Block (sailing)

A line (rope) is reeved through the sheaves, and maybe through one or more matching blocks at some far end, to make up a tackle.

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.

Some blocks are used to increase mechanical advantage and others are used simply to change the direction of a line.

A single, large, sail-powered warship in the mid-19th century required more than 1,400 blocks of various kinds.

Several different types of block connections as used on sailing ships, including the regular shackle, upset shackle, reverse shackle, reverse upset shackle, swivel jaw, swivel eye made round or oval, loose front hook, loose swivel hook,stiff swivel hook, loose side hook, stiff front hook, and side sister hook.