Section 3 Global hull girder loads

3.1.1 The global hull girder loads specified here are applicable to all displacement mono-hull naval ships as defined in Vol 1, Pt 1, Ch 2, 2.2 Definitions 2.2.7. These loads are to be used in the hull girder strength assessment given in Vol 1, Pt 6, Ch 3 Scantling Determination.

3.1.2 Individual consideration based on direct calculation procedures will generally be required for ships having one or more of the following characteristics:

1. Froude number > 0,8 (based on V _sp, see Vol 1, Pt 5, Ch 3, 1.3 Symbols and definitions 1.3.1)

   L _R/B _WL ≤ 5, or B _WL/D ≥ 2,5

   Unusual hull weight distribution

   Unusual type or design.

3.2.1 The environmental conditions given in Vol 1, Pt 5, Ch 2 Environmental Conditions are to be used in the derivation of the global hull girder loads.

3.3.1 The minimum value of vertical wave bending moment, M_W at any position along the ship may be taken as follows:

where

1. F_f is the hogging, F_fH, or sagging, F_fS, correction factor based on the amount of bow flare, stern flare, length and effective buoyancy of the aft end of the ship above the waterline.

2. F _fS is the sagging (negative) moment correction factor and is to be taken as

   FfS = –1,10 R A 0,3	for values of RA ≥ 1,0
   FfS = –1,10	for values of RA < 1,0

An area ratio value of 1,0 results in a sagging correction factor of –1,10.

1. F_fH is the hogging (positive) moment correction factor and is to be taken as
   
   
   R_A is an area ratio factor, see Vol 1, Pt 5, Ch 4, 3.3 Vertical wave bending moments 3.3.2.

3.3.2 The area ratio factor, R_A, for the combined stern and bow shape is to be derived as follows:

where

3.3.3 The bow flare area, A_BF, is illustrated in Figure 4.3.1 Deviation of bow and stern flare areas and may be derived as follows:

Alternatively the following formula may be used

L_f is given in Vol 1, Pt 5, Ch 4, 3.3 Vertical wave bending moments 3.3.1

For ships with large bow flare angles above the T_C,U waterline the bow flare area may need to be specially considered.

3.3.4 The stern flare area, A_SF, is illustrated in Figure 4.3.1 Deviation of bow and stern flare areas and is to be derived as follows:

where

3.3.5 Alternatively, for frigate and destroyer type ships the hogging and sagging vertical wave bending moments and shear forces may be derived from long term 'in-service' measurements of a series of ships with similar hull forms, mass distributions and areas of operation. Typically this will be based on a static wave balance approach. The longitudinal distribution of the vertical wave bending moment is to be taken in accordance with the longitudinal distribution factor, D_f.

3.3.6 The vertical wave bending moments and associated shear forces are not to be taken as less than that given by Vol 1, Pt 5, Ch 4, 3.3 Vertical wave bending moments 3.3.1 and Vol 1, Pt 5, Ch 4, 3.4 Vertical wave shear forces 3.4.1.

3.3.7 Direct calculation methods may be used to derive the vertical wave bending moments, see Vol 1, Pt 5, Ch 4, 1.3 Direct calculation procedures

3.3.8 The sagging correction factor, f_fS, in the vertical wave bending moment formulation in Vol 1, Pt 5, Ch 4, 3.3 Vertical wave bending moments 3.3.1 may be derived by direct calculation methods. Appropriate direct calculation methods may include a combination of long term ship motion analysis, non linear ship motion analysis and static balance on a wave crest or trough.

3.4.1 The wave shear force, Q _W, at any position along the ship is given by:

1. Positive shear force:

1. Negative shear force:

Intermediate values are to be determined by linear interpolation.

M _o, F _fH and F _fS are defined in Vol 1, Pt 5, Ch 4, 3.3 Vertical wave bending moments 3.3.1.

3.4.2 The direct calculation method used to derive the vertical bending moments may also be used to derive the vertical shear forces, see Vol 1, Pt 5, Ch 4, 1.3 Direct calculation procedures.

3.5.1 If considered necessary by LR, the effects of lateral bending moments may need to be considered. Normally this will only be required for ships with extreme hull forms, multihulls, unusual structural configurations or arrangements or particular loading conditions or operational modes which are likely to result in significant lateral stresses.

3.6.1 If considered necessary by LR, the effects of lateral shear forces may need to be considered. Normally this will only be required for ships with extreme hull forms, multihulls, unusual structural configurations or arrangements or particular loading conditions or operational modes which are likely to result in significant lateral stresses.

3.7.1 If considered necessary by LR, the effects of torsional moments may need to be considered. Normally this will only be required for ships with extreme hull forms, multihulls, unusual structural configurations or arrangements or particular loading conditions or operational modes which are likely to result in significant torsional stresses.

3.8.1 The requirements of this section are applicable to fast ships operating in the displacement mode that satisfy the following requirements:

1. speed V _sp > 17,5 knots

2. bow shape factor ψ > 0,15

3.8.2 For ships with knuckles in the bow flare region above which the hull is nearly vertical or exhibits tumblehome, the values of h _fr and A _b are normally to be based on the bow flare region below the knuckle
L _R and B _WL are as defined in Vol 1, Pt 5, Ch 4, 1.2 Definitions and symbols 1.2.1
V _sp is defined in Vol 1, Pt 5, Ch 3, 1.3 Symbols and definitions

3.8.3 The bow flare area is normally to be derived as follows:

see Figure 4.3.3 Derivation of bow shape.
L _R is given in Vol 1, Pt 5, Ch 4, 1.2 Definitions and symbols 1.2.1

3.8.4 The dynamic sagging bending moment due to bow flare impact loads, M _BF, is given by the following:

A _b is given in Vol 1, Pt 5, Ch 4, 3.8 Bow flare impact global loads 3.8.3
k _fr is given in Vol 1, Pt 5, Ch 4, 3.8 Bow flare impact global loads 3.8.1
L _R is given in Vol 1, Pt 5, Ch 4, 1.2 Definitions and symbols 1.2.1
It is not required to consider a hogging bow flare impact bending moment.

3.8.5 If the bow flare impact bending moment, M _BF, is greater than the wave bending moment, M _W, see Vol 1, Pt 5, Ch 4, 3.3 Vertical wave bending moments 3.3.1, at any position along the length then M _W is to be replaced by M _BF at these positions.

3.8.6 The bow flare impact shear force, Q _BF, associated with the bow flare bending moment is to be taken as follows over the forward half length of the ship:

where K _bf is to be taken as follows:
Positive shear force

Intermediate values are to be determined by linear interpolation.

Negative shear force

where

3.8.7 If the bow flare impact shear force, Q _BF, is greater than the wave shear force, see Vol 1, Pt 5, Ch 4, 3.4 Vertical wave shear forces, at any position along the length then the wave shear force, Q _W, is to be taken as Q _BF at these positions.

3.9.1 The requirements of this section are applicable to mono-hull ships when operating in the planing regime.

3.9.2 This section gives formulae for the derivation of the high frequency dynamic bending moment, shear forces and associated pressures. The bending moment and shear force values are to be used for the global design loads if they are greater than the values derived in accordance with Vol 1, Pt 5, Ch 4, 3.3 Vertical wave bending moments and Vol 1, Pt 5, Ch 4, 3.4 Vertical wave shear forces

3.9.3 The dynamic bending moment, due to a high speed planning craft landing on a wave crest amidships, at any position along the ship, is to be calculated using the following expression:

3.9.4 The non-dimensional vertical acceleration at the LCG, a_op, as defined in Vol 1, Pt 5, Ch 3, 2.4 Design vertical acceleration for ships in the planing regime, is not to be taken less than 1,0 for the purpose of determining the dynamic bending moment M _DW. If the values of a_bp and a_sp are unknown, the distributions given in Vol 1, Pt 5, Ch 3, 2.4 Design vertical acceleration for ships in the planing regime are to be applied.

3.9.5 Bottom longitudinals within 0,4L_R of amidships are subjected to the following effective pressure, P_ds:

3.9.6 Bottom plating within 0,4L _R of amidships is subjected to the following effective pressure, P _dp:

3.9.7 The dynamic shear force, Q _DW, at any position along the ship is given by:

3.10.1 The Rule bending moment envelope, M _R, and associated shear force envelope, Q _R, for use with the scantling determination procedures in Vol 1, Pt 6, Ch 3 Scantling Determination are to be determined as follows:

1. The Rule vertical bending moment envelope, M _R, is to be taken as (M_W + M_S), as defined in Vol 1, Pt 5, Ch 4, 3.3 Vertical wave bending moments and Vol 1, Pt 5, Ch 4, 2.2 Still water bending moments, taking into account the hogging and sagging conditions.

2. The Rule vertical shear force envelope, Q _R, is to be taken as (Q _W + Q _S), as defined in Vol 1, Pt 5, Ch 4, 3.4 Vertical wave shear forces and Vol 1, Pt 5, Ch 4, 2.3 Still water shear forces, taking into account the hogging and sagging conditions.

3.10.2 The values M _W and Q _W are to be replaced by M _BF and Q _BF if these are larger, see Vol 1, Pt 5, Ch 4, 3.4 Vertical wave shear forces and Vol 1, Pt 5, Ch 4, 3.8 Bow flare impact global loads 3.8.7 Similarly, the Values M _W and Q _W are to be replaced by M _DW and Q _DW if these are larger.