But how is it possible to plan when we have ill-designed measures of productivity?
When a carrier wishes to add another port terminal to its schedule it has to find one with sufficient spare capacity to handle the cargo on the days that the customer wishes to call.
Let’s start with a ship designed for 12,000 teu – that is the nominal figure. The effective one is lower because of all sorts of issues related to fuel, accommodations, outsized cargo, over height and over long boxes which add up to reducing the capacity by some 10% to 15%.
No one is clear what the actual is, it depends on the cargo mix.
So 12,000 really means 10,000 assuming the cargo weighs 10 tonnes or less per teu, otherwise the ship weights out (the cargo weight reaches the tonnage carrying capacity of the ship before it reaches the teu capacity).
The terminal estimates its capacity on the basis of the number of cranes that can work the ship, the terminal equipment and the speed at which containers can be evacuated from the terminal in order not to run out of space.
Most European terminals charge by the move, irrespective of whether the box is 20, 40 or 45 foot long. In Asia and North America it is by size. So now we have 10,000 teu which is not the same as the number of boxes or moves.
Assuming that the mix is 25% 20ft and 75% 40ft, we end up with 6,250 moves which can take a variable time to unload depending on the number of cranes employed. This can be nearly five days with three cranes and under three days with five cranes. A big impact on berth space.
Now let’s bring on the planners to work out the meaning of capacity and setting benchmarks.