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-
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.