Section 1 General

101. Application

1. The rules in this chapter apply to ships to be registered in accordance with the Regulations for the Classification and Registry of Ships, less than 60 m in length, of fibre reinforced plastics (FRP) single skin and sandwich constructions for assignment of the main structures. Upon special consid- eration other fiber reinforced plastics than FRP may be accepted. The ships of 60 m or more in length shall be determined at the discretion of this Society.

2. The scantlings for hull structure's members of ship 60 m or more in length are in accordance with Guidance Relating to the Rules for Classification of High Speed and Light Crafts, Annex 3- 1, Guidance for the Direct Strength Assessment.

3. The requirements, not mentioned in this chapter, are to be in accordance with requirements in Ch

3 and 4.

102. Definitions

The definitions, except not defined in this chapter, are to be in accordance with following provisions.

(1) Fibreglass reinforcement

The fibreglass reinforcements are glass chopped strand mat (chopped mats), glass roving cloths (roving cloths) and glass roving (roving) of reinforcements for FRP manufactured from long fibres.

(2) Resins

The resins are liquid unsaturated polyester resins for laminating and gelcoat.

(3) Blending proportion

The blending proportion is a ratio in weight of the applied sclerotic and accelerator to the resin.

(4) Laminating

Laminating is an operation of laying succeeding glass fibre reinforcement impregnated with resin before curing or before the preceding layer advances in cure.

(5) Bonding

Bonding is an operation of connecting the FRP already advanced in cure with other FRP mem- bers, timbers, hard plastic foams, etc. by means of impregnating fibreglass reinforcements with resin.

(6) Moulding

Moulding is an operation of manufacturing FRP products with definite form, strength, etc. by means of laminating or bonding.

(7) Single skin construction

The single skin construction is a construction composed of FRP single panels moulded with fi- breglass reinforcement and resin.

(8) Sandwich construction

The sandwich construction is a construction having FRP layers adhered to the both sides of core materials such as hard plastic form, balsa, timber (including plywood), etc.

(9) Hand Lay-up Process

The hand lay-up process is a method of manual moulding by impregnating fibreglass reinforce- ments with resin.

103. Symbols

The symbols, used in Sec 4 to Sec 7, are to be in accordance with follows.

: laminate thickness (mm ).

sandwich core thickness (mm ).

: distance (mm ) between centerlines of opposite skin laminates of a sandwich panel.

tensile or compressive modulus of elasticity of FRP laminate (N mm ).

:

:

:

modulus of elasticity of core material given on type approval certificate (N mm ).

modulus of rigidity of sandwich core material given on type approval certificate.

: ultimate normal stress in tension or com pression of FRP laminate (N mm ).

: normal stress in FRP laminate (N mm ).

: combined bending and membrane stress (N mm

: ultimate shear stress of sandwich core material given on type approval certificate (N mm

: core shear stress in laterally loaded sandwich panel (N mm

: ).

: panel deflection (mm ).

: panel deflection factor.

: Poisson's ratio.

: design pressure (kN m ), defined in Ch 2.

: longest side of sandwich or single skin panel (m ).

104. Structural calculation

1. To determine stresses and deflections in FRP single skin and sandwich construction either direct calculations using the full stiffness and strength properties of the laminate in all directions or a simplified method in accordance with Sec 5 to 7 in this chapter will be accepted. However, direct calculation is to be in accordance with the discretion of the Society.

2. The simplified method may be employed on the following conditions.

(1) The principal directions of the laminate reinforcement is parallel to the panel edges.

(2) The difference in elastic modulus in the two principal directions is not more than 20 %.

(3) The skin laminates of sandwich panels are thin, i.e. is greater than 5.77.

105. Weight of fibreglass reinforcement and thickness of laminates

1. The thickness of laminates per ply of chopped mats or roving cloths may be as obtained from the following formula.

mm

: designed weight per unit area of chopped mats or roving cloths (g m ).

: glass content of laminate (ratio in weight) (%).

: specific gravity of cured resin.

: specific gravity of chopped mats or roving cloths.

2. The glass content ( ) specified in the preceeding Par 1 is preferable to be the value per ply for the actual laminates. However, it may be taken as the mean glass content of the whole laminates.

3. The specific gravity of chopped mats or roving cloths ( ) specified in the preceding Par 1

may be taken as 2.5 in calculation of the thickness, if nothing specially intervenes.

4. The specific gravity of cured resin ( ) specified in the preceding Par 1 may be taken as 1.2 in calculation of the thickness, unless any fillers are used in order to make the resin heavier.

5. Calculation of the thickness of laminates with fibreglass reinforcements other than chopped mats and roving cloths is to be in accordance with the discretion of the Society.

106. Bottom structures

1. Longitudinal stiffeners

(1) Single bottoms as well as double bottoms are normally to be longitudinally stiffened in yacht built in single skin construction. In yacht with sandwich construction the bottom panel stiffening will be considered in each individual case.

(2) The longitudinals should preferably by continuous through transverse members. At their ends longitudinals are to be fitted with brackets or to be tapered out beyond the point of support.

(3) Longitudinal stiffeners are to be supported by bulkheads and/or transverse.

2. Transverses

(1) Transverses are to be continuous around the cross section of yacht i.e. web and flange lami- nates of floors, side webs and deck beams are to be efficiently connected together. If inter- mediate floors are fitted their ends should be well tapered or connected to local panel stiffening.

(2) In the engine room, floors are to be fitted at every frame. The floors are preferably to be car-

ried continuously through the engine girders. In way of thrust bearings additional strengthening is to be provided.

3. Longitudinal girders

(1) Longitudinal girders are to be carried continuously through bulkheads. In yacht built in sandwich construction longitudinal girders are to be fitted to support the bottom panels.

(2) A center girder is to be fitted for docking purpose if the external keel or bottom shape does not give sufficient strength and stiffness.

(3) Openings should not be located at ends of girders without due consideration being taken to

shear loadings.

4. Engine girders

Main engines are to be supported by longitudinal girders with suitable local reinforcement to take the engine and gear mounting bolts. Rigid core materials to be applied in all through bolt connections.

5. Double bottom

Manholes are to be made in the inner bottom, floors and longitudinal girders to provide access to all parts of the double bottom. The vertical extension of openings is not to exceed one half of the girder height. Exposed edges of openings in sandwich constructions are to be sealed with resin im- pregnated mat. All openings are to have well rounded corners.

6. Bow impact protection

(1) yachts built in sandwich construction are to have the fore stem designed so that a local impact at or below the load line will not result in skin laminate peeling due to hydraulic pressure.

(2) To comply with the requirement in preceding (1) outer and inner skin laminate of the hull pan-

el shall be connected together as shown in Fig 3.5.1. The distance ( ) shall not less than fol- lowing formula. The vertical extension of the collision protection shall be from the keel to a

m

(3) The connection of the skin laminates shall be arranged in such a way that laminate peeling is effectively arrested (refer to, Fig 3.5.2).

(4) Other arrangements giving an equivalent safety against laminate peeling may be accepted based

on considerations in each individual case.

(5) Within the vertical extension of the collision protection the stem laminate shall be increased to a thickness not less than that obtained from the following formula :

mm

Fig 3.5.1 Collision protection Fig 3.5.2 Laminate connection

107. Deck structure

1. Decks of single skin construction are normally to be longitudinally stiffened.

2. The longitudinals should preferably be continuous through transverse members. At their ends longi- tudinals are to be fitted with brackets or to be tapered out beyond the point of support.

3. The laminate thickness of single skin constructions is to be such that the necessary transverse buck- ling strength is achieved, or transverse intermediate stiffeners may have to be fitted.

108. Bulwarks

1. Bulwark sides are to have the same scantlings as required for a superstructure in the same position.

2. A strong flange is to be made along the upper edge of the bulwark. Bulwark stays are to be ar- ranged in line with transverse beams or local stiffening. The stays are to have sufficient width at deck level. If the deck is of sandwich construction solid core inserts are to be fitted at the foot of the bulwark stays. Stays of increased strength are to be fitted at ends of bulwark openings. Openings in bulwarks should not be situated near the ends of superstructures.

3. Where bulwarks on exposed decks form wells, ample provision is to be made to facilitate freeing the decks from water.

109. Bulkhead structures

1. Watertight bulkheads

The number and location of watertight bulkheads are to be in accordance with reqrirements in Ch 1, Sec 4.

2. Supporting bulkheads

Bulkheads supporting decks are to be regarded as pillars. The buckling strength is to be considered in each individual case.