Slow steaming is the practice of operating transoceanic cargo ships, especially container ships, at significantly less than their maximum speed. In 2010, an analyst at the National Ports and Waterways Institute stated that nearly all global shipping lines were using slow steaming to save money on fuel.
Rationale and history
Slow steaming was adopted in 2007 in the face of rapidly rising fuel oil costs, which was 700 USD per tonne between July 2007 to July 2008. According to Maersk Line, who introduced the practice in 2009 to 2010, slow steaming is conducted at 18 knots (33 km/h; 21 mph). Speeds of 14 to 16 kn (26 to 30 km/h; 16 to 18 mph) were used on Asia-Europe backhaul routes in 2010. Speeds under 18 kn (33 km/h; 21 mph) are called super slow steaming. Marine engine manufacturer Wärtsilä calculates that fuel consumption can be reduced by 59% by reducing cargo ship speed from 27 knots to 18 kn (33 km/h; 21 mph), at the cost of an additional week's sailing time on Asia-Europe routes. It adds a comparable 4 to 7 days to trans-Pacific voyages.
The container ship Emma Maersk can save 4,000 metric tons of fuel oil on a Europe-Singapore voyage by slow steaming. At a typical 2008 price of USD 600-700 per tonne, this works out to USD 2.4-2.8 million fuel savings on a typical one-way voyage. Maersk's Triple E class of ships was designed for slow steaming, with hulls optimized for lower speeds. Because of this, it has less powerful engines than its predecessors.
Cost and benefits
Lowering speed reduces fuel consumption because the force of drag imparted by a fluid increases quadratically with increase in speed. Thus traveling twice as fast requires four times as much energy and therefore fuel for a given distance. The power needed to overcome drag is the product of the force times speed and thus becomes the cube of the speed at high Reynolds numbers. This is why driving an automobile at 80 km/h (50 mph) requires less than 85% of the power required by the same automobile driving at 100 km/h (60 mph).
Although lowering speeds reduces the power requirements, the overall benefits of speed reduction may be limited by other factors, such as economically viable total voyage time, and the fact that a ship's engine and propeller are designed to operate within a certain RPM range. Steaming too slowly may place the engine and propeller outside their most efficient range, and will therefore begin to counteract the benefits. Also, there are fixed costs, such as crew wages and charter rates, that will increase if the voyage is longer. Although some ships are being put into service that are designed to steam most efficiently at slower speeds, the great cost of building a ship and need to remain competitive means that radical changes are unlikely until conditions merit such a risk.
The trade off between fuel cost savings against the increased costs of personnel, insurance and inventory due to the longer voyage duration is a significant logistical issue. Commercial vessels seek to adhere reliably to schedules; if a ship is planned to slow steam, it may normally speed up should it encounter en route delays (such as bad weather or deviation) so as to recover its original scheduled arrival time. The initiative to balance cost, duration, emissions and risk is supported by the EC-funded research project SYNCHRO-NET.
"Smart steaming" is a strategy by which the vessel speed is dynamically optimised based on the real-time state of the sea, weather and the destination port - for example if there is congestion at the port there is little point in rushing to get there at full speed simply to then wait for a berth for days - instead the ship can go more slowly to conserve fuel and still berth at the same time.
The International Maritime Organisation's GloMEEP project has also studied this subject, and refers to "Just in time Ship Operations".
Smart Steaming has the potential to deliver many benefits. For example the SYNCHRO-NET project has reported examples of up to 30% reduction in fuel usage for the ship, which, broadly speaking, means a similar reduction in cost and greenhouse gas emissions.
Technically and operationally smart steaming presents some challenges. Ship control systems have to be more sophisticated, and multi-objective optimization techniques are needed which can respond to changing conditions (e.g. weather, sea state, port status). Improvements in ship/port communications are also needed, as well as new commercial and legal agreements between relevant stakeholders: ship operator, ship owner, port/terminal operator and the customer/freight forwarder whose goods are being carried by the ship.
- Glossary of terms (PDF), Maersk, 31 October 2014, archived from the original (PDF) on 31 October 2014
- "Ocean shipping lines cut speed to save fuel costs", LA Times, July 31, 2010
- "No slower steaming as container lines run like clippers", Bloomberg Business, January 26, 2012
- Container Ship Focus] (PDF), Lloyd's Registry, September 2008, archived from the original (PDF) on 2012-05-26
- Slow steaming - the full story (PDF), Maersk, 2011, archived from the original (PDF) on 2012-11-02
- Presenna Nambiar (July 25, 2011), "'Slow steaming' slows down delivery of goods", New Straits Times, archived from the original on April 9, 2016 – via HighBeam Research
- "Carriers Move Full Speed into Slow Steaming", Journal of Commerce, January 12, 2010
- Slow steaming – a viable long-term option? (PDF), Wärtsilä
- Steamship Mutual report
- Slow steaming guide
- Note that if a variable pitch propeller is fitted, slow steaming may be accomplished effectively.
- The economics of slow steaming
- Is Slow Steaming Good for the Supply Chain?
- https://www.mjc2.com/synchronet.htm - SYNCHRO-NET: Smart Steaming and Synchro-modal Logistics.
- https://glomeep.imo.org/ - GloMEEP - Just-in-time ship Operations.
- https://www.mjc2.com/synchro-net-smart-steaming-supply-chain.htm - Smart Steaming and De-stressing the Supply Chain.