Hydraulic crane

A hydraulic jigger is a hydraulically powered mechanical winch.

From the mid-19th century, hydraulic power became available throughout the increasingly modern dockyards and warehouses. This was generated centrally and distributed by pipework, either around a dock estate, or across a city by the new hydraulic power networks.

The jigger was developed by William Armstrong, around 1840, as part of his hydraulic crane The hydraulic crane was the invention that first made his fortune and established the engineering and armaments firm of Armstrongs of Elswick.

The jigger was one of the first hydraulic machines of the Victorian age, after Bramah's hydraulic ram but before the continuously-rotating hydraulic motor. It allowed the mechanism of the ram to be used to move over a usefully long distance, not merely the length of the ram.

A jigger works like a pulley block, but in reverse. Rather than turning an easy pull on a rope into a powerful lift, the jigger uses the powerful force of a hydraulic ram, but limited in how far it can travel, to pull a long length of chain. The chain is looped several times lengthwise around the ram cylinder, running over a number of pulleys at each end. When the cylinder moves, the pull on the end of the chain is multiplied by the number of loops. The force of the jigger's pull is reduced similarly, according to how many times the chain was looped. As the cylinder had adequate power to begin with, and could simply be made larger in diameter when needed, this was not a significant limit on the jigger's force.

Unlike cylinders, jiggers always provided a tension pull, rather than a compressive push.

The first jiggers pre-dated the development of flexible steel wire rope and so they used wrought iron chain, rather than the natural fibre rope otherwise available. Later machines did switch to wire rope.

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