Section 3 Longitudinal strength

3.1.1 The longitudinal strength is to be calculated for the condition when the ship of length L _s is supported on the keel blocks, the centre of the ship's length being over the mid-length of the dock, and the freeboard at the pontoon deck is at least equal to that given in Pt 2, Ch 1, 1.7 Freeboard 1.7.1.

3.2.1 Dock buoyancy distribution may be assumed rectangular over the length of the dock, L _D.

3.3.1 The weight curve of the ship can be taken as a rectangle, of length L_s, with a superimposed parabola of half the area of the rectangle.

3.4.1 The material to be included in the calculation of the section modulus will be, for the caisson type dock, all continuous fore and aft material, of the whole dock. For the pontoon type dock, all continuous fore and aft material of the wing walls structure may be included, together with the fore and aft material of the parts of the pontoon structure which are made effectively continuous by longitudinally scarphing the material into the adjacent pontoon for at least 2 m.

3.4.2 In no case should the crane rail be included in the section modulus calculation.

3.5.1 An approximate value of the sagging bending moment generated during docking of the ship can be obtained by the following expression:

3.5.2 Where it is intended that the normal operation of the dock is performed with ballast water evenly distributed over its entire length, the minimum required modulus in the bottom or upper deck of the floating dock can be obtained by the following formula:

3.5.3 Where provision is made for the normal operation of the dock to be complemented by the differential emptying of the ballast compartments, the required minimum section modulus can be obtained by the following formula:

However, for this type of operation of the floating dock, an efficient deflection control system is to be installed, see also Pt 2, Ch 1, 3.6 Deflection control system. The quantity and distribution pattern of water ballast intended for use during differential ballasting should be included in the Docking Operation Manual.

3.5.4 The maximum stress for the normal operation of the dock is not to exceed 137,34/K_L N/mm².

3.5.5 For pontoon type docks the minimum section modulus satisfying Pt 2, Ch 1, 3.5 Bending moment 3.5.2 or Pt 2, Ch 1, 3.5 Bending moment 3.5.3 will be required to be calculated in way of gaps between two adjacent pontoons. Mid-dock scantIings of fore and aft material for both pontoon and caisson type docks should be retained over the middle 0,4L_D. In the case of floating docks with relatively long pontoons, consideration will be given to a possible reduction of scantlings in areas well removed from the gaps.

3.5.6 The requirements set forth in Pt 2, Ch 1, 3.5 Bending moment 3.5.2, Pt 2, Ch 1, 3.5 Bending moment 3.5.3 and Pt 2, Ch 1, 3.5 Bending moment 3.5.4 are applicable to floating docks which are intended to be operated near the construction yard. In all other cases which involve ocean towage of the floating dock to the operational site, the minimum required section modulus is to be such as to ensure that the maximum stress en route does not exceed 170/K_L N/mm².

3.5.7 Where requested, use of LR’s computer programs are available to clients at an early stage of design development for prediction and the evaluation of the anticipated wave bending moment. For this service to be performed the following data should be submitted:

1. length of dock over pontoon/caisson;

2. breadth of dock;

3. draught in towage condition;

4. towage route;

5. departure date.

In all cases, the length of the wave will be taken as L _D and the wave height will be assumed equal to the maximum significant height to be expected during the voyage in tow.

3.6.1 Two completely independent deflection monitoring systems, preferably of different types are to be fitted.

3.6.2 Consideration will be given to acceptance of only one deflection control system for docks designed to operate without using differential ballasting.

3.6.3 It is recommended that one of the deflection monitoring systems required should be of the hydraulic type.

3.6.4 The deflection monitoring systems should be capable of outputting deflections over the entire length of the dock. The readings of one of the systems installed should be displayed in the control room of the dock.

3.6.5 In all cases, the methods of monitoring and limiting the dock deflections in service are to be submitted. In general, these methods are to include arrangements for visual and audible warning, and procedures for ballast control to prevent maximum allowable deflections being exceeded. The maximum allowable deflection should be related to the permissible still water bending moment.

3.7.1 Where specially requested, the structural design of the dock may be based on a ship length greater than that defined in Pt 2, Ch 1, 2.1 General 2.1.7. In such a case, the lifting capacities at the relevant L_S/L_D ratios are to be clearly stated during submission of plans.