Section 6 Rope and chain factors of safety

6.1.1 The safety factor required for ropes used to raise and lower the platform is to be not less than 3:1 based upon the certified breaking strength of the rope and the maximum rope tension. The maximum rope capacity is to be calculated from the rated capacity of the hoists with an allowance for the cumulative effect of sheave friction and wire rope stiffness of 1,5 per cent for ball or roller bearings and 5 per cent for plain or bushed bearings. Sheave friction and wire rope stiffness loss numbers derived from field measurements of similar shiplift equipment will be considered, provided data is from both new and existing shiplift installations.

6.1.2 For shiplifts with side transfer facilities where the platform is held on the ropes during side transfer, the rope capacity will need to be based on the maximum hoist reaction from the MDL during the side transfer operation.

6.1.3 It is recommended that, where side transfer operations take place or where docked vessels may remain on the platform for extended periods, consideration be given to a locking or suspension device to transfer the platform loads directly to the supporting structure.

6.2.1 The safety factor required for chains used to raise and lower the platform is to be not less than 3:1 based upon the certified breaking strength of the chain and the maximum chain tension. The maximum chain tension is to be based upon the rated capacity of the hoists.

6.2.2 In view of the possibility of stress corrosion cracking, grade 80 or a similar type alloy chain is not to be used.

6.2.3 Increased safety factors may be required where:

1. The hoisting speed of the platform exceeds 0,5 m/min.

2. The mode of operation of the hoist system may produce significant shock loading.

3. A less onerous inspection replacement programme than LR’s is envisaged in the case of installations certified but not classed.