Harnessing Wind, Slower Speeds, Efficient Routing to Reduce Climate Impact

Discussions underway at the International Maritime Organization (IMO) on how to decarbonize shipping ignore effective near-term solutions including slow steaming, more efficient routing and wind-assist retrofits. 

The implementation of these advances could be achieved by strengthening the Carbon Intensity Indicator (CII), the IMO’s energy efficiency measure that has received little attention.  

The IMO’s Intersessional Working Group on Air Pollution and Energy Efficiency will meet to revise and improve the functioning of the CII in April. It will make recommendations to the Marine Environment Protection Committee before April 7. 

Most of the attention is focused on so-called mid-term measures: an economic element and a marine fuel standard, rather than on strengthening the CII. 

Incorporation of so-called short-term solutions will ensure better results for whatever mid-term measures are ultimately adopted. By incorporating wind-assist technologies, slow steaming, and more efficient routing, among others, ships will burn less dirty fuel and reduce emissions of greenhouse gases (GHGs), black carbon and other pollutants, resulting in healthier air and oceans. Slow steaming also will reduce underwater noise pollution and whale strikes. 

The CII is a mechanism that rates the energy efficiency of ship operations but provides minimal penalties for those that consistently rank below average. Instead, the measure should incentivize ship owners to improve operational efficiency, enabling shipping customers to recognize the carbon intensity of their shipping supply chain and select better rated ships. Unfortunately, weak enforcement undermines the effectiveness of this provision.   

Readily available wind technologies could reduce fuel costs as much as 30 percent, yet initial costs and operational concerns appear to be major reasons for industry resistance. 

Shipping companies that prioritize speed and flexibility may resist adoption of slow steaming and wind assist technologies. Although slow steaming can increase voyage times, fuel demands — which make up a large portion of total costs — decrease dramatically with slower speed. Faster speed will not achieve “just in time arrival” if a ship ends up sitting outside a port waiting for a berth.  

Wind-assist technologies, like rigid sails and rotors, require significant upfront investment for retrofitting existing vessels or integrating them into new ship designs. The effectiveness of wind-assist technologies depends on variable weather conditions, complicating planning and operations. However, wind propulsion would be a real game changer to avoid burning heavier residual fuels or expensive transition fuels. 

While there is growing interest and early industry adopters are experimenting with these technologies, broad implementation could be accelerated by resolving technical and regulatory barriers.

A 2023 white paper by the International Council on Clean Transportation (ICCT) concluded that wind-assisted propulsion — including rigid wing sails and rotor sails — offers significant annual fuel cost savings.  

ICCT concluded that: ‘Rotor sails are variable in performance based on route, heading, speed, and season, while wing sails consistently generate net positive energy.’ 

The initial investment to retrofit existing vessels with wind assist technologies can vary significantly depending on technology and vessel design, the ICCT study found. The cost of installing rotor sails can be more than a million dollars per unit, where the installation might be two or more units. Studies suggest that rotor sails can achieve fuel savings between 5 percent to 20 percent, depending on factors like wind conditions, routes and vessel speed. 

The initial investment to install rigid wing sails can range from a few hundred thousand to several million dollars, depending on the size and material of the sails. Fuel savings are estimated to be between 10 percent to 30 percent. 

However, the long-term fuel savings can be significant, potentially offsetting the initial investment over three to seven years — which can also fluctuate depending on fuel prices. For example, if a shipping company's fuel savings reach even the lower range of 10 percent to 20 percent, this can result in substantial cost reductions as fuel expenses typically are a major portion of operational costs. Combined with the environmental benefits, wind-assist is an increasingly attractive option for many shipping companies to meet decarbonization goals. 

The integration of these strategies — wind-assist, slow steaming, and routing efficiency — offers a multifaceted approach to improving maritime operations while adhering to emerging regulatory and market demands for sustainability. 

Shipping contributes significantly to global greenhouse gas emissions and climate change, primarily through the combustion of fossil fuels that power ships. The IMO, in its 2023 revised GHG Strategy, established new absolute emission reduction targets of 20 percent striving for 30 percent by 2030, 70 percent striving for 80 percent by 2040 and net zero by 2050.  

Achieving these goals requires more rapid incorporation of slow steaming, wind-assist technologies and routing efficiency throughout the shipping industry. Strengthening revisions to the CII should be adopted at upcoming IMO meetings to create more energy efficient ships, reduce demand for fuel, cut GHG emissions, and help meet near and long-term targets. A strong enforceable CII would be a powerful tool to minimize decarbonization costs, deliver benefits for ocean health, drive uptake of slower speeds, wind propulsion and operational efficiency approaches to ensure the GHG emissions from shipping peak and reduce immediately.  

 

About the Author:

Kay Brown is the Arctic Policy Director at Pacific Environment. Brown has broad experience in political, non-profit and public arenas, including 10 years of service as an Alaska State Representative.