Problems in Container Terminals

Problems in Container Terminals

This Post describes problems in container terminals. The main functions of these terminals are delivering containers to consignees and receiving containers from shippers, loading containers onto and unloading containers from vessels and storing containers temporarily to account either for efficiency of the equipment or for the difference in arrival times of the sea and land carriers. Containers are usually handled in two important compartments. We shall first describe what the compartments are, including the equipment involved in them. Then, the operations in container terminal are disclosed. After that, main decisions in the container terminal are defined. These decisions are subdivided into five scheduling problems.

Compartments

The first compartment is Yard-Side, which sometimes is referred to as Storage Area or Stacking Lane . In any container terminal, storage yard serves as temporary buffers for inbound and outbound containers. Inbound containers are brought in the port by vessels for import into land, whereas outbound containers are brought in by trucks and for loading onto vessels in order to export. A large scale yard may comprise a number of areas called zones . In each zone, containers are stacked side by side and on top of one another to form rectangular shape, which is called block

There is expensive equipment in the storage area for container handling, which is referred to as Rubber Tyred Gantry Cranes (RTGCs) . A RTGC can be seen across the block from the front-left to the front-right, while it is unloading a container from a truck. The efficiency of yard operations often depends on productivity of these RTGCs and their deployment. To balance the workload among blocks, RTGCs are sometimes moved between blocks so that they can be fully utilized.


To move between blocks , an RTGC has to make a 90-degree rotation (of its wheels) twice to move from one block to another. Since RTGCs are big in size and slow in motion, their movements demand a large amount of road space in the terminal for a non-trivial time period. Furthermore, any RTGC movement from one block to another takes time, and will result a loss in productivity of the RTGC.

The second compartment in the container terminal is Quay-Side. Usually, Quay-Side consists of a limited number of berths, each of which is equipped by several Quay Cranes (QC). The cranes are used to unload containers from vessels of the wharf and load containers to vessels. The cranes are usually flexible to be moved from a berth to another. A Typical QC, while it is unloading containers from a vessel to put it down on the truck in order to transport to the storage area.

Berths are essential resources in the container terminal. Therefore, with a high traffic of vessels, it would be ideal to have optimal allocation of berths to vessel to prevent undue delays of vessel in the terminal. At any time, only one ship can be docked at a berth.

Operations

The main operations in the port start by ship’s arrival. After a ship is berthed, it invokes a number of delivery requests for discharging. There are some vehicles in a terminal, which are usually Automated Guided Vehicles (AGV), or Internal Trucks (IT) Idle vehicles are dispatched according to the unloading request list to deliver containers from the berth to designated places in the storage yard. The QCs first unload containers from the containership and put them onto the vehicles. After that the vehicles carry the containers to designated storage area blocks and RTGCs unload the containers from the vehicles. Then the containers are put onto the yard stacks. In some terminals there is a number of Straddle Carrier, capable of loading, transporting and unloading of containers.

After the unloading phase of the ship, the loading phase will begin. On the landside, eXternal Truck (XT)brings in outbound containers before loading process of the relevant vessel, and they pick up inbound containers from the storage area or from the discharged vessel by QCs. The ship issues a number of loading requests. Vehicles are dispatched corresponding to the loading request list to deliver containers to the QCs. The operation is the reverse of the unloading process.

There are two major types of waiting lists in the port. The first one related to vehicles while the second one dedicated to the cranes. A vehicle has to wait if it has arrived at the crane's location but the crane is busy with other vehicles. A QC has to wait for a vehicle if it is ready to put a container onto a vehicle or to pick up a container from a vehicle but the vehicle has not arrived on the quay-side. Usually the cranes waiting time is more critical than the vehicle waiting time for efficiency of the terminal operations. Any delay in a quay crane operation will cause the same amount of time delay in all subsequent operations assigned to the same quay crane. This delay may even affect the ship's stay at the berth. Usually every ship has a time window and any delay lead to growing costs for the terminal. So one of the most important decisions in this system is allocation of quay cranes so that satisfy ship-timing window or minimize waiting times of the ships in the port.