Section 8 Strengthening requirements for beach landing operations

8.1.1 These requirements are in addition to those of Vol 1, Pt 6, Ch 3 Scantling Determination for bottom shell structure. They need only be applied to those areas of the hull at risk from grounding during beach landing operations. These areas are to be agreed with LR at an early stage in the plan approval process. A distinction is made between those areas likely to see impact loads on beaching and those where contact due to grounding will occur after the initial beaching.

8.1.2 The Rules assume that the ships will be brought into shallow water and up to the beach in a controlled manner and that procedures are in place and on board for the operation of these ships. The beach is assumed to be free of rocks of substantially greater projection than the depth of the rubbing strake.

8.1.3 Depending on the operational profile of the ship the minimum bow height given in Vol 1, Pt 3, Ch 2, 5.3 Minimum bow height and extent of forecastle will be specially considered.

8.1.4 Loading ramps are to be in accordance with the requirements of Vol 1, Pt 4, Ch 3, 5 Movable decks, lifts, internal and external ramps.

8.1.5 Due regard is to be given to forces imposed on the ship and loading ramps by ship motions in shallow water both by impact from surf, the beach, and vehicles used to manoeuvre ships on the beach.

8.2.1 For areas subject to impact and grounding the thickness determined from Vol 1, Pt 6, Ch 3 Scantling Determination is to be increased by 20 per cent and is in no case to be taken as less than 7 mm.

8.2.2 For operation in Arctic and Antarctic conditions the material grades are to be in accordance with the requirements of Vol 1, Pt 6, Ch 6, 2 Materials Material Class II.

8.3.1 Secondary stiffening is to be designed in accordance with the requirements of Vol 1, Pt 6, Ch 3 Scantling Determination with the modulus increased by 20 per cent. For impact areas the spacing of stiffeners is not to be greater than 500 mm.

8.3.2 Primary structure is to be designed in accordance with the requirements of Vol 1, Pt 6, Ch 3 Scantling Determination. An additional load case with the forces imposed from global bending and grounding forces uniformly distributed over the bottom in contact with the beach is to be considered. In the absence of specific information, not more than 50 per cent of the bottom structure is to be assumed to be in contact with the beach. The primary structure is also to be capable of supporting the concentrated loads imposed by loading or unloading vehicles.

8.3.3 Primary and secondary structure is to be continuously welded throughout areas subject to grounding.

8.3.4 Lugged connections or fully welded collars of the type shown in Figure 2.8.1 Collar arrangement are to be used. Alternative equivalent arrangements will be individually considered.

Figure 2.8.1 Collar arrangement

8.3.5 Transverse floors are not to be spaced more than 1,25 m for transversely framed structure or 1,85 m for longitudinal framed structure.

8.3.6 One side girder each side of the centreline is to be fitted in addition to the requirements of Vol 1, Pt 3, Ch 2, 3.5 Single bottom structure or Vol 1, Pt 3, Ch 2, 3.6 Double bottom structure.

8.3.7 Transverse floors and girders are to be suitably stiffened with web stiffeners spaced not more than 1,25 m apart.

8.4.1 For ships with L _R > 50 m grounding conditions in addition to the loading conditions of Vol 1, Pt 6, Ch 4 Hull Girder Strength are to be assessed. The number and type of loading conditions will be determined by the operational requirements of the ship. In some cases residual strength calculations will be required.

8.4.2 If L _R > 50 m and areas of the bottom shell within 0,3 to 0,5L _R are at risk from grounding the thickness of the bottom shell and longitudinal structure will be specially considered.

8.5.1 Rubbing strakes or barwhales are to be fitted to the bottom shell. In longitudinally framed ships they are to be placed directly below longitudinals. Typical arrangements of rubbing strakes are shown in Figure 2.8.2 Rubbing strakes. Usually they consist of a steel frame welded to the hull supports with a bolted connection to softer material but rubbing strips can be constructed of solid steel sections. They are to be free of projections or other discontinuities which could lead to damage of the shell plating.

Figure 2.8.2 Rubbing strakes

8.5.2 It is recommended that rubbing strakes are not to be spread more than 1,5m apart. For rubbing strakes spaced greater than 1,5m the bottom structure is to be specially considered.

8.5.3 The rubbing strake housing both internally and externally is to be efficiently coated to prevent corrosion. Where different materials are used the materials are to be selected or insulated to ensure that there is no galvanic corrosion.

8.5.4 Rubbing strakes are to be continuously welded to the hull. Butts between sections of rubbing strake are to be butt welded together before being welded to the hull. Where this is not possible, ceramic rather than copper backing strips are to be used.

8.5.5 Rubbing strakes are to be of the same grade of steel as the shell plate to which they are attached.

8.5.6 The ends of rubbing strakes are to be tapered at an angle of not less than 1 in 3 with no discontinuities in the welding in this region. Where not supported by internal longitudinals, the ends of strakes are to be arranged to pass 30 to 50 mm over the end of transverse frames or floors.

8.5.7 Due consideration is to be given to the depth of the rubbing strakes with regard to the nature of the beach. In no case are they to be less than 100 mm projection.