Section 3 Shell envelope laminate

3.1.1 Except as otherwise specified within this Section, the scantlings and arrangements for the shell envelope laminate are to be determined in accordance with the procedures described in, or as required by Pt 8, Ch 3, 3 Shell envelope laminate for mono-hull craft, using the pressures from Pt 5 Design and Load Criteria appropriate to multi-hull craft.

3.2.1 The breadth, b _K, and thickness, t _K, of plate keels are not to be taken as less than:

k _t is as defined in Pt 8, Ch 3, 2.1 General.

3.2.2 In no case is the thickness of the keel to be less than that of the adjacent bottom shell laminate.

3.2.3 The width and thickness of plate keels are to be maintained throughout the length of the craft from the transom to a point not less than 25 per cent of the freeboard measured at the forward perpendicular (FP) above the deepest load waterline on the stem. Thereafter the keel thickness may be reduced to that required by Pt 8, Ch 3, 3.3 Stem plate 3.3.1 for the stem. Laminate tapers are to comply with Pt 8, Ch 3, 3.14 Local reinforcement 3.14.2.

3.2.4 Where the bottom shell is of sandwich construction the keel is to be formed by locally returning to single skin construction for a width as required by Pt 8, Ch 4, 3.2 Keel plates 3.2.1. The Rule thickness of keel is to comprise both the inner and outer skins of the adjacent bottom shell sandwich plus additional reinforcement as required. The distribution of reinforcement in way of the plate keel and sandwich bottom structure is to be in accordance with Figure 4.3.1 Single skin/Sandwich skin intersection detail. See also Pt 8, Ch 3, 3.2 Keel plate 3.2.4.

3.2.5 For large, novel, asymmetric hull form craft, or yachts with externally attached ballast keels, or where it is proposed to incorporate keels of the `bar' type the scantlings of the keel will be specially considered.

3.3.1 For all craft types, the minimum bottom outboard shell laminate thickness as required by the Rules is to be extended over the region as defined in Pt 8, Ch 4, 1.5 Symbols and definitions 1.5.2 for displacement and semi-displacement craft.

Figure 4.3.1 Single skin/Sandwich skin intersection detail

3.3.2 The bending moment assumed to be carried by the bottom outboard shell laminate is to be not less than that determined by Pt 8, Ch 3, 1.9 Plate and sandwich laminates 1.9.1, using the design pressure from Pt 5, Ch 3, 3.1 Hull structures or Pt 5, Ch 4, 3.1 Hull structures for non-displacement or displacement type craft as appropriate. This bending moment is to be applied to laminates of both single skin and sandwich construction in the determination of the panel scantling required by Pt 8, Ch 4, 3.3 Bottom outboard 3.3.3 and Pt 8, Ch 4, 3.3 Bottom outboard 3.3.5 respectively.

3.3.3 An estimate of the thickness of bottom outboard single skin laminate is to be determined from Pt 8, Ch 3, 1.13 Determination of properties and stresses for single skin plate laminates 1.13.1. The tensile and compressive stresses are to be determined for each ply of reinforcement in the proposed laminate using Pt 8, Ch 3, 1.13 Determination of properties and stresses for single skin plate laminates 1.13.3 and Pt 8, Ch 3, 1.13 Determination of properties and stresses for single skin plate laminates 1.13.4, see also LR's Guidance Notes for Calculation Procedures for Composite Construction. The allowable tensile and compressive stress limits indicated in Table 7.3.1 Limiting stress criteria for local loading are to be complied with.

3.3.4 In no case is the minimum thickness of single skin laminate to be taken as less than 5,5 mm.

3.3.5 An estimate of the stiffness E , the thickness of single skin laminate for outer and inner skins of the bottom outboard sandwich panel and the thickness of core material is to be determined from Pt 8, Ch 3, 1.14 Mechanical properties sandwich laminates 1.14.2 and Pt 8, Ch 3, 1.14 Mechanical properties sandwich laminates 1.14.9 respectively. The tensile and compressive stresses are to be determined for each ply of reinforcement in the proposed laminate using Pt 8, Ch 3, 1.14 Mechanical properties sandwich laminates 1.14.7 and Pt 8, Ch 3, 1.14 Mechanical properties sandwich laminates 1.14.8. The allowable tensile and compressive stress limits indicated in Table 7.3.1 Limiting stress criteria for local loading are to be complied with.

3.3.6 The amount of reinforcement in laminates that form the skins of a sandwich laminate is to comply with the requirements of Pt 8, Ch 4, 2.1 General 2.1.2.

3.3.7 Special consideration may be given to laminate thicknesses lesser than those required by Pt 8, Ch 4, 3.3 Bottom outboard 3.3.4 and Pt 8, Ch 4, 3.3 Bottom outboard 3.3.6, provided that all of the structural strength requirements of the Rules are complied with, a satisfactory water barrier is provided, see Pt 8, Ch 3, 2.3 Sandwich skin laminate 2.3.1, and the equivalent impact resistance is demonstrated as required by Pt 8, Ch 3, 2.8 Impact considerations 2.8.2.

3.4.1 The scantlings and arrangements for bottom inboard shell laminate are to be determined in accordance with the procedures described in Pt 8, Ch 4, 3.3 Bottom outboard using the bottom inboard shell design pressure from Pt 5, Ch 3, 3.1 Hull structures or Pt 5, Ch 4, 3.1 Hull structures for non-displacement or displacement craft as appropriate.

3.5.1 The side outboard shell is as defined in Pt 8, Ch 4, 1.5 Symbols and definitions 1.5.7.

3.5.2 For all craft types, the minimum side outboard shell laminate thickness as required by the Rules is to be extended over the region as defined in Pt 8, Ch 4, 3.5 Side outboard 3.5.1 for displacement and semi-displacement craft.

3.5.3 The bending moment assumed to be carried by the side outboard shell laminate is to be not less than that determined by Pt 8, Ch 3, 1.9 Plate and sandwich laminates 1.9.1, using the design pressure from Pt 5, Ch 3, 3.1 Hull structures or Pt 5, Ch 4, 3.1 Hull structures for non-displacement or displacement type craft as appropriate. This bending moment is to be applied to laminates of both single skin and sandwich construction in the determination of the panel scantling required by Pt 8, Ch 4, 3.5 Side outboard 3.5.4 and Pt 8, Ch 4, 3.5 Side outboard 3.5.6 respectively.

3.5.4 An estimate of the thickness of side outboard single skin laminate is to be determined from Pt 8, Ch 3, 1.13 Determination of properties and stresses for single skin plate laminates 1.13.1. The tensile and compressive stresses are to be determined for each ply of reinforcement in the proposed laminate using Pt 8, Ch 3, 1.13 Determination of properties and stresses for single skin plate laminates 1.13.3 and Pt 8, Ch 3, 1.13 Determination of properties and stresses for single skin plate laminates 1.13.4, see also LR's Guidance Notes for Calculation Procedures for Composite Construction. The allowable tensile and compressive stress limits indicated in Table 7.3.1 Limiting stress criteria for local loading are to be complied with.

3.5.5 In no case is the minimum thickness of single skin laminate to be taken as less than 5 mm.

3.5.6 An estimate of the stiffness E , the thickness of single skin laminate for outer and inner skins of the side outboard sandwich panel and the thickness of core material is to be determined from Pt 8, Ch 3, 1.14 Mechanical properties sandwich laminates 1.14.2 and Pt 8, Ch 3, 1.14 Mechanical properties sandwich laminates 1.14.9 respectively. The tensile and compressive stresses are to be determined for each ply of reinforcement in the proposed laminate using Pt 8, Ch 3, 1.14 Mechanical properties sandwich laminates 1.14.7 and Pt 8, Ch 3, 1.14 Mechanical properties sandwich laminates 1.14.8. The allowable tensile and compressive stress limits indicated in Table 7.3.1 Limiting stress criteria for local loading are to be complied with.

3.5.7 The amount of reinforcement in laminates that form the skins of a sandwich laminate is to comply with the requirements of Pt 8, Ch 4, 2.1 General 2.1.2.

3.5.8 Special consideration may be given to laminate thicknesses lesser than those required by Pt 8, Ch 4, 3.5 Side outboard 3.5.5 and Pt 8, Ch 4, 3.5 Side outboard 3.5.7, provided that all of the structural strength requirements of the Rules are complied with, a satisfactory water barrier is provided, see Pt 8, Ch 3, 2.3 Sandwich skin laminate 2.3.1, and the equivalent impact resistance is demonstrated as required by Pt 8, Ch 3, 2.8 Impact considerations 2.8.2.

3.6.1 The scantlings and arrangements for side inboard shell laminate are to be determined in accordance with the procedures described in Pt 8, Ch 4, 3.3 Bottom outboard using the side inboard shell design pressure from Pt 5, Ch 3, 3.1 Hull structures or Pt 5, Ch 4, 3.1 Hull structures for non-displacement or displacement type craft as appropriate.

3.7.1 The wet-deck is as defined in Pt 8, Ch 4, 1.5 Symbols and definitions 1.5.8.

3.7.2 The bending moment assumed to be carried by the wet-deck laminate is to be not less than that determined by Pt 8, Ch 3, 1.9 Plate and sandwich laminates 1.9.1, using the design pressure from Pt 5, Ch 3, 3.1 Hull structures or Pt 5, Ch 4, 3.1 Hull structures for non-displacement or displacement type craft as appropriate. This bending moment is to be applied to laminates of both single skin and sandwich construction in the determination of the panel scantling required by Pt 8, Ch 4, 3.7 Wet-deck 3.7.3 and Pt 8, Ch 4, 3.7 Wet-deck 3.7.5 respectively.

3.7.3 An estimate of the thickness of wet-deck single skin laminate is to be determined from Pt 8, Ch 3, 1.13 Determination of properties and stresses for single skin plate laminates 1.13.1. The tensile and compressive stresses are to be determined for each ply of reinforcement in the proposed laminate using Pt 8, Ch 3, 1.13 Determination of properties and stresses for single skin plate laminates 1.13.3 and Pt 8, Ch 3, 1.13 Determination of properties and stresses for single skin plate laminates 1.13.4, see also LR's Guidance Notes for Calculation Procedures for Composite Construction. The allowable tensile and compressive stress limits indicated in Table 7.3.1 Limiting stress criteria for local loading are to be complied with.

3.7.4 In no case is the minimum thickness of single skin laminate to be taken as less than 5 mm.

3.7.5 An estimate of the E , the thickness of single skin laminate for outer and inner skins of the wet-deck sandwich panel and the thickness of core material is to be determined from Pt 8, Ch 3, 1.14 Mechanical properties sandwich laminates 1.14.2 and Pt 8, Ch 3, 1.14 Mechanical properties sandwich laminates 1.14.9 respectively. The tensile and compressive stresses are to be determined for each ply of reinforcement in the proposed laminate using Pt 8, Ch 3, 1.14 Mechanical properties sandwich laminates 1.14.7 and Pt 8, Ch 3, 1.14 Mechanical properties sandwich laminates 1.14.8. The allowable tensile and compressive stress limits indicated in Table 7.3.1 Limiting stress criteria for local loading are to be complied with.

3.7.6 The amount of reinforcement in laminates that form the skins of a sandwich laminate is to comply with the requirements of Pt 8, Ch 4, 2.1 General 2.1.2.

3.7.7 Special consideration may be given to laminate thicknesses lesser than those required by Pt 8, Ch 4, 3.7 Wet-deck 3.7.4 and Pt 8, Ch 4, 3.7 Wet-deck 3.7.6, provided that all of the structural strength requirements of the Rules are complied with, a satisfactory water barrier is provided, see Pt 8, Ch 3, 2.3 Sandwich skin laminate 2.3.1, and the equivalent impact resistance is demonstrated as required by Pt 8, Ch 3, 2.8 Impact considerations 2.8.2.

3.7.8 The wet-deck laminate on the underside of the cross-deck structure may require to be additionally protected, particularly where the air gap is small and there is a high risk of localised impact due to collision with floating debris, ice, etc. in the service area. In such cases the requirements for sheathing, given in Pt 8, Ch 3, 2.9 Sheathing, are to be complied with.

3.8.1 The scantlings and arrangements of transoms are to be not less than as required for the adjacent bottom inboard or side outboard structure as appropriate.

3.8.2 Where water jet or sterndrive units are fitted, the scantlings of the plating in way of the nozzles and connections will be specially considered.

3.9.1 For craft above 30 m in length, L _R, the stresses in the haunch area are to be derived using a two dimensional fine mesh finite element analysis. The model is to extend horizontally into the box structure and vertically into the strut structure. All discontinuities and cut-outs are to be modelled in order to determine shear stresses at critical locations and stresses for the determination of fatigue strength.

3.9.2 Due consideration is to be given to shear lag when calculating the effective breadth of the attached laminate.

3.10.1 Where the lower hull structure incorporates ring frames and attached shell laminate fitted between bulkheads or diaphragms, the thickness of the lower hull shell laminate may be derived from an established method for shell analysis or recognised standard for pressure vessels. Modes of failure to be considered are buckling, frame collapse, inter frame shell collapse and overall frame shell collapse between bulkheads. Copies of direct calculations are to be submitted for consideration.

3.10.2 In general the design load to be used is the pressure load given in Pt 5, Ch 4, 3.1 Hull structures. If other loads are considered to be of significance for the scantling determination these are to be taken into account.

3.11.1 Where the Rules do not specifically define the requirements for laminate elements with novel features then the scantlings and arrangements are to be determined by direct calculations. Such calculations are to be carried out on the basis of the Rules, recognised standards and good practice, and are to be submitted for consideration.