Container Crane

Overview

A ship-to-shore container crane is the large rail-mounted gantry that loads and discharges containers between a vessel and the quay at a port terminal. The crane straddles the wharf on portal legs, reaching out over the ship on a cantilevered boom. A trolley runs the length of the boom and girder carrying a spreader, which locks onto a container's corner castings, lifts it, and traverses it ashore. Modern STS cranes work on a roughly 90-second cycle and handle the full range of ISO box sizes, including twin-lift of two 20-foot containers at once.

The crane is built on the Steel Structure, the welded steel frame of legs, girder, A-frame and boom that carries all loads down to the wharf. The whole machine rolls along the quay on the Gantry Travel System system of bogies and rails. Load handling is performed by the Trolley, which carries the reeving for the Hoist System and feeds the Telescopic Spreader that engages the containers. Motion is regulated by the Electrical System system of VFD drives and PLC control, the operator works from the suspended Operator Cabin, and the Safety System provides overload, snag and anti-collision protection.

How it works

Quay-side high voltage is drawn through a motorized cable reel and stepped down by the crane transformer, then fed to variable-frequency drives that power every motion. To work a box, the operator traverses the trolley out over the target cell and lowers the spreader on the wire-rope hoist. The spreader telescopes to the container length and rotates its twistlock cones into the corner castings, sensed by limit switches confirming lock. The hoist drum spools in to lift, and spring-set disc brakes hold the load if power is lost. The trolley carries the box shoreward while load cells watch rope tension for overload and the snag-protection cylinders absorb any sudden fouling. The boom luffs up to clear vessels arriving or departing, and the entire crane gantries along the rails to align with successive bays of the ship.