Ship-to-Shore (STS) Container Crane Glossary: Key Terms and Components Explained
- CP&A Staff
- May 7
- 8 min read
Ship-to-shore container cranes are among the most iconic and essential machines in modern global trade, towering over ports as they efficiently transfer cargo between vessels and land. Yet, for newcomers and even industry professionals, the specialized terminology used to describe their components, movements, and operations can feel overwhelming at first. From technical jargon rooted in engineering to port-specific shorthand developed through decades of practice, understanding this language is key to navigating the world of container handling. This blog aims to demystify the vocabulary surrounding ship-to-shore cranes, providing a clear starting point for anyone looking to better understand how these massive machines function and communicate within the logistics ecosystem.
Container Crane Structural System
While there are a variety of different structural arrangements, this post will focus on the most common structural arrangements. The structural system has a rather unique set of names for the various components. Some terms are easy to understand like the legs, but others are not so obvious. The images below contain labels and names of structural beams for a typical quayside container crane.
Boom – The long horizontal arm that extends over the ship to lift containers
Trolley Girder – The fixed portion of the runway track that the trolley operates on. The trolley is stowed on the trolley girder when the boom is raised.
Boom hinge – Connection between the boom and trolley girder. The boom hinge allows the boom to be raised or lowered
Apex beam – Top of the triangular frame supporting the boom. This serves multiple purposes such as providing a lift point for the boom hoist, and the boom hinge for stowage. Also called a boom cross tie.
Legs – Vertical supports on each side of the crane
Sill beams – Horizontal members connecting the legs at the base.
Trolley girder support beams – Horizontal beams at the top of the O-frame. The trolley girder typically hangs from these beams. This beam is also often called the shoulder beam, transversal girder, or simply the upper beam.
Machinery house – Enclosure for motors and power transmission components. Most modern cranes have the main hoist, boom hoist, and trolley drive systems located in the machinery house. Sometimes the machinery house also includes the electrical house, which protects all the electrical components.
Trolley – Moveable unit carrying the head block and spreader. If there is an operator, the operator's cabin is typically attached the the trolley.
Headblock – Pulley assembly connecting hoist ropes to the spreader or cargo beam. Think of this as a universal connector that can attach to a spreader or cargo beam.
Spreader – Device that locks onto containers (often considered equipment but structurally integrated). Popular spreaders are capable of handling 40' containers, 45' containers, and twin 20' containers. Some spreaders are even capable of lifting tandem 40' containers!
Stow Pin – Structural anchoring system to secure crane in high winds. In some cases the anchoring system will also include tie-downs under the legs to prevent uplift.
Portal Beam – The portal beam is a horizontal member that braces the legs. It is elevated to allow equipment to pass under the portal beam and access or drop off containers. The portal beam is a very important component of the primary lateral force resisting system.
Cable reel – Subsystem that manages power supply cables.
Walkways, platforms, and ladders – Access structures and subsystems integrated into the crane
Handrails and guardrails – Safety-related structural components
Bracing members – Structural elements providing stiffness and stability. Bracing members can include the lower and upper diagonals. Cranes with larger outreaches typically have bracing between the two boom girders members.
Forestay – Tension rods supporting the boom in the down position. Many cranes have an inner and an outer forestay.
Backstay - Axial member that provides additional stiffness to the apex beam and trolley girder in the backreach.
Gantry Equalizers - This subsystem equalizes the wheel loads for a given corner. Typically half the wheels are driven which is why this subsystem is also commonly called the gantry travel system.
The actual arrangement of the main force resisting system will depend on the project requirements. For example there may be additional braces added between the legs if there are large lateral forces due to the cranes being located in a high wind or high seismic region. In some situations it makes sense to procure cranes with alternate arrangements such as a shuttle boom.
Optional Structural Features for Container Cranes
Some ports and terminal operators have special requirements that may require special structural systems.
Hatch-cover Platform
Hatch-covers are protective items used on container ships that serve several different purposes. Containers can only be stacked so high before the bottom container will fail. To allow larger vessels to stack containers higher they put a hatch-cover over the containers located under the deck of the vessel. This breaks up the container stack and uses the hull of the vessel to support the containers stacked above the deck.
Hatch-covers are typically stored in the back-lands after they are removed from the vessel. However, some crane operate on finger piers so the back-reach of the crane is over water. While the hatch-covers could be stored between the legs, this would block traffic from other port equipment such as bomb carts, straddle carriers, and top picks. A popular way to solve this potential issue is to have a hatch-cover storage platform on the crane. This way the crane can store the hatch-covers on the storage platform and not block operations.
Dual Trolley
A dual trolley arrangement has a second trolley at the portal beam level. The primary goal of this system is to increase the speed at which containers are offloaded from the vessel and transferred to the next part of the operation. The upper trolley serves the same purpose, it picks the containers off the vessel. Then the upper trolley places the container so that the lower trolley can pick it up and transfer it to the landside operation, typically a bomb cart, straddle carrier, or top pick.
Container Crane Mechanical System
The mechanical system has 4 primary axis of motion; the main hoist, boom hoist, trolley travel and gantry travel systems.
Main Hoist
The main hoist is the primary power transmission system. The crane's rated load indicates the lift capacity of the main hoist system. Most types of cranes have a main hoist, however STS cranes are unique in that the power transmission system is often located in the machinery house. Locating the power transmission system in the machinery house instead of on the trolley may sound strange, but the large cantilevers of modern ship to shore cranes change the design strategy. Minimizing the weight of the trolley becomes very important as the outreach increases.
Container cranes are rather unique as they have four independent hoist ropes to allow for trim, list and skew motions. This allows the operator to maneuver the spreader to land on a container that isn't perfectly positioned.
The largest main hoist systems can handle tandem 40' containers. There are two primary versions; single hoist and dual hoist. Single hoist has a special spreader that is capable of picking up two 40' containers. The dual hoist arrangement has two separate hoist systems with separate spreaders.
Boom Hoist
This system rotates the boom up and out of the way to make it easier for berthing. Berthing is when a container ship "parks". A large drum located in the machinery house pulls wire rope that is reeved to the apex beam and down to the boom.
Trolley Travel
They trolley travel system allows the trolley to move containers from the ship to the wharf. To get the weight of the trolley system as low as possible the STS trolleys are typically rope towed. Some trolleys are self propelled, which means the trolley travel machinery is located on the trolley.
Most trolleys are top running, meaning their wheels run on a rail. Some older cranes have underhung trolleys. Underhung trolleys have wheels that run on the bottom flange of a wide-flange beam. Underhung trolleys are rare for container cranes, but are more common in overhead electric traveling cranes (OET).
Catenary Trolley
For rope towed trolleys it is important to limit the cable sag. Limiting trolley rope sag improves performance. As outreaches became very large it was no longer practical to tension the trolley ropes for large spans. In addition to rope tensioning catenary trolleys support the trolley tow rope. By adding a support point the amount of rope tensioning is greatly reduced.
The main hoist system has the headblock and spreader which acts as an intrinsic rope tensioning system, so a separate tensioning system is not required for the main hoist system.
Gantry Travel
The gantry travel system allows the crane to travel along the length of the wharf. The gantry travel system consists of 4 sets of gantry equalizers, one per corner. To ensure an even load distribution the equalizer beams are hinged. It is common for each bogey (also called a two wheel truck), to contain one driven wheel and one idle wheel. Some applications require greater than 50% wheels driven.
Mechanical Terms
Bearings – Mechanical components that enable rotational or linear motion while minimizing friction and reducing wear between moving parts. They work by using rolling elements (balls/rollers) to replace sliding friction with low-friction rolling, or through sliding contact. Key types include ball, roller, and plain bearings, commonly used in automotive, industrial, and household applications.
Boom Hoist – The fixed portion of the runway track that the trolley operates on. The trolley is stowed on the trolley girder when the boom is raised.
Coupling – Mechanical components that join two rotary shafts to transmit power, torque, and motion, while accommodating misalignment or providing rigid alignment. They are crucial for connecting driving components (motors) to driven components (drums, gearboxes). Types include flexible (elastomer, gear, barrel, disc) for handling misalignment and rigid (sleeve, clamp) for precise alignment.
Checker's Cabin – Typically located under the sill beam near the stow pin. This is an enclosed workspace allowing a worker to monitor container options directly.
Energy Chain – A cable management system for the trolley. The enegry chain system connects the mobile trolley to the main power and communications supply in the machinery house. The cable chain sits in a tray which allows regular, repeatable, and predictable motion of the cable chain. This is an alternative to a festoon system.
Festoon – A cable management system for the trolley. A festoon system connects the mobile trolley to the main power and communications supply in the machinery house. Festoons systems have a series of cable trollies that support the electrical cables and maintain a reasonable amount of cable sag. This is an alternative to an energy chain system.
Headblock – Versatile component of the main hoist system that can support a container spreader, cargo beam, or other special lifting apparatus. Headblocks are commonly connected to specialized lift beams using twistlocks or pins.
Main Hoist – The long horizontal arm that extends over the ship to lift containers.
Operator's Cabin – Typically located on the trolley, this is where the operator sits and controls the crane. Remote operated and autonomous cranes may not have operator's cabins, but they can be useful for maintenance or as a backup operational method.
Sheaves – (pronounced "shiv") A grooved wheel used in pulleys to guide ropes, cables, or belts. Sheaves are the core component of a pulley system, designed to redirect force, manage motion, and reduce motor load. They are often used with wire ropes or belts.
Spreader – A special lift beam used to lift containers by 4 twistlocks, one at each corner. A spreader connects the the headblock. Popular spreaders telescopic which allows handling of 45', 40', or twin 20' containers. Larger spreaders can handle tandem 40' containers or even quad 20' containers.
Twistlock – Twistlocks, together with matching corner castings, form a standardized (rotating) connector system, for connecting and lifting shipping containers.
