Dr Emel Aktas

Is a sea change needed for the shipping industry?

Senior Lecturer in Logistics and Supply Chain Management | Cranfield School of Management

The world of container shipping is crucial to our everyday existence.  More than 60% of the goods we use every day are transported by sea.  This takes its toll on the environment.  Maritime transport accounts for approximately 3% of the world’s greenhouse gas (GHG) emissions and 4% of the EU’s total GHG emissions.

Many maritime companies have started lowering the speed of their ships (slow steaming) to help reduce fuel emissions.  However, reducing the environmental impact of the shipping industry is complex as there are many uncertainties around a ship’s journey at sea.  Adverse weather conditions can also have a big impact on journey times but also the time that a ship spends at each port on its journey can play a major part in delays and result in increased emissions.

Ships will visit many ports along their journey and the time they spend at each port loading and unloading cargo can vary from a couple of hours to more than a day.  The uncertainty around port timings is the result of less than perfect planning and communication systems that are used by port authorities across the world.

Vessels are given a time window for their arrival at a port.  As long as they arrive within this time window, they will meet their service objective.  If they arrive at the port earlier than their nominated time window, they will have to wait and if they are late, they will have to wait for a new slot.  This delay then results in ships increasing their speed in order to try and make up time to get to the next port in time.

The time windows allotted by ports can be very tight, especially when the ports are busy.  A good analogy can be made with the bullseye on a dartboard.  The smaller the target, the more difficult it is to hit.  The tight timescale at which a ship can dock at a particular port often leads to ships rushing to catch a nominated time window to achieve their set service targets.  The problem then is the faster a ship travels, the higher the emissions.

The issue of port times is less of a problem for transpacific or transatlantic journeys, as for these journeys the time spent at ports is a small fraction of the total time they spend at sea.  For longer journeys, the uncertainty of port times has relatively less impact on the service level since there is usually plenty of time at sea to make up for any delays incurred at ports.

For those ships with shorter journeys, a change in sailing speed may not always help, as the distance to be travelled to the next port is often not long enough to make up for the lost time incurred by port delays.  However, changing speed would help them if they were not so restricted by the arrival time window at their next port.

Based on extensive research with port operators and ship liners over the last two years, we have found that the length of the journey and the level of uncertainty around port times has an impact on the service levels that can be achieved by changing the speed of sailing.  This problem poses a trade-off between service levels and carbon emissions.  The uncertainty of port times results in speeding of ships, which leads to higher fuel consumption and higher carbon emissions.

Better coordination between ships and ports in terms of available time windows and likely disruptions to service will help both parties achieve higher service levels.  To achieve this, the port authorities must review the systems and technology they currently use for communication and scheduling of ships.  As the industry continues to grow, ports must adapt and innovate.  Out-of-date systems must be addressed in order to improve efficiencies and ultimately the industry’s impact on the environment.


Trade carried by sea has grown fourfold since 1970 and is still growing.  There are more than 100,000 ships at sea carrying all the solids, liquids and gases that we need to live.  The biggest container ship can carry 15,000 boxes and can hold 746 million bananas.  If the containers of the Danish company Maersk were lined up, they would stretch 11,000 miles, more than halfway round the planet.  If they were stacked instead, they would be 1,500 miles high, 7,530 Eiffel Towers!