Section 7 Container securing arrangements for stowage using cell guides

7.1.1 Cell guide systems may be fitted to support containers stowed in holds or on exposed decks.

7.1.2 The cell guides are not to form an integral part of the ship’s structure. The guide system is generally to be so designed as to keep it free of the main hull stresses.

7.1.3 Cell guides are to be designed to resist loads caused by loading and unloading of the containers, to prevent shifting of the containers and to transmit the loads caused by motions of the ship into the main hull structure.

7.2.1 Cell guides are to be of robust construction and generally fabricated from steel plate and rolled sections. They are to have sufficient vertical extent and continuity to provide efficient support to containers. Guide bars are to be effectively attached to the supporting structure to prevent tripping or distortion resulting from container loading.

7.2.2 The intersection between cell guide and cross ties is to provide adequate torsional stability.

7.2.3 Intermediate brackets are to be fitted to vertical cell guides at suitable intervals.

7.2.4 The cell guides are to give a total clearance between the container and guide bars not exceeding 25 mm in the transverse direction and 40 mm in the longitudinal direction. The deviation of the cell guide bar from its intended line is not generally to exceed 4 mm in the transverse direction and 5 mm in the longitudinal direction.

7.2.5 Athwartship cross ties are to be fitted between cell guides at a spacing determined from the loading on the guides but, generally, not more than 3,0 m apart. Wherever possible, cross ties are to be arranged in line with the corners of the containers as stowed and are to be supported against fore and aft movement at a minimum of two points across the breadth of the hold. Where, however, the maximum fore and aft deflection in the cross tie can be shown not to exceed 20 mm, one support point may be accepted.

7.2.6 Longitudinal tie bars may be required to be fitted where shown necessary by the force calculations for the structure. Where fitted, they are to comply with the requirements of Pt 3, Ch 14, 7.2 Arrangement and construction 7.2.5.

7.2.7 Where, at the sides or ends of holds, the guide rails are fitted to transverse or longitudinal bulkheads, the bulkhead is to be locally reinforced to resist the additional loads.

7.2.8 If the carriage of 45 ft Euro containers complying with EU Directive 96/53 is specified to be carried in 45 ft cell guides, attention is to be paid to the arrangement of the corner castings, see Figure 14.7.1 45 ft euro container in cell guides. The guide bars need to be increased in order to ensure that a minimum design overlap, a, of 20 mm is achieved, taking into account the design clearances and tolerances defined in Pt 3, Ch 14, 7.2 Arrangement and construction 7.2.4. Consideration is to be given to the torsional loads being applied to the guide bars.

Figure 14.7.1 45 ft euro container in cell guides

7.3.1 Where the cell guides are arranged for the carriage of 40 ft containers, provision may be made for the installation of temporary intermediate cell guides for 20 ft containers. The permanent structure is to be designed such that it is suitable for either loading pattern.

7.3.2 Alternatively, permanent means for the support of 20 ft containers at the mid-length of a cell arranged for 40 ft containers will be considered. Such means may include the following:

1. A pillar (inboard) and vertical rest bar (on the longitudinal bulkhead) against which the container stack may rest. The pillar is to be supported laterally by the deck structure over and is to be sufficiently stiff to control lateral deflection of the container stacks.

2. Guide bars supported transversely by slim structure within the gap between containers and with longitudinal ties as necessary.

Details of proposals will be individually considered, taking into account the loads on the support structure and the resulting deflections.

7.3.3 Where it is desired to stow 20 ft containers without external support at the mid-bay location with or without 40 ft overstow, so-called ‘mixed stowage’ arrangements meeting the following requirements are applicable:

1. Maximum homogeneous container weights for 20 ft containers stowed in cell guides with no 40 ft container overstowed can be derived from Table 14.7.1 Maximum container weights of W_h 20 ft containers stowed in 40 ft cell guides with no overstow, depending on the transverse acceleration and the number of tiers in the stack.

2. Maximum homogeneous container weights for 20 ft containers stowed in cell guides with one or more 40 ft containers overstowed can be derived from:
   1. Table 14.7.2 Maximum containers weights, W_h of 20 ft containers stowed in 40 ft cell guides with overstow, diagonal stacking cone arrangement
   2. Table 14.7.3 Maximum container weights W_h of 20 ft containers stowed in 40 ft cell guides with overstow, other stacking cone arrangement
3. All inhold mixed stowage tables have been derived on the basis of all 20 ft containers having the same weight. However it is acceptable to carry non-homogeneous stacks provided the following two conditions are met:
   1. 20 ft containers heavier than specified in the weight W_h can be loaded provided that the average container weight excluding the lowest container in the stack does not exceed W_h, i.e.
      
   2. The total moment of 20 ft containers in a stacks about the base is not to be greater than the moment exerted by an equivalent homogeneous stack of weight W_h, i.e.
      

      where:

      W_i weight of container i.

      c_i height of container i.

      W_h is the homogeneous container weight as determined from Table 14.7.1 Maximum container weights of W_h 20 ft containers stowed in 40 ft cell guides with no overstow, Table 14.7.2 Maximum containers weights, W_h of 20 ft containers stowed in 40 ft cell guides with overstow, diagonal stacking cone arrangement or Table 14.7.3 Maximum container weights W_h of 20 ft containers stowed in 40 ft cell guides with overstow, other stacking cone arrangement as applicable. Where W_h is corrected by Note 5 of the tables, W_h is to be taken as W_hc.

      c_a average height of the 20 ft containers in the stack.

      N Number of 20 ft containers.

4. The weight of the lowest container in the stack may be increased to its rated value.
5. The force in the corner post in the lowest container is not to exceed the permissible compression value given in Table 14.9.6 Allowable forces in containers in stacks with the same base size. The force is to be determined by:
   

   where:

   V is the compressive force in the corner post

   W_40s is the total weight of the 40 ft containers, in tonnes

   W_20S-1 is the total weight of the 20 ft containers excluding the weight of the lowest container, in tonnes

   a_Z is the maximum vertical acceleration of all containers in the stack, see Pt 3, Ch 14, 8.2 Ship motion, wind and green sea forces acting on containers 8.2.5

6. Means are to be provided to prevent transverse sliding of the bottom of the stacks of 20 ft containers at the mid-bay position. This is to be in the form of permanently attached chocks at the inner bottom or equivalent. The design clearance is to be the same as for the cell guides and in accordance with Pt 3, Ch 14, 7.2 Arrangement and construction 7.2.4.

7. 20 ft containers stowed with no stacking cones are to be restrained to avoid transverse movement, e.g. all containers at the same tier height in a bay are to be of the same height and structural constraints between the containers and the hull are to be provided.

8. The 20 ft containers are to have closed steel walls and top (no open frame containers, e.g. tank or bulk containers).

Figure 14.7.2 Diagonal stacking cone arrangement

7.3.4 Alternative proposals for stowage arrangements will be individually considered and are to be accompanied by supporting calculations.

7.4.1 Analysis methods for the strength of the cell guide structure are to take due account of the interactive effects between guide structure and supporting deck structure and also of the deformation of the hull girder.

7.4.2 At its lower end the guide structure is to be efficiently connected to the deck structure. Cross ties are to be arranged between guides in a transverse direction at a spacing determined by the loading on the guides but in general not more than 3 m apart. Cross-bracing members of adequate strength and sufficient number are to be fitted in the transverse and longitudinal directions to prevent excessive deflection of the guide structure.

7.4.3 The height of guide bars above the deck is to be sufficient to ensure adequate restraint to the uppermost container tiers.

7.4.4 Where the cell guide structure is attached to highly stressed hull or deck elements, such as sheerstrakes, special attention is to be given to the design of the connection and the grade and quality of steel utilised.

7.5.1 A device to pre-centre the container and direct it into the cell guides is normally to be fitted at the top of the guide bars. Such devices include:

• fixed even peaks,
• fixed high and low peaks,
• ‘flip-flop’ systems,

but other devices will be considered. The device is to be of robust construction.