There is no doubt that space constraints are leading ports to demand taller RTGs to enable denser stacking of containers. There were over 640 RTGs scheduled for delivery in the last twelve months and manufacturers' feedback shows that one-over-five units account for around 65% of these orders. Less than 13% of orders were for one-over-four units and the trend looks set to continue. One-over-six and one-overseven units already account for around 10% and 6% respectively, though it is interesting to note that the majority of these are produced by ZPMC for its blossoming Chinese domestic port market.