Section 1 General

1.1.1 The global design loads detailed in this Chapter are to be used in conjunction with Vol 1, Pt 6 Hull Construction in Steel to determine the global hull strength requirements. The application of the global design loads is given in Vol 1, Pt 6, Ch 4 Hull Girder Strength.

1.1.2 Flowcharts showing the procedures for the specification of the global design loads are shown in Figure 4.1.1 Procedure for the specification of global design loads.

1.1.3 The global design loads are divided into the following categories:

1. Hull girder loads.

   The types of hull girder loads which are to be considered for strength purposes in the initial design assessment are distinguished on the basis of their frequency of occurrence and are defined as follows:

   1. Still water shear forces and associated bending moments arising from static mass distribution and buoyancy forces, see Vol 1, Pt 5, Ch 4, 2 Still water global loads.

   2. Low frequency vertical wave shear forces and associated bending moments arising from hydrodynamic forces.

   3. High frequency dynamic shear forces and associated bending moments arising from slamming events.

   The derivation of the hull girder loads is given in Vol 1, Pt 5, Ch 4, 3 Global hull girder loads.

2. Extreme hull girder loads.
   The loads to be considered for extreme hull girder strength purposes are used to assess the hull girder structural capability to withstand extreme sea states. The derivation of the extreme hull girder loads is given in Vol 1, Pt 5, Ch 4, 4 Extreme hull girder loads.

3. Hull girder loads for residual strength assessment.
   The loads to be considered for residual strength purposes are used to assess the structural capability of the ship after damage to withstand moderately severe sea states. The derivation of the residual strength hull girder loads is given in Vol 1, Pt 5, Ch 4, 5 Residual strength hull girder loads.

1.1.4 Alternative methods of establishing the global load and design criteria will be specially considered, provided that they are based on model tests, full scale measurements or other generally accepted theories. In such cases, full details of the methods used and the results are to be provided when plans are submitted for approval.

1.2.1  L _R, B, B _WL, D and T are defined in Vol 1, Pt 3, Ch 1, 5 Definitions. F _n and Δ are defined in Vol 1, Pt 5, Ch 3, 1.3 Symbols and definitions 1.3.2 and Vol 1, Pt 5, Ch 3, 1.3 Symbols and definitions 1.3.1 respectively. Displacement mode and non-displacement mode are defined in Vol 1, Pt 5, Ch 3, 1.3 Symbols and definitions.

1.2.2 For longitudinal strength calculations of vertical shear force and bending moment, downward loads are to be taken as positive values and are to be integrated in the forward direction from the aft end of the ship. Shear force is positive when the algebraic sum of all vertical forces aft of the position is positive. Hogging bending moments are to be taken as positive values.

1.3.1 The still water longitudinal strength values are to be derived using a suitable longitudinal strength calculation system.

1.3.2 In direct calculation procedures capable of deriving the wave induced loads on the ship account is to be taken of the ship’s actual form and weight distribution.

1.3.3 Clasifications Register’s (hereinafter referred to as 'LR') direct calculation method of 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. 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.

1.3.4 The long term response predictions are to be based on probability 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.

1.4.1 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 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 a 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 and shear force values.

1.4.2 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.