How a container crane unloads a ship

A ship-to-shore crane straddles the quay with a long boom reaching over the ship. A trolley runs along the boom, and from it hangs a spreader that locks onto a container's four corner castings, hoists it, travels to the quay and lowers it onto a truck. Throughput is set by the cycle time: 3600 seconds in an hour divided by the seconds per move.

Controls

Labels

Animation speed

Cycle time per move

Spreader mode

Cranes working the ship

Step through it

Gantry on railsFour tall legs ride on rails along the quay, so the whole crane can shift to line up with any row of containers on the ship.
Boom and trolleyThe boom reaches out over the ship. A trolley runs along it, carrying the hoist ropes and the operator's cab out to the cargo and back.
The spreaderInstead of a hook, a spreader drops onto the box and twists locks into its four corner castings. In twin mode it grabs two 20 foot boxes at once.
Cycle time sets the paceEach move is hoist, travel, lower, release and return. Cut the cycle from 100 to 70 seconds and one crane goes from 36 to about 51 moves an hour.
Many cranes per shipBig ships are worked by several cranes side by side. More cranes shrink the time at berth, as long as the trucks can keep up.

Moves per hour

Terminals measure a crane by moves per hour: 3600 seconds divided by the average cycle time. A twin lift spreader carries two 20 foot boxes in one move, doubling the boxes for the same cycle. Ship productivity multiplies that by the number of cranes working the vessel.

This is a simplified teaching model. Real averages are lower than the ideal number because of hatch covers, lashing, waiting for trucks and repositioning the crane along the ship.

Try it: set one crane at 180 seconds per move in single mode. A 3,000 box exchange takes about 150 hours. Now try six cranes at 70 seconds in twin mode and it drops under 10.

Why the trolley path matters

The trolley travels farther to reach the outboard rows of a wide ship, which lengthens the cycle. That is one reason terminals invest in faster trolleys and longer outreach as ships get wider. The animation runs much faster than real time.

Sources

Container Cranes: Linking Ship to ShoreUniversity of Southern California, USC Sea Grant
Key Performance Indicator Development for Ship-to-Shore Crane Performance Assessment in Container Terminal OperationsJournal of Marine Science and Engineering (MDPI, open access)

How to cite this model

Avid Solutions International. (2026, November 11). How a container crane unloads a ship [Interactive 3D model]. Avid Field Lab. https://avidsolutionsintl.com/explore/container-crane

Last updated November 11, 2026

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