Section 2 Longitudinal strength

2.1.1 Longitudinal strength calculations are to be made in accordance with the relevant requirements given in Pt 3, Ch 4 Longitudinal Strength, except as indicated in this Section.

2.2.1 Details are to be submitted of the following loading conditions for examination of longitudinal strength:

1. Homogeneous load conditions (including details of densities of spoil) for both departure and arrival at draught, T, and maximum dredging draught, T _m, where this exceeds T, see also Pt 4, Ch 12, 15.1 General 15.1.4.

2. Part loaded conditions (including details of densities of spoil) and ballast conditions for both departure and arrival.

3. Any specified non-homogeneous load conditions.

2.2.2 If any dredging equipment has to be unshipped, lowered or otherwise specially arranged or stowed before the ship proceeds on a sea-going voyage, this fact is to be indicated on the longitudinal strength information required to be submitted and is also to be clearly stated in the final Loading Manual supplied to the ship.

2.2.3 For loading conditions, and any other preparations required to permit ships with a notation specifying some service limitation to undertake a sea-going voyage, either from port or building to service area or from one service area to another, see Pt 1, Ch 2, 1 Conditions for classification.

2.2.4 Where a ship is arranged with two spoil spaces account is to be taken in the calculation of the still water bending moment of either one of these spaces being empty, unless such loading is specifically precluded in the Loading Manual supplied to the ship.

2.2.5 The requirements of Pt 3, Ch 4, 8.3 Loading instrument regarding loading instruments are not applicable to dredging and reclamation craft.

2.3.1 Hull bending strength standards are to comply with the relevant requirements of Pt 3, Ch 4 Longitudinal Strength, taking account of the contents of Pt 4, Ch 12, 2.4 Design vertical wave bending moments and Pt 4, Ch 12, 2.5 Permissible still water bending moment for dredging conditions.

2.3.2 For split hopper dredgers or barges, due account is to be taken of the lateral forces and moments on each half hull which are exerted by the pressure of the spoil and dynamic wave loading, see Pt 4, Ch 12, 17.2 Hull bending strength.

2.4.1 For the transit conditions at draught T, the design vertical wave bending moment at amidships, M_w, is to be determined from Pt 3, Ch 4, 5.2 Design vertical wave bending moments with the ship service factor, f₁, given in Table 12.2.1 Service factors f₁ and f_wd for ships with hopper or split hopper.

2.4.2 For the dredging conditions at draught T_m, the design hull vertical wave bending moment at amidships, M_wd, is given by the following expression:

where

• T_m is the dredging draught and is not to be taken less than draught, T
• M_wo is determined from Pt 3, Ch 4, 5.2 Design vertical wave bending moments, using C_bm in place of C_b
• f₂ is given in Pt 3, Ch 4, 5.2 Design vertical wave bending moments
• f₁ and f_wd are defined in Table 12.2.1 Service factors f₁ and f_wd for ships with hopper or split hopper.

2.5.1 The maximum permissible still water bending moment, , for dredging conditions where draught T _m exceeds T is not to exceed:

where M _wd is defined in Pt 4, Ch 12, 2.4 Design vertical wave bending moments 2.4.2.

Where applicable, the relevant loading conditions are to be included in the final Loading Manual, see Pt 4, Ch 12, 15.1 General 15.1.4 and Pt 3, Ch 4, 8.1 General.

2.6.1 The hull midship section modulus is to be calculated in accordance with the requirements of Pt 3, Ch 3, 3.4 Calculation of hull section modulus taking account of Pt 4, Ch 12, 2.6 Calculation of hull section modulus 2.6.2 and Pt 4, Ch 12, 2.6 Calculation of hull section modulus 2.6.3. See also Pt 4, Ch 12, 17.1 Symbols and definitions for split hull arrangements.

2.6.2 Centreline box keels within the hopper spaces may normally be regarded as 100 per cent effective provided that they are effectively scarfed to the vertical keels or equivalent structure at each end of the hopper spaces.

2.6.3 Where a long superstructure or deckhouse is fitted extending within the midship region, the requirements for longitudinal strength in the hull and erection will be specially considered.

2.7.1 Special attention is to be paid to the actual shear forces at the spoil space end bulkheads. The inclusion of the effective thickness of longitudinal bulkheads, centre box keel plating and other longitudinal material at these positions, will be considered in relation to the arrangement of structure proposed.

2.7.2 For ships classed A1 protected waters service, see Pt 4, Ch 12, 4.6 Side shell 4.6.1.

2.7.3 For transit conditions, the vertical wave shear forces, Q_w, are to be calculated in accordance with Pt 3, Ch 4, 6 Hull shear strength where the ship service factor, K₂, is taken as f₁, see Table 12.2.1 Service factors f₁ and f_wd for ships with hopper or split hopper.

where

• T_m is the dredging draught and is not to be taken less than draught T
• K is given in Pt 3, Ch 4, 6.3 Design wave shear force 6.3.1
• Q_wo is determined from Pt 3, Ch 4, 6.3 Design wave shear force using C_bm instead of C_b
• f_wd is defined in Table 12.2.1 Service factors f₁ and f_wd for ships with hopper or split hopper.