution of impact pressure is to be considered individually, in the opinion of the Society. In general, the impact pressure is to be considered as acting separately on each transverse section of the model, the remaining sections being subject to the hydrostatic pressure.

C3.6.2.2 Loading conditions .1 Still-water condition:

The following loads are to be considered:

– forces caused by weights which are expected to be carried in the full load condition. The weight is distributed according to the weight booklet of the craft.

– outer hydrostatic load in still water.

.2 Vertical acceleration condition:

The following loads are to be considered:

– forces caused by weights which are expected to be carried in the full load condition. The weight is distributed according to the weight booklet of the craft.

– forces of inertia due to the vertical acceleration ax of the craft, considered in a downward direction.

.3 Slamming pressure condition:

The slamming pressure on the bottom and the side shell of the craft is to be considered.

.4 Horizontal split force condition for catamaran:

The horizontal split force on immersed hull of catamaran is to be considered.

.5 Pitch connecting moment condition for catamaran:

The pitch connecting moment on the cross deck of a catamaran is to be considered.

C3.6.3 Structural model

.1 In general, the extent of the model is to be such as to allow analysis of the behaviour of the main structural elements and their mutual effects.

.2 In general, primary structures of crafts are to be modeled with finite element adopting a medium size mesh. In the opinion of the Society, detailed analysis with finite mesh are required for areas where stresses, calculated with medium-mesh, exceed allowable limits and the type of structure gives reason to suspect the presence of high stress concentrations.

C3.6.4 Boundary conditions

The boundary conditions depend on the model extent and the loading conditions considered.

Km = coefficient depending on the material:

= 1.00 for steel structures

= 2.15 for aluminum alloy structures Ks = safety coefficient, to be assumed:

= 1.00 for combined loading conditions

= 1.25 for loading condition in still water.

.2 For non-metal structures, allowable stresses are to be defined according to criteria specified by the Society.

C3.7 Steel and Aluminum Alloy Craft

C3.7.1 General

This Article stipulates requirements for the scantlings of hull structures (plating, stiffeners, primary supporting members). The loads acting on such structures are to be calculated in accordance with the provisions of C3.4.

C3.7.2 Plating

The thickness of the shell, deck or bulkhead plating is not to be less than obtained from C3.7.2.1 to C3.7.2.3, whichever is greater:

C3.7.2.1 Thickness due to lateral loads

σa

k1 = correction factor for curved panels, given in Table C3.7.1

= as shown in Figure C3.7.1 (mm)

= design pressure given in C3.4 (kN/m²)

k2 = 1 0.623(s)6

0.5

 l

a = allowable stress given in Table C3.7.2 (N/mm²) l = longer edge of plate panel (mm).

Table C3.7.1

h/s k1

0 ~ 0.03 1.0

0.03 ~ 0.1 1.1 - 3 ∙ h/s

≥ 0.1 0.8

Figure C3.7.1 Measurement of Curvature

Table C3.7.2

Structural Members Allowable stress, a

Bottom and side shell plating –slamming pressure 0.90y

Bottom and side shell plating – sea pressure 0.55y

Deck plating – strength deck 0.60 y

Deck plating – lower deck 0.60 y

Bulkheads – tank boundary 0.60 y

Bulkheads – watertight 0.95y

Superstructures and deckhouses– front, sides, ends, tops 0.60 y

Note :y = yielding strength of steel or aluminum (N/mm²).

C3.7.2.2 Buckling strength

These requirements apply to plate panels subject to compressive load.

.1 Elastic buckling stress

E )2

st ( E m

σ 0.9 N/mm²

where:

E = elastic buckling stress (N/mm²)

=4.0 for longitudinally framed plate panel

=^C

[

^{1 (s)2}

]

²

 l , for transversely framed plate panel

= Young’s modulus (N/mm²)

s

h

= 2.06 x 10⁵ N/mm², for steel

= 6.90 x 10⁴ N/mm², for aluminum

= plate thickness (mm)

= shorter edge of plate panel (mm) l = longer edge of plate panel (mm)

= 1.21 where stiffeners are T or angle sections

= 1.10 where stiffeners are bulb plates

E elastic buckling stress calculated in C3.7.2.2.1 (N/mm²)

y yielding strength of material (N/mm²).

M total bending moment given in C3.5(KN-m)

y vertical distance from the neutral axis to the considered location (m) I moment of inertia of the hull girder (cm⁴).

.4 Buckling strength criteria

c W

C3.7.2.3 Minimum thickness

The thickness of shell, decks, and bulkheads is not to be less than obtained from Table C3.7.3:

Table C3.7.3

Structural members Steel craft Aluminum craft

Bottom shell 0.44 Lq_s +2.0 Lower decks, W.T. bulkheads, deep tank bulkheads 0.35 Lq_s +1.0

(minimum 3.0 mm)

0.52 Lq_a +1.0 (minimum 3.5 mm) qs = 1.0 for ordinary strength steel; 245/σ for higher strength steels, but not to be taken less than _ys

0.72

qa = 115/σ for aluminum alloys _ya

σ = Yield strength for higher strength steel, in N/mmys ²

σ = Minimum unwelded yield strength for aluminum alloys, in N/mmya ² , but not to be taken as more than 0.7 of the ultimate tensile strength in the as-welded condition

C3.7.3 Stiffeners and primary supporting members

The scantling of each longitudinal, stiffener, transverse web, stringer and girder is not to be less than obtained from C3.7.3.1 to C3.7.3.3:

C3.7.3.1 Section modulus

The ends of members are to be effectively attached to the supporting structures. The section modulus of each longitudinal, stiffener, transverse web, stringer and girder is not to be less than given by the following equation:

3

s = spacing of longitudinal, stiffener, transverse web or girder (m)

l = span of longitudinal, stiffener, transverse in web or girder between supports, where bracket end connections are supported by bulkheads, l may be measured onto the bracket (m)

a = allowable stress given in Table C3.7.4 (N/mm²).

Table C3.7.4

Structural Members Allowable stress, a

Bottom longitudinals 0.50 y

Side longitudinals 0.50 y

Deck longitudinals – strength deck 0.33 y

Deck longitudinals – other deck 0.40 y

Bottom transverses 0.60 y

Side transverses 0.60 y

Deck transverses – strength decks 0.75 y

Deck transverses – other decks 0.75 y

Watertight bulkheads 0.85 y

Deep tank bulkheads 0.60 y

Superstructure and Deckhouse 0.70 y

Note :y = yielding strength of steel or aluminum (N/mm²).

C3.7.3.2 Buckling strength

These requirements apply to longitudinals, stiffeners, transverse webs, stringers and girders subject to compressive load.

.1 Elastic buckling stress

E = elastic buckling stress (N/mm²)

= Young’s modulus (N/mm²)

= 2.06 x 10⁵ N/mm², for steel

= 6.90 x 10⁴ N/mm², for aluminum

Ia = moment of inertia of the member being considered together with attached plating (cm⁴)

= cross-sectional area of the member being considered together with attached plating (cm²) l = span of longitudinal (m).

.2 Critical buckling stress

c = E, when E ≤ 0.5y

= )

σ 4 (1 σ σ

E

y  y , when E＞0.5y

where:

E elastic buckling stress calculated in C3.7.3.2 (N/mm²)

y yielding stress (N/mm²).

.3 Calculated compressive stress

W 105

I

σ M y _N/mm²

where:

W = working compressive stress in panel being considered (N/mm²)

W = working compressive stress in panel being considered (N/mm²)

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