Section 2 Hull girder strength for mono-hull craft

2.1.1 Longitudinal strength calculations are to be submitted for all craft with a Rule length, L _R, exceeding 40 m, covering the range of load and ballast conditions proposed, in order to determine the required hull girder strength. Still water, static wave and dynamic bending moments and shear forces are to be calculated for both departure and arrival conditions.

2.1.2 For craft of ordinary hull form with a Rule length, L _R, less than 40 m, the minimum hull girder strength requirements are generally satisfied by scantlings obtained from local strength requirements. However, longitudinal strength calculations may be required at LR's discretion dependent upon the hull form, constructional arrangement and proposed loading.

2.1.3 Where the Rule length, L _R, of the craft exceeds 65 m, or for new designs of large, structurally complicated craft, the design loads and scantling determination formulae in this Chapter are to be supplemented by direct calculation and structural analysis by 3-D finite element methods. These supplementary calculations are to include the results of model tests and full scale measurement where available or required by LR. Full details of such methods and all assumptions and calculations, which are to be based on generally accepted theories, are to be submitted for appraisal.

2.2.1 The effective geometric properties of the midship section are to be calculated directly from the dimensions of the section using only the effective material elements which contribute to the global longitudinal strength. For the purposes of this analysis an element may be a deck plating, longitudinal girder, inner bottom, etc. or other continuous member.

2.2.2 The distance of the neutral axis, y _NA, from the outer surface of the keel plate laminate may be determined from the following:

2.2.3 The resultant compressive stress within an individual ply, i, may be determined from the following:

2.2.4 The resultant tensile stress within an individual ply, i, may be determined from the following:

2.2.5 The ultimate tensile and compressive strengths of the laminate or face reinforcement which form an element, may be determined from suitable tests or alternatively may be predicted using classical stress/strain relationships with due account being taken of the amounts of different materials and their associated strain rates to failure. In this respect materials which are incompatible in terms of their strain rates to failure are not to be mixed. Where materials are mixed the requirements of Pt 8, Ch 6, 2.2 Bending strength 2.2.6 for reserve factors are to be complied with when a first ply failure analysis is carried out.

2.2.6 The allowable tensile and compressive stress limits indicated in Table 7.3.2 Limiting stress criteria for global loading are to be complied with.

2.3.1 The shear strength of the craft at any position along the length is to be examined. The shear stress, τ_H, is determined from the following:

2.3.2 The allowable shear stress limits indicated in Table 7.3.2 Limiting stress criteria for global loading are to be complied with.

2.4.1 Torsional stresses are typically small for ordinary mono-hulls less than 65 m in Rule length, L _R, and can generally be ignored.

2.4.2 The calculation of torsional stresses and/or deflections may be required when considering craft with unusual form or proportions, or with large deck openings. In general, calculations may be required to be carried out using a direct calculation procedure. Such calculations are to be submitted in accordance with Pt 8, Ch 6, 1.5 Direct calculation procedure.