As containers move in and out of a waterside TZ, Expert Decking plans the container's placement and XPS monitors the slot's status. Expert Decking uses the following general strategy when selecting a slot for a container:
Export containers are prioritized to go close to the quay end of the TZ, and import containers are prioritized closer to an RMG stack.
XPS uses a pattern of 3,1,5,2,4 to select the row, using the first best slot within the row, starting at the center, and skipping adjacent slots to avoid potential straddle carrier conflicts.
In WSTZs, straddle and ASCs contend for the same space. This slot contention can lead to serious problems when an ASC needs to land a container and its slot has become occupied. To avoid this problem, straddle carriers try to refine possible problem slots twice:
When transitioning from Empty to Laden to Destination, if the destination stack is detected as being the same stack an ASC is currently dispatched to
When transitioning to Laden at Destination, if the destination stack is detected as a destination for a move that has been dispatched to an ASC
In both cases, ECN4 requests a position refinement from Expert Decking with the respective stack as a stack to avoid.
For more information on Expert Decking and using penalties, see Navis N4: Yard Manual.
Vessel Discharge operations
During vessel discharge operations, the move of a container from the vessel into an ASC block is split into two work instructions:
The first WI plans the container from the vessel to the waterside TZ.
The second WI plans the container from the waterside TZ into the ASC block.
To minimize the number of subsidiary plan updates, the actual vessel discharge event is planned in the composite timeframe only when all allocation ranges for the applicable allocation group are found within ASC blocks. The ASC Optimizer eventually recalculates the final planned positions prior to dispatching the second WI from the waterside TZ.