A polyspast is a heavy-duty hoisting device that uses a compound system of multiple pulleys to multiply lifting force. Designed for early construction and rigging, the arrangement routes a single continuous rope through several sheaves. Each additional loop of rope supporting the movable block increases the mechanical advantage, allowing a single operator to lift massive loads.
Heard on the job
We rigged a multi-sheave setup based on the polyspast principle to maximize our pulling force.
Insider tip
While the term belongs to classical mechanics, the exact same principle drives the multi-sheave tackle blocks used on heavy cranes.