Preface. Since 90% of international goods move by ships, I was curious about how much fuel they burned. It’s a lot: The very large container ship CMA CGM Benjamin Franklin above, which can carry 18,000 20-foot containers, carries approximately 4.5 million gallons of fuel oil, which takes up 16,000 cubic meters (FW 2020). As much fuel as 300,000 15-gallon tank cars.
But these ships can carry 200,000 tons of goods, so they end up being more energy efficient than 300,000 cars (Stopford 2010, UNCTAD 2012).
Pound for pound and mile for mile, today’s ships are the most energy-efficient way to move freight. Table 1 shows the energy efficiency of different modes of transport by kilojoules of energy used to carry one ton of cargo a kilometer (KJ/tkm). As you can see, water and rail are literally tons and tons—orders of magnitude—more energy efficient than trucks and air transportation.
Table 1 Energy efficiency of transportation in kilojoules/ton/kilometer (Smil 2013), Ashby 2015)
(A) ……………Transportation mode
50……………. Oil tankers and bulk cargo ships
100–150….. Smaller cargo ships
30,000…….. Air freight
(A) Kilojoules of energy used to carry one ton of cargo one kilometer Transportation mode
Alice Friedemann www.energyskeptic.com author of “When Trucks Stop Running: Energy and the Future of Transportation”, 2015, Springer, Barriers to Making Algal Biofuels, and “Crunch! Whole Grain Artisan Chips and Crackers”. Podcasts: Collapse Chronicles, Derrick Jensen, Practical Prepping, KunstlerCast 253, KunstlerCast278, Peak Prosperity , XX2 report
Fuel consumption by a container ship is mostly a function of ship size and cruising speed, which follows an exponential function above 14 knots. So an 8,000 TEU container ship consumes 225 tons of bunker fuel per day at 24 knots, but at 21 knots consumption drops to 150 tons per day, a 33% decline. While shipping lines would prefer consuming the least amount of fuel by adopting lower speeds, this advantage must be mitigated with longer shipping times as well as assigning more ships on a pendulum service to maintain the same port call frequency. The main ship speed classes are (Notteboom 2009):
- Normal (20-25 knots; 37.0 – 46.3 km/hr). Represents the optimal cruising speed a containership and its engine have been designed to travel at. It also reflects the hydrodynamic limits of the hull to perform within acceptable fuel consumption levels. Most containerships are designed to travel at speeds around 24 knots.
- Slow steaming (18-20 knots; 33.3 – 37.0 km/hr). Running ship engines below capacity to save fuel consumption, but at the expense a additional travel time, particularly over long distances (compounding effect). This is likely to become the dominant operational speed as more than 50% of the global container shipping capacity was operating under such conditions as of 2011.
- Extra slow steaming (15-18 knots; 27.8 – 33.3 km/hr). Also known as super slow steaming or economical speed. A substantial decline in speed for the purpose of achieving a minimal level of fuel consumption while still maintaining a commercial service. Can be applied on specific short distance routes.
- Minimal cost (12-15 knots; 22.2 – 27.8 km/hr). The lowest speed technically possible, since lower speeds do not lead to any significant additional fuel economy. The level of service is however commercially unacceptable, so it is unlikely that maritime shipping companies would adopt such speeds.
In an environment of higher fossil fuel prices, maritime shipping companies are opting for slow steaming for cost cutting purposes. The ongoing practice of slow steaming is likely to have an impact on supply chain management, maritime routes and the use of transshipment hubs.
Ashby, M.F. 2015. Materials and sustainable development, table A.14. Oxford: Butterworth-Heinemann.
FW. 2020. How many gallons of fuel does a container ship carry? freightwaves.com
Smil, V. 2013. Prime movers of globalization. The history and impact of diesel engines and gas turbines. Cambridge: The MIT press.
Stopford, M. 2010. How shipping has changed the world and the social impact of shipping. Global Maritime Environmental Congress.
Notteboom, T., et al. 2009. Fuel surcharge practices of container shipping lines: Is it about cost recovery or revenue making?. Proceedings of the 2009 International Association of Maritime Economists (IAME) Conference, June, Copenhagen, Denmark.
UNCTAD. 2012. Review of maritime transport. United Nations.