A Ship-to-Shore (STS) crane, also known as a quay crane, is a large, specialized piece of equipment used in port operations to load and unload containers and cargo between a vessel and the quay. These cranes are typically found at container terminals and play a critical role in ensuring the efficient operation of ports, thanks to their superior speed in handling containers compared to other crane types.
STS cranes are designed to run on rails, moving along the length of the wharf to access different cargo holds on a ship. With continuous upgrades, they are now capable of handling a wide variety of container types. They can handle individual 45-foot, 40-foot, or 20-foot containers, and can also lift two 20-foot containers simultaneously (a capability known as twin-lift).
The STS crane is considered the backbone of modern container terminals. Along with RTG (Rubber-Tired Gantry) cranes, reach stackers, terminal tractors, container stacks (lines), and yard areas, it forms a specialized, high-performance internal logistics system. The ability to move containers and cargo from the ship (Point A) to the container stacks, yard, or external trucks (Point B) as quickly as possible provides a strategic advantage in the era of global commerce. Below is more information about the “heart” of the modern port industry—the STS crane.
The Main Frame Structure of an STS Crane
The frame of an STS crane, known as the gantry, consists of four legs that are driven on two rails arranged along the quay. A key characteristic of the STS frame is its ability to withstand massive loads that are constantly changing and unevenly distributed during cargo handling operations.
This requires a design that ensures the crane’s center of gravity always remains within the safe operating envelope, even when the spreader travels to its maximum outreach on the seaside boom while under load. Simultaneously, all mechanical components distributed across the frame must operate harmoniously, efficiently, and rapidly.
The Waterside Boom and Landside Girder System
For the crane to move cargo from the ship’s deck to the shore and vice versa, the system of a waterside boom and a landside girder is essential. The landside girder is the section of the beam located over the land, while the waterside boom is the section that extends out over the water.
The reason for this two-part design is to ensure safety when a ship is docking. The waterside boom can be raised (or “boomed up”) to a near-vertical position to avoid any potential collision with the vessel.
Additionally, booming up has another benefit: it extends the lifespan of the boom itself. With an outreach ranging from 40 to 70 meters, leaving the boom in a horizontal position would maintain a significant bending moment on its structure, which, over the long term, would adversely affect the steelwork.
The trapezoidal frame Structure
The A-frame is a steel structure designed to support and distribute the load of the waterside boom. It is the highest point of the main gantry and features numerous steel members extending out to connect with the landside girder and waterside boom, simulating the load-bearing, load-distribution structure of a cable-stayed bridge.
The Trolley
The working principle of an STS crane involves the close integration of mechanical and electrical systems. An STS crane has a trolley that runs along rails on top of the boom and girder. This trolley system is used to move the spreader outwards (towards the ship) or inwards (towards the shore) to transfer containers. The crane cabin is also mounted directly on the trolley to ensure that the crane driver can best observe the lifting and lowering process.
The Spreader
The spreader is connected to the trolley, allowing it to move freely along the beam system to transfer containers between the ship and the shore. The spreader is also connected to the hoist system to lift and lower containers.
Modern spreaders are designed to increase handling productivity. The most common features include a telescopic capability to adjust its size for different container types and a mechanism for twin-lifting two 20-foot containers at once. They are also equipped with corner guides, known as flippers, to help align the spreader with the container, and a rotation system (slewing) to grab containers when the container or ship is not parallel to the quay.
Power Cable and Electrical System
An STS crane requires energy to operate. This energy is electrical power, supplied either through a power cable connected to the port’s three-phase electrical grid or by an on-board diesel generator. The generator ensures the crane can continue to operate during a port-side power outage.
Typically, the power supply for an STS crane uses medium voltage, ranging from 10kV to 22kV, fed directly from the quay. This power is then stepped down by an on-board transformer to operate the various equipment on the crane. The use of medium voltage helps reduce the size of the power cable and enhances operational safety.
The power cable is managed by a cable reel system and laid in a steel trough that runs along the crane’s rails. As the crane moves, sensors detect the cable’s tension and slack, as well as the crane’s direction of travel. This information is used to control the cable reel motor to either wind or unwind the power cable, preventing it from unspooling uncontrollably or becoming too taut and breaking.
In addition, the crane is equipped with numerous sensors, cameras, and other devices to assist the operator in maneuvering easily, safely, and accurately during cargo handling.
