Pulley Block
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. 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. 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. There are various types of blocks that are used in sailing. Some blocks are used to increase mechanical advantage and others are used simply to change the direction of a line. A ''ratchet block'' turns fr ...
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Shipbuilding Cyclopedia 386
Shipbuilding is the construction of ships and other floating vessels. It normally takes place in a specialized facility known as a shipyard. Shipbuilders, also called shipwrights, follow a specialized occupation that traces its roots to before recorded history. Shipbuilding and ship repairs, both commercial and military, are referred to as "naval engineering". The construction of boats is a similar activity called boat building. The dismantling of ships is called ship breaking. History Pre-history The earliest known depictions (including paintings and models) of shallow-water sailing boats is from the 6th to 5th millennium BC of the Ubaid period of Mesopotamia. They were made from bundled reeds coated in bitumen and had bipod masts. They sailed in shallow coastal waters of the Persian Gulf. 4th millennium BC Ancient Egypt Evidence from Ancient Egypt shows that the early Egyptians knew how to assemble planks of wood into a ship hull as early as 3100 BC. Egyptian potte ...
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