Cranes are believed to have been in use as early as 3000 BCE. The earliest of them, called ‘shadoof’, were used to lift water from lakes and rivers for irrigating farmlands in Egypt. It consisted of a pole with a bucket on one end that was counterbalanced on a fixed support.

The Simple Crane
In its simplest form, a crane consists of a lever and a pulley.

Cranes at a fixed angle, with a single arm, were used in the early days to lift heavy loads. These days, modern cranes that can work from a few degrees angle to a nearly perpendicular position that can lift very heavy loads can be found everywhere, from construction sites to warehouses to seaports.

Stationary as well as mobile cranes help to move cargo from one location to another easily. Generally, cranes are counterbalanced to prevent them from toppling forward with the weight being lifted. Some of them have projecting arms or legs that can be planted firmly to the ground to help maintain stability and distribute weight evenly.

How are Shipping Containers Loaded and Unloaded?
Cranes play a very vital role when it comes to lifting and stacking heavy objects in the port yard. They are also used to load heavy objects onto a ship.

If we take a gantry crane that is more common in seaports, it has a main supporting framework called the gantry, a boom or a long arm that goes over the ship with a spreader and a cabin suspended over the main framework from where the operator controls the crane. Here, the spreader is a movable clasp that is used to grip and lift cargo containers from and onto a ship.

Mobile cranes have trolleys that move on tracks along the quayside. There are rubber-tired gantry cranes as well. Containers are lifted from the ship and placed on truck beds or on the ground for reach stackers or forklift trucks to move them to their designated area. Port cranes are generally designed to lift weights ranging from 40 to 120 metric tons.

A mechanism called ‘spreader’ is used to attach and lock onto the four corners of a shipping container to lift it for loading or unloading. It locks onto the corner castings of a container using a twist lock mechanism.

Spreaders are designed to lift 20’, 40’, or 45’ containers. A single spreader can lift these containers separately or 2×20’ containers together. Double spreaders can lift single containers, 2×40’ or 45’, or 4×20’ containers in one move. Spreaders are used in different types of cranes to handle shipping containers.

A crane may be diesel-powered or powered by electricity. However, most modern cranes are electric-powered. Separate high-powered motors are used to move the boom, gantry, trolley, and hoisting mechanism.

The cranes used in seaports are generally classified as quay cranes and yard cranes. As their names suggest, quay cranes operate by the quayside, while yard cranes are found in the inner yards of the port.