cathead

A cathead is a small powered capstan or windlass mounted on the deck or frame of a ship, crane, or industrial hoisting structure. It consists of a rotating drum or spool driven by steam, hydraulic, or electric motor, around which rope or cable winds to provide pulling force for heavy loads. The drum diameter typically ranges from 300 to 600 mm depending on the load rating and rope size, and rotation speeds usually fall between 20 and 80 rpm for controlled load handling.

Catheads serve as auxiliary hoisting equipment, distinct from the main hoist or derrick system. They are commonly used to haul cargo over the rail of a vessel, tension mooring lines, or assist in rigging operations. The term originates from their mounting high on the ship's structure, literally at or near the "cat" davit (the framework that suspends lifeboats), though modern catheads are found wherever compact deck winching is needed. The equipment is sized to handle intermittent rather than continuous duty, typically rated for loads between 2 and 10 tonnes.

Operating principles and variants

A cathead requires manual rope feeding or a rope-laying mechanism to ensure the cable winds evenly on the drum. Older designs use brake bands or contracting brakes to control lowering, while modern units incorporate hydraulic or disc brakes with load-holding capability. The drum itself may be smooth or grooved; grooved drums grip rope better but require exact rope diameter matching. Most catheads drive the drum through a gearbox, reducing motor speed to produce useful torque.

Failure modes include rope slipping on a worn or dirty drum, brake fade under repeated load cycles, and shearing of the gearbox input shaft if shock loads are applied. Catheads are vulnerable to corrosion in salt-water environments, requiring regular paint maintenance and grease purging of bearings. Unlike the main hoist, a cathead operator relies heavily on hand signals and audible feedback to judge load position and tension, making clear communication essential on busy decks.

Catheads occupy a middle ground between manual tackle blocks and full-scale ship's cranes: they offer motorised pulling power at low cost and footprint, yet lack the precision and safety interlocks of larger hoisting gear. They remain common in older working vessels, fishing boats, and small shipyards where deck space and capital are limited. Modern equivalents include portable electric or air-powered chain hoists and hydraulic pull-lifts, which often replace traditional catheads in new construction.