Nautical Term: Shell
Definition of Shell
A shell refers to the casing or housing of a block or pulley. This casing encloses the working parts of the block, while allowing the sheave or pulley wheel to revolve freely. For instance, in a sailing ship, the blocks attached to the mast or the yards are mounted in wooden blocks or pulleys. The casing of these blocks houses the sheave or pulley wheel. By allowing the sheave to revolve freely, the sail can be hoisted up the mast or spread out along the yards.
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