“Effectively addressing climate change is possibly the greatest challenge of our time,” the letter states, noting that the IMO agreed in April 2018 on an initial greenhouse gas strategy that calls for shipping emissions to peak as soon as possible and reducing shipping’s “carbon intensity” by at least 40 percent by 2030 and for total emissions to be cut by at least 50 percent by 2050 compared to 2008 while aiming for full decarbonization.
The letter notes that after the 2008 economic crash, shipping companies reduced ship speeds and that led to dramatic reductions in greenhouse gas (GHG) emissions.
“This speaks to the real-world effectiveness of a potential prescriptive speed measure in helping achieve reduction targets. However, recent studies also suggest that ships are speeding up again as global demand recovers. Should this trend continue, any GHG gains from slow steaming over recent years will disappear.”
Slowing ships can dramatically reduce fuel consumption and costs, but it also can add costs for shippers in the form of higher inventory carrying costs and making ocean transportation less attractive for goods with limited shelf life, be they perishables such as fresh produce or meat or “fast fashion” apparel.
The letter was dominated by bulk shipping companies.
WSC added it "will continue to work with all parties through the IMO to create lasting solutions that will allow the industry to achieve the emissions reduction objectives that the IMO has set."
Anna Ziou, policy director of the U.K. Chamber of Shipping, said in an article in Lloyd's List and posted on the Chamber's website that "The idea of regulating speed limits to slow down ships to cut fuel consumption and carbon intensity of the industry is not new in the IMO; however, so far it has been politically unacceptable due to the direct impact that it might have to trade. "
"If the IMO decides to rely on prescriptive speed regulation to meet its short-term target, it would delay the low-carbon transition and store up greater costs later on for the industry," she argued.
Among the other issues she raised was the possibility that slower speeds might encourage shippers to use different modes of transportation resulting in "higher aggregate greenhouse gas emissions in the case of time-sensitive cargos, particularly in the short sea segment."
A 2010 article appearing Wartsila Technical Journal published by the engine manufacturer Wartsila, explained why slow steaming is so effective this way: "The biggest single cost factor in merchant shipping, particularly for container and other large vessels, is the fuel oil. And the easiest way to reduce this cost is to reduce the ship’s speed. The typical propulsion system for larger merchant ships is a low-speed two-stroke main engine, directly driving the fixed-pitch propeller via the propeller shaft. The ship’s speed is, therefore, reduced by lowering the speed of the engine and propeller. The power required from the main engine, however, correlates disproportionately with the ship’s speed."
"For example, reducing the nominal ship speed from 27 to 22 knots (-19 percent) will reduce the engine power to 42 percent of its nominal output (CMCR). This results in hourly main engine fuel oil savings of approximately 58 percent. A further reduction down to 18 knots saves already 75 percent of the fuel. The reduced speed however results in a longer voyage time; therefore the fuel savings per roundtrip (for example Asia-Europe-Asia) are reduced by 45 percent at 22 knots, or 59 percent at 18 knots. These are calculated values, and the actual values depend also on a number of external factors, such as the loaded cargo, vessel trim, weather conditions, and so."
Since weekly fixed day service (at least on schedules--the ability to keep to a schedule may be affected by factors such as weather and port congestion) has become the norm on major container routes, carriers may need to add additional ships to a string so they can continue to, for example, have a ship in an Asia-North Europe rotation show up in Rotterdam every Monday. So the capital cost or charter cost to a liner company may increase as a result of slow steaming if the carrier wants to continue to offer a fixed day schedule.