Information Technology Reference
In-Depth Information
has a particular setup that involves two types of machines: Quay Cranes (QCs) and
Straddle Carriers (SCs). Quay Cranes (“Crane” in Figure 1) are able to move along
the shore and can load containers from the apron to the ship, or unload them from the
ship to the apron. Straddle Carriers are mobile cranes, able to move freely within the
container terminal. They are able to lift containers and stack them up to a certain height.
Given these areas and machines, the basic process of unloading a ship is as follows.
Containers are unloaded from the ship to the apron by the QC. While this is being done,
Straddle Carriers are clearing the apron by transporting containers from the apron to
the yard, and stacking them. The process for loading a ship is the reverse. This process
sounds fairly simple, but is made complicated by a range of factors and constraints. For
instance:
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There may be more than one QC operating on a given ship, so SCs need to be
shared between the QCs. Additionally, two QCs operating on the one ship need to
maintain a safe separation distance.
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When retrieving containers from the yard, the container needed may be beneath
other containers, which requires these containers to be moved in order to access the
desired container. It is worth noting that yard space is limited, and that container
terminals sometimes operate at a high level of yard capacity utilisation, so that one
cannot avoid stacking containers in a sub-optimal way.
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Some containers are refrigerated (“reefers”), and these cannot be without power for
an extended period. Additionally, for safety reasons, humans and machines cannot
be in the same area at the same time. Since (dis)connecting reefers to power is done
by humans, but moving reefers is done by machines, meeting the safety and power
constraints requires coordination.
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Issues may arise during operations such as machines breaking down, or finding
that certain containers cannot be stacked on top of certain other containers. Finally,
Straddle Carrier operators are human and may make mistakes in data entry. This
may lead to situations such as a later driver attempting to pick up container C1
from the yard, only to find that C1 is not where it is meant to be.
Note that the ship arrival times follow a known schedule, but that for various reasons
they sometimes do not follow this schedule. Planning of unloading can be partially done
before a ship arrives, but may need to be redone because the ship docks with reversed
orientation due to tides, or to accommodate dealing with trains and trucks.
The key metric for container terminal efficiency is ship turnaround time: any delays
to a ship's schedule are bad (and may involve a financial penalty to the port, if it fails
to meet the contracted service level agreement with shipping companies). Two key de-
cisions that the terminal operators need to make as part of day-to-day operations, and
which we have focussed on, are:
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How should SCs be allocated between QCs, yard rearrangement operations, and
trucks and trains? The management of straddle carriers has a big impact on the
terminal's efficiency. If QCs are not adequately served, then they may need to wait
for containers to be moved, which delays ship loading/unloading.
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Where should a given (incoming) container be placed in the yard? The placement of
containers in the yard can make a big difference to the cost of moving the container
later to where it is needed.
