Section 3 Longitudinal strength

3.1.1 The following symbols and definitions are applicable to this Chapter, unless otherwise stated:

3.2.1 Longitudinal strength calculations are to be carried out for all ships where L _S is greater than 65 metres, covering the range of load and ballast conditions proposed, in order to determine the required hull girder strength. The calculations of still water shear forces and bending moments are to cover both departure and arrival conditions. See Pt 3, Ch 4, 5.3 Design still water bending moments 5.3.3 of the Rules for Ships.

3.3.1 In order that an assessment of the longitudinal strength requirements can be made, the information listed in Pt 3, Ch 4, 4.1 List of requirements of the Rules for Ships is to be submitted in LR’s standard format, where appropriate.

3.4.1 The symbols used in this sub-Section are defined as follows:

3.4.2 The requirements given in this Section are applicable to vessels with length L _S between 122 metres and 320 metres.

3.4.3 Longitudinal strength of the vessels with length L _S outside the limits given in 3.4.2 will be specially considered.

3.4.4 For operation in harbour waters a higher permissible still water bending moment can be assigned based on reduced combined vertical wave and springing moment, see Ch 4, 3.4 Hull bending strength 3.4.15.

3.4.5 The standard still water bending moment, M _U, hogging and sagging, is given by:

3.4.6 The hull midship section modulus about the transverse neutral axis, at the deck or the keel, is to be not less than:

or

The still water bending moment coefficient C is given by:

3.4.7 For materials to be included in the calculation of actual hull section properties, see Pt 3, Ch 3, 3.4 Calculation of hull section modulus of the Rules and Regulations for the Classification of Ships, July 2022.

3.4.8 Scantlings of all longitudinal members of the hull girder based on the minimum section modulus requirements given in Ch 4, 3.4 Hull bending strength 3.4.6 are to be maintained within 0,67L_S amidships for and above, and within 0,4L_s amidships for and below. Intermediate values are to be determined by linear interpolation.

3.4.9 The scantlings of all longitudinal continuous material may be tapered from the midship extremities as defined in Ch 4, 3.4 Hull bending strength 3.4.8, to the fore and aft ends of the ship. See also the relevant Sections within Pt 3, Ch 4 Longitudinal Strength Pt 3, Ch 3, 2.5 Taper requirements for hull envelope and of the Rules and Regulations for the Classification of Ships, July 2022 relating to taper and material outside of the mid-body section.

3.4.10 The design still water bending moment, M _L, hogging and sagging, is the maximum moment calculated from the loading conditions.

3.4.11 The design springing bending moment M _V is given by:

3.4.12 The design wave bending moment M _W is given by:

3.4.13 The maximum permissible combined stress (still water plus dynamic) for hull vertical bending, σ, within amidships region defined in Ch 4, 3.4 Hull bending strength 3.4.8 under the standard still water bending moment defined in Ch 4, 3.4 Hull bending strength 3.4.5, is given by:

For L_s/D = 17 and below:

between 0,3 L_s and 0,7 L_s from aft

For L_s/D = 21 and above:

between 0,165L_s and 0,835L_s from aft

Intermediate values are to be determined by linear interpolation.

Where d is the distance in metres, from the F.P. (for the fore end region) or the A.P. (for the aft end region), as appropriate, to the location under consideration.

Special consideration will be given to increasing the permissible stress outside 0,4L amidship to provided that sufficient buckling checks are carried out.

The actual hull vertical bending stresses at strength deck, σ_D, and keel, σ_B, are given by the following, using the appropriate combination of hogging and sagging bending moments to give sagging or hogging stresses:

and

3.4.14 The permissible still water bending moment, , is to be achieved in the maximum section modulus calculation. The permissible still water bending moment is not to be exceeded for all loading conditions. The permissible still water bending moments, sagging and hogging, are to be taken as the lesser of the following:

or

3.4.15 The permissible still water bending moments, sagging or hogging, in harbour for the draught under consideration are not to exceed the following value:

3.4.16 The hull midship section moment of inertia about transverse neutral axis is to be not less than the following:

for the vessels with length L _S equal to 122 metres and below

for the vessels with length L _S between 122 metres and 213 metres

for the vessels with length L _S equal to 213 metres and over

3.5.1 Shear strength requirements of the vessels with length L _S greater than 65 metres is to be investigated.

3.5.2 Shear strength of the vessels with length L _S between 122 metres and 320 metres is to be in accordance with this Section. Shear strength of the vessels with length L _S outside the limits given above will be specially considered.

3.5.3 For operation in harbour waters a higher permissible still water shear forces can be assigned based on reduced combined dynamic shear forces, see Ch 4, 3.5 Hull shear strength 3.5.8.

3.5.4 The following symbols are applicable to this Section, unless otherwise stated:

are as defined in Pt 3, Ch 4, 6.1 Symbols of the Rules and Regulations for the Classification of Ships, July 2022.

3.5.5 The design hull dynamic shear force, Q _W, at any position along the ship is to comply with the requirements of Pt 3, Ch 4, 6.3 Design wave shear force of the Rules and Regulations for the Classification of Ships, July 2022, except that Q _WO and K ₂ are to be taken as defined below:

3.5.6 The design still water shear force, Q _S, at each transverse section along the hull is to be taken as defined in Pt 3, Ch 4, 6.4 Design still water shear force of the Rules for Ships, as applicable.

3.5.7 The permissible hull still water shear force is to comply with the requirements of Pt 3, Ch 4, 6.5 Permissible still water shear force of the Rules for Ships. Value of Q _W used in calculations is to be taken as given in Ch 4, 3.5 Hull shear strength 3.5.4.

3.5.8 The permissible still water shear forces, positive or negative, in harbour or equivalent environment are not to exceed the following value:

3.5.9 The permissible combined shear stress τ (still water plus dynamic) is to be taken as:

3.5.10 The design shear stress is to comply with the requirements of Pt 3, Ch 4, 6.7 Design shear stress of the Rules for Ships. Value of Q_W used in calculations is to be taken as given in Ch 4, 3.5 Hull shear strength 3.5.4.

3.6.1 The requirements of Pt 3, Ch 4, 7 Hull buckling strength of the Rules for Ships are applicable within amidships section defined in Pt 3, Ch 4, 7.1 Application 7.1.2 of the Rules for Ships.

3.6.2 When carrying out buckling calculations the standard corrosion deduction ranges, d _t range mm, given in Table 4.7.1 Standard deduction for corrosion, d t of the Rules for Ships, are to be substituted as follows:

3.7.1 The requirements of Pt 3, Ch 4, 8 Loading guidance information of the Rules and Regulations for the Classification of Ships, July 2022 are to be complied with.

3.7.2 Where ballast water is carried in the cargo holds of non self-unloading bulk carriers, the sailing condition is to be included in the loading manual for approval, as per Pt 3, Ch 4, 8 Loading guidance information of the Rules and Regulations for the Classification of Ships, July 2022.

3.7.3 New ships to which the Load Line Regulations are applicable, will be assigned class, only after it has been verified that the level of intact stability is approved by the National Authority.

3.8.1 Hold mass curves are to be included in the Loading Manual and the Loading Instrument and cover any single hold and any two adjacent holds whilst in transit and during loading and unloading operations in harbour. The curves are to show the maximum allowable and minimum required cargo mass as a function of draught. The method adopted is based on the concept of retaining the same imbalance between cargo load and the buoyancy upthrust over the full draught range, and with the double bottom tanks empty.

3.8.2 Hold mass curves are to be prepared in accordance with LR ShipRight procedure Primary Structure of Bulk Carriers, May 2004, Section 8, as applicable to BC-B and BC-C, with no MP, ships.