Section 1 General
Clasification Society 2024 - Version 9.40
Clasifications Register Rules and Regulations - Rules for the Classification of Trimarans, July 2022 - Volume 1 Regulations and Structural Arrangements - Part 5 Environmental Loads - Chapter 4 Global Design Loads - Section 1 General

Section 1 General

Parent topic: Chapter 4 Global Design Loads

1.1 Introduction

1.1.1 The global design loads in this Chapter are to be used in conjunction with Vol 1, Pt 6, Ch 3 Global Strength Requirements to determine the global hull strength requirements. Unless otherwise stated, this Chapter is to be used exclusively for calculation of global loads for trimaran vessels and is to replace those global load calculations found in the Complementary Rules. For illustrations of global load cases, see Vol 4, Pt 1, Ch 2, 3 Load cases.

1.1.2 The global design load formulae in this Chapter are based on an x sh range of between 0,22L R and –0,06L R. Loads for values of x sh outside this range may need to be specially considered. x sh is defined in Vol 1, Pt 5, Ch 1, 1.4 Symbols and definitions.

1.1.3 Loads may be calculated directly according to the Load Development Procedure, see Vol 4, Pt 1, Ch 3 Load Development.

1.2 Information required

1.2.1 In order that an assessment of the longitudinal strength requirements can be made, the following information is to be submitted, in LR's standard format where appropriate:

  1. General arrangement and capacity plan or list showing details of the volume and position of the centre of gravity of all tanks, spaces and compartments.

  2. Bonjean data, in the form of tables or curves, for at least 21 equally spaced stations along the hull together with lines plan and/or tables of offsets.

  3. Details of the calculated lightweight and its distribution.

  4. Details of the weights and centres of gravity of all deadweight items for each of the main loading conditions.

  5. Calculated still water bending moments and shear forces and the proposed design envelopes. Calculated wave and dynamic bending moment shear force values.

1.2.2 It is recommended that this information be submitted in the form of a preliminary Loading Manual or Stability Information Book including: specification of operational requirements, hydrostatic data, details of loading conditions, etc. It may also be necessary to submit a summary of the damage stability analysis.

1.3 Direct calculation procedure

1.3.1 When utilising direct calculation procedures capable of deriving the wave induced loads on the ship, the ship's actual form and weight distribution is to be taken into account.

1.3.2 LR's direct calculation method of deriving the long term wave induced loads involves derivation of response to regular waves by strip theory, short-term response to irregular waves using the sea spectrum concept, and long-term response predictions using statistical distributions of sea states. This method is described in Vol 4, Pt 1, Ch 3 Load Development. Other direct calculation methods submitted for approval are normally to contain these three elements and produce similar and consistent results when compared with LR's methods.

1.3.3 The long term response predictions are to be based on a probability of exceedance of 10–8. The LR long term prediction method produces values which have a low statistical probability of occurring taking into account many factors. These factors include:

  • The operating life of the vessel. Normally the operating life is taken as 20 years which is assumed to correspond to 108 wave encounters.
  • The mission profile of the vessel.
  • Different loading conditions.
  • The effect of different wave headings on ship motions.
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