Section 2 General

2.1.1 Longitudinal strength calculations are to be carried out for all ships where L is greater than 65 m, 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 and any special mid-voyage conditions caused by changes in ballast distribution.

2.1.2 For ships where L is equal to or less than 65 m, longitudinal strength calculations may be required, dependent upon proposed loading.

2.1.3 Specific information regarding required loading conditions is given in the individual ship type Chapters.

2.2.1 In general, where a long superstructure or deckhouse of length greater than 0,15L is fitted, extending within the 0,5L amidships, the requirements for longitudinal strength in the hull and erection will be considered in each case.

2.3.1 For ships other than container ships which have large deck openings and where the structural configuration is such that warping stresses in excess of 14,7 N/mm² are likely to occur, local increases in section modulus, based normally on the combined stress diagram undertaken for container ships, may be required. For calculations for container ships, see Pt 4, Ch 8, 3 Longitudinal strength.

2.3.2 For ships with large deck openings such as containerships, sections at or near to the aft and forward quarter length positions are to be checked. For such ships with cargo holds aft of the superstructure, deckhouse or engine room, strength checks of sections in way of the aft end of the aft-most holds, and the aft end of the deckhouse or engine room are to be performed.

2.4.1 In ships of length between 120 and 170 m and maximum service speed greater than 17,5 knots, in association with a bow shape factor of more than 0,15, the Rule hull midship section modulus and the distribution of longitudinal material in the forward half-length will be specially considered, see Pt 4, Ch 1, 3 Longitudinal strength.

2.5.1 In direct calculation procedures capable of deriving the wave induced loads on the ship, and hence the required modulus, account is to be taken of the ship's actual form and weight distribution.

2.5.2 Clasifications Register's (hereinafter referred to as 'LR') direct calculation method involves derivation of response to regular waves by appropriate sea keeping software, 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 should normally contain these three elements and produce similar and consistent results when compared with LR's methods.

2.6.1 Where the assumptions, method and procedures of a longitudinal strength calculation system have received general approval from LR, calculations using the system for a particular ship may be submitted.