The maiden voyage of the 18,000 teu vessel Maersk Mc-Kinney Moller has been accompanied by much fanfare about record container handling productivity at various ports. Whilst it is generally true that larger vessels can facilitate faster port handling, the correlation between ship size and speed of port handling is not necessarily linear.
The move by all major carriers towards ever larger vessels in the pursuit of economies of scale is not automatically matched by similar advantages in terms of the speed of port handling. For shipping lines, what matters is turnaround time from vessel arrival to vessel departure – and essentially this means berth moves per hour across the ship. A key factor is gantry crane intensity across the ship, i.e. the maximum and average number of cranes deployed during the port call.
Vessel lengths are currently a critical factor in this respect. However, whilst teu intakes have been rising rapidly, the maximum length of vessels has not been increasing, only their height and width, making it harder to deploy proportionately more cranes. If and when ships of 22-24,000 teu are built, their length overall will be a key factor in port performance, therefore.
The number of cranes deployed for any particular vessel call also depends on numerous related factors. Importantly these cover not only operational issues, but also involve commercial choices.
As well as crane intensity, the other key factor in port turnaround times is moves per hour achieved per individual gantry crane. Here, there is often little difference whether the ship being handled is large or small – although the larger the ship, the longer the physical distance the crane trolley has to travel, both outwards across the vessel, and down into it. What is also influential is the speed of feeding containers to and from the yard and the crane – and this is largely a factor of the yard resources deployed. More tractor/trailers or straddle carriers per crane usually means faster individual crane performance – but this comes at a cost.
The criticality of crane intensity can be seen in the example below.
For the same size ship with the same size exchange of containers per call, and assuming that a turnaround time of around 24 hours is required, crane intensity makes a big difference. If seven cranes are deployed on average, each crane needs to achieve around 26 moves per hour. However, if only five cranes are deployed, each crane has to achieve an average performance more than 40% higher (37 moves per hour).
Container handling productivity is clearly influenced by ship size, with larger ships generally facilitating faster handling. However, there are numerous operational and commercial factors, in particular crane intensity, which also influence vessel turnaround times, so it should not be assumed that bigger ships will automatically lead to faster port turnarounds.
Source: Drewry Maritime Research