Section 4 Extreme hull girder loads

4.1.1 The extreme hull girder loads specified in this section are applicable to all mono-hull naval ships for which the optional ESA1 or ESA2, Extreme Strength Assessment, notation is required. The design criteria detailed in this section are to be used in conjunction with the extreme hull girder strength assessment procedure given in Vol 1, Pt 6, Ch 4, 3 Extreme Strength Assessment, ESA

4.1.2 The extreme hull girder loads are typical lifetime maximum values that a ship is likely to encounter if it was to be present in an extreme sea state in sea areas associated with its service area notation.

4.2.1 The environmental design criteria for extreme design analysis given in Chapter 2 are to be used to determine the extreme hull girder loads.

4.2.2 The hull girder loads for the extreme hull girder strength assessment for unrestricted service operation, i.e. service area notation SA1, are typical maximum loads that are predicted for extreme winter North Atlantic conditions in head seas at low forward speed.

4.2.3 For other service area notations, the hull girder loads for the extreme hull girder strength assessment are typical maximum loads that are likely to be encountered within the restricted operational area.

4.3.1 For all mono-hull ships, the extreme vertical wave bending moment, M _WEX, at any position along the ship is given by:

4.3.2 Alternatively the extreme hull girder strength assessment wave loads may be derived using direct calculation methods, model tests or similar taking into account the likely range of wave periods and the environmental conditions specified in Vol 1, Pt 5, Ch 2 Environmental Conditions

4.3.3 In deriving the wave loads, the longitudinal distribution of the vertical wave bending moment is to taken in accordance with the longitudinal distribution factor, D _f, see Vol 1, Pt 5, Ch 4, 3.3 Vertical wave bending moments 3.3.1 Where appropriate, the hogging and sagging correction factor, F _fH and F _fS given in Vol 1, Pt 5, Ch 4, 3.3 Vertical wave bending moments 3.3.1, may be used to derive the hogging and sagging bending moments from a direct calculation.

4.3.4 If specified by the Owner, the extreme hogging and sagging vertical wave bending moment or extreme scaling factor, K _fEX, may be derived from long-term ‘in-service’ measurements from a series of ships with similar hull forms, mass distributions and areas of operation.

4.4.1 The extreme vertical wave shear force, Q _WEX, at any position along the ship is given by:

4.4.2 Alternatively the method of derivation of the extreme wave shear force may be consistent with that used to derive the bending moments.

4.5.1 Direct calculation procedures may be used to derive the extreme hull girder loads. LR’s calculation method of the extreme hull girder loads involves derivation of the short term maximum probable responses.

4.5.2 The extreme hull girder loads, M _WEX and Q _WEX, are to be based on the probable maximum values that are likely to be experienced during severe storms. The parameters of the severe sea state, i.e. significant wave height, wave period range and duration of storm, are given in Vol 1, Pt 5, Ch 2 Environmental Conditions.

4.6.1 The still water hogging and sagging shear force and bending moment distributions for the extreme hull girder strength assessment are to be taken as the Q _S and M _S distributions defined in Vol 1, Pt 5, Ch 4, 2.3 Still water shear forces and Vol 1, Pt 5, Ch 4, 2.2 Still water bending moments respectively.

4.7.1 The extreme hull girder strength design bending moment, M _REX, and associated shear forces, Q _REX, for all naval ships are to be determined as follows:

1. The extreme hull girder strength design bending moment, M _REX, is to be taken as (M _WEX + M _S), as defined in Vol 1, Pt 5, Ch 4, 4.3 Extreme vertical wave bending moments and Vol 1, Pt 5, Ch 4, 4.6 Still water shear forces and bending moments, taking into account the appropriate hogging and sagging conditions.

2. The extreme hull girder strength design shear force, Q _REX, is to be taken as (Q _WEX + Q _S), as defined in Vol 1, Pt 5, Ch 4, 4.4 Extreme vertical wave shear forces and Vol 1, Pt 5, Ch 4, 4.6 Still water shear forces and bending moments, taking into account the appropriate hogging and sagging conditions.

4.7.2 It is unnecessary to consider the effects of operating at high speed on the extreme design values for extreme hull girder strength. The requirements for bow flare impact global loads may be ignored in the derivation of M _WEX and Q _WEX.