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THE Top Tip – Six of Clubs – Reeving

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REEVING 

The magnifying power of sheave blocks is well understood and has been in use for centuries. In modern cranes, they are used to magnify the effect of the winches housed in the crane body. Without these, lifting of heavy loads of any size would be impractical as the winch and cable size would be huge.

However, the downside of this magnifying effect is the weight that must be added to the load being lifted. All the steel in the pins, retaining plates, and sheaves adds weight that must be supported by the boom and ballast weights before you add any lift load and rigging.

When reading the lift capacity charts of any crane, it must be remembered that these typically do not include the weight of the hook block which for large loads can be tens of tonnes in themselves. On marginal lifts this variance can be the difference between a crane lift plan working and not working.