ABSTRACT
Loading ships as they are unloaded (double cycling) can improve the efficiency of a quay crane and therefore a container port. This chapter describes the double-cycling problem, presents solution algorithms to the sequencing problem, and provides simple formulae to estimate benefits. We focus on reducing the number of operations necessary to turn around a ship. First an intuitive lower bound is developed. We then present a greedy algorithm that was developed based on the physical properties of the problem and yields a tight upper bound. The formula for an upper bound on the greedy algorithm’s performance can be used to accurately predict crane performance. The problem is also formulated as a scheduling problem, which can be solved optimally using Johnson’s rule. Finally, we consider the longer-term impact of double cycling on crane productivity and briefly discuss port operations. For this we use an even simpler 190double-cycling algorithm that is operationally convenient, easy to model, and nearly optimum. A framework is developed for analysis, and a simple formula is developed to predict the longer-term impact on turnaround time. The formula is an accurate predictor of performance. We demonstrate that double cycling can create significant efficiency gains.
