Ship's cargo pulley blocks (wire rope)

• Pages: 67-71

6. Ship's cargo pulley blocks (wire rope)

6.1. Single-sheave blocks

6.1.1. The safe working load of a single-sheave cargo block is

the maximum load that can be safely lifted by that block when it is

suspended by its head fitting and the load is secured to a wire rope

passing round its sheave.'

6.1.2. When a single-sheave cargo block is so rigged that the

load to be lifted is secured to its head fitting, the block being sus-

pended by the wire rope passing round its sheave,2 it should be

permissible to lift a load twice the value of the safe working load

marked on the block in accordance with the requirements of para-

graph 6.1.1.

6.1.3. The safe working load of a single-sheave cargo block

incorporated elsewhere in a derrick rig so that it is secured by its head

fitting and subjected to tension arising from a wire rope that forms

part of the derrick rig and passes round or partially round the sheave

is half of the resultant load upon its head fitting, due allowance being

made for the effects of friction in the block and rope stiffness (i.e. the

extra load arising from the effort of bending the wire rope partially

round the sheave).

6.1.4. The proof test load applied to a single-sheave block

should not be less than that indicated in Appendix paragraph D2. I.

6.2. Multi-sheave blocks

6.2.1. The safe working load of a multi-sheave block is the

maximum force that may be applied to its head fitting. In practice

this is the value of the resultant tension upon it when it is rigged in

the derrick, due allowance being made for the effects of friction in

the block and rope stiffness.3

1 See Appendix H, figure 1 and Appendix paragraph H.2.2.

2Appendix H, figure 2.

3 See Appendix H.

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