The modern container shipping industry is booming because of the provision for faster voyages and less port stays. The major factor for this “quick work” is the introduction of the new types of gantry cranes in the market which is quicker and more reliable. This provides a great turnaround time for cargo operation at ports.
A container gantry crane is the biggest crane which is used in the operation sector of the shipping industry. It is designed for loading and unloading the container cargo from a container vessel.
The crane is operated by a specially trained crane operator from within the cabin located on the top end of the crane and suspended from the trolley. It is the operator who lifts the container from the ship or dock for unloading or loading of cargo. It is very important for both the ship and the shore staff (gantry operator, stevedores and foremen) to be alert and to maintain proper communication between them to avoid any accidents.
Basic Construction of Container Gantry Crane
Supporting Frame: The supporting frame is the giant structure of the crane which holds the boom and the spreader. For transverse movement of the crane in the jetty, frames can be rail mounted or moved by rubber tyres only.
Transverse operator cabin: It is incorporated in the bottom of the support frame, in which, a crane operator, for transverse movement of the crane in the yard, will sit and operate.
Boom: The boom of the gantry crane is hinged at the water side, so that it can be moved up and down as per the requirement of the cargo operation or navigation. For smaller gantry, where there is a fly zone located near the port, low profile booms are used which are pulled towards the gantry when off operation.
Spreader: Spreader is attached with the operator’s cabin on the rail structure and in the boom so that it can also move transversely on the boom for lifting cargo. The spreader itself can open and close depending upon the size and the number of containers to be lifted. The modern built spreader can lift up to 4 containers together.
Gantry operator cabin: Located at the top of the supporting frame, the cabin is 80 % transparent so that the operator can get a clear view of the loading and unloading operation.
The Basic Operation of Container Gantry Cranes
– For the loading operation, the stevedores remove the container lashing and the twist locks. Then as per the cargo plan, the selected container is discharged by a gantry crane.
– The spreader is lowered on top of the container, and it locks the four corners (corner castings) by a twist lock mechanism.
– Now the operator lifts the container and uses the transverse motion of the spreader to remove the container from the ship and load it over the truck in the shore platform.
– The gantry operator can lift up to 4 containers at a time, depending upon the type of gantry and size of containers.
– The loading of the container is done one by one as per the cargo plan, keeping the ship stability in mind.
– Normally truck and trailers bring the containers from the storage point to the gantry and spreader picks the container and loads it on the ship.
– Only one container is grabbed by the gantry crane for loading purpose as more precision is require to load the container, and aligning the hold guide and other containers.
The lifting capacity of gantry cranes may differ for different manufactures and this depends upon the size of the crane. The safe load lifting capacity is displayed clearly in the gantry structure.
The power source for gantry crane is from the shore electrical power supply or from diesel generator attached to the framework. Normally A.C shore power supply is used which may vary from 4000 to 13500 volts.