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In sailing, a 'block' is a single or multiple pulley. One or a number of ''sheaves'' are enclosed in an assembly between ''cheeks'' or ''chocks''. In use a block is fixed to the end of a line, to a spar or to a surface. Rope or line is ''rove'' through the sheaves, and maybe through one or more matching blocks at some far end to make up a tackle.
The ''purchase'' of a tackle refers to its mechanical advantage. In general the more sheaves in the blocks that make up a tackle, the higher its mechanical advantage. The matter is slightly complicated by the fact that every tackle has a ''working end'' where the final run of rope leaves the last sheave. More mechanical advantage can be obtained if this end is attached to the moving load rather than the fixed end of the tackle.

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Sailing terms in everyday English

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Sailing terms in everyday English

; Chock a' block : Refers literally to the situation where pulling on the working line will not raise the load any further because the cheeks of one lifting block are already fast against the other. Figuratively this has come to mean that something is as full or as far as it can be.

See Also

★ Block and tackle

★ Two six heave