Definition - What does Crown Block mean?
A crown block is a fixed set of pulleys at the top of the derrick of a drill rig over which the drilling line is threaded. The pulleys are assisted by travelling blocks that together are capable of hoisting heavy loads with the use of 3/4 inch to 1 1/2 inch diameter drilling line. Crown blocks help lift heavy loads even in rough weather conditions offshore when the drill vessel experiences heaving. Crown blocks are part of drill rigs that are used for oil and gas drilling operations.
Trenchlesspedia explains Crown Block
The crown block has two parts. The lower portion moves up and down in sync with the travelling block and is the main portion. The other portion is the two outer sheaves that are attached to the top of the piston rod which moves at exactly half the stroke of the crown block assembly through the chain reeving. This provides necessary rope compensation on dead and fast lines because insufficient rope compensation can lead to increased wear and degradation resulting from load variation.