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  • Smarter steaming ahead

    Briefing on a report by CE Delft studying the impacts of vessel speed on emissions, technical constraints and other experiences with regard to slow steaming and current speed regulations. The briefing was re-printed in 2017 to meet fresh demand.



    International shipping accounts for around 3% of global CO2 emissions. Shipping emissions will grow as world trade grows and, together with aviation, are estimated to comprise 4% to 5.7% of global CO2 emissions in 2020 (UNEP) and some 10% to 32% in 2050 unless action is taken. The International Maritime Organisation (IMO) has been discussing what to do since it was tasked with reducing emissions from international shipping by the 1997 Kyoto Protocol. An IMO action plan on market-based measures is now in its 10th year.

    A good number of policy options ranging from emissions trading, a global carbon levy, to efficiency trading and mandatory emission reductions by ship have been proposed, debated, studied and amended during this time and remain under consideration. The Energy Efficiency Design Index (EEDI) for new ships and Ship Energy Efficiency Management Plan (SEEMP) for existing ships were agreed in 2011.At the IMO’s Marine Environment Protection Committee (MEPC 61) in September 2010, the IMO considered a proposal from the Clean Shipping Coalition (CSC) to apply speed restrictions to ships to reduce emissions, with CSC noting that average ship speeds have crept up over the past 20 years despite rising fuel costs and that fuel consumption and thus emissions are a cubic function of speed. However the IMO dismissed any further consideration of CSC’s proposal for regulating ship speed after only a very brief exchange of views. This subsequent study seeks to investigate further and underpin the legal, environmental and economic feasibility of regulated slow steaming i.e. slow steaming at or beyond the level that companies initiate themselves. 


    Slow steaming, first practiced in the 70s, is a relatively recent phenomenon, being widely adopted as a response to the slump in demand and oversupply of ships that accompanied the start of the current economic crisis. The practice has been further extended since 2008 and has brought widespread benefits to shipping companies who have now embraced it as a useful operational measure to lower fuel costs.

    Slow steaming has resulted in a significant reduction in emissions of GHGs and air pollution. However there is a widespread expectation in the industry that as the economy and markets pick up and excess capacity is brought back into service, speeds will increase again over time to meet the growing demand. If this occurs, we can expect a significant and sustained increase in ship emissions just at the time when long-term IMO initiatives to address shipping’s carbon footprint are hopefully reaching a conclusion. Capping speeds at or around their current crisis levels – which estimates suggest could be 10-15% below their 2007 maximum – would prevent this from happening and avoid a market speed up largely negating the effect of any long-fought-for climate measure the IMO might adopt.

    Speed restriction in the road and rail sectors is commonplace – mainly for safety but also for environmental reasons. Industry has however argued strongly that restricting speed in the shipping sector is not appropriate as it limits flexibility and will have negative safety, logistics and cost implications and result in a poor environmental outcome due to the need to build and operate additional ships.

    This brochure provides a quick overview of the findings of a study into the policy options, costs and benefits of regulated slow steaming commissioned by T&E and Seas at Risk. The authors were CE Delft, Professor  Mikis Tsimplis and The ICCT. The study effectively dismisses all the common concerns surrounding speed limitation as unfounded. Moreover it clearly demonstrates that regulated slow steaming not only reduces CO2 and other emissions dramatically, it actually saves the sector money. Implemented carefully – e.g. by including certain provisions for ships that need to travel faster – such an intelligent approach to regulated slow steaming would provide industry with the flexibility they say they need. Such a provision could also be constructed in a way that raised revenues which could be used for climate change purposes.

    When the Clean Shipping Coalition raised the issue of regulated slow steaming at the IMO in 2010, the idea was dismissed with very little discussion. Yet slow steaming has proven itself to be the only effective measure that has actually delivered significant in-sector emission reductions over past years. The industry may soon be on the verge of seeing average speeds increase again, potentially negating all those emissions reductions. The CE Delft study looks carefully at all the concerns about speed limitation. We believe it provides the necessary background to enable the IMO to revisit the issue. Time is of the essence.

    It is not our intention to suggest that regulated slow steaming is the silver bullet to address shipping’s climate impact. A range of efficiency and market-based initiatives is urgently needed. Our hope is to overcome the knee-jerk reactions which may have prevented this most simple and obvious of measures to reduce emissions from being given proper and detailed consideration.

    Regulated slow steaming can produce emissions reductions by 2030 and 2050 which rival any other reduction option being considered at IMO or EU level. And it can do so with a sizeable economic gain. If we are serious about tackling shipping GHG emissions and making sure that the shipping industry contributes its fair share to tackling climate change, then the IMO – and industry – must look again at regulated slow steaming and give it full and proper consideration.

    John Maggs, Seas At Risk
    Bill Hemmings, Transport & Environment
    Members of the Clean Shipping Coalition

    Highlights from the study

    • Slow steaming has significant multiple environmental benefits

    A 10% reduction in fleet average speed results in a 19% reduction of CO2 emissions even after accounting for the emissions of additional ships needed to deliver the same amount of transport work and the emissions associated with building the necessary additional ships. Emissions of SOx, NOx and probably black carbon will decrease in line with fuel use and CO2 emissions. A ship speed reduction of 25% leads to a reduction of main engine fuel consumption of approximately 58% on a ship year basis. Fuel savings on a fleet level will be somewhat less as explained in the report. Lower ship speeds will also reduce whale strikes and other harmful wildlife interactions.

    • Slow steaming has significant economic benefits

    Taking into account both the direct costs (fuel use, crew, capital costs of ships), indirect costs (additional inventory costs, adjustment of logistical chains) and the external costs (impacts of emissions on human health and ecosystems, climate impacts), the benefits of slow steaming outweigh the costs. This result is robust for a number of fuel price assumptions and discount rates. Implemented correctly, regulated slow steaming is cost free to the shipping industry as a whole and entails marginal incremental logistic and supply chain costs to consumers.

    • There are very few, if any, evident technical obstacles to slow steaming

    Many shipping companies have experience with slow steaming in recent years. Even at very low engine loads, they have encountered only a few problems and these problems could be surmounted by small changes to operational procedures. Hence, it appears that there are very few technical constraints to slow steaming.

    • Regulated slow steaming is legally feasible

    Compulsory slow steaming can be imposed by a State on the ships flying its flag; on all ships in territorial waters (but cant be enforced while the ship is on transit or innocent passage); and in the Exclusive Economic Zone (EEZ) and the high seas as a condition of port entry of the imposing States.

    • Regulated slow steaming is feasible to implement

    Regulated slow steaming is relatively easy to monitor and enforce, and may have a lower administrative burden than some of the recently proposed MBMs. Speed can be monitored, both by ships and by regulators, and reported to regulators with little additional effort. Enforcement can be based on existing port State control instruments.

    • Regulated slow steaming delivers emission cuts in-sector

    Regulated slow steaming ensures that emissions in the shipping sector will be reduced from business-as-usual levels, regardless of the fuel price and demand for shipping.

    • Regulated slow steaming could avert a ship emissions spike as the global economy picks up

    A cap on speed would reduce the possibility of an otherwise likely large and long-term spike in emissions if ships speed up in response to a recovery in demand. A cap set today around current average ship speeds will have little impact on industry.