Repowering Is Likeliest Path To Lower Carbon On Waterways

Repowering the existing towboat fleet with greener, less carbon-intensive fuels is the most promising and cost-effective path toward reducing carbon emissions on the inland waterways.

That’s a key conclusion of a webinar discussing implications of a major study by Vanderbilt University that seeks to sketch out pathways to possible decarbonization for U.S. inland waterways stakeholders. The report, Decarbonization of the Inland Waterways Sector in the United States, was prepared for ABS. It claims to be “the first to examine the U.S. inland waterway system through the lens of reducing greenhouse gas emissions.”

The webinar was held September 27. Presenters included report co-authors Leah Dundon, director of the Vanderbilt [University] Climate Change Initiative; Sotirios Mamalis, global sustainability manager, fuels and technology at ABS; and David Sehrt, consultant and former chief engineering officer at Ingram Barge Company. The presenters covered what regulations or incentives could drive change within the market, the look and operation of an electrified river towboat and which alternative fuels would be best suited for the inland fleet.

Inland Paths To Lower Carbon

Several factors unique to the inland waterways, as opposed to the oceans, will drive the path toward lower carbon. In the webinar, Sehrt said new fuels offer the fastest path to decarbonization—but not without challenges. 

The inland waterways already are greener than competing forms of transportation, even with current fuels. While more could be and will be done, simply switching cargoes to the inland waterways (where possible) already gives shippers and companies a green bonus.

The U.S. inland waterways are not subject to the mandates of the International Marine Organization, whose Maritime Environment Protection Committee has approved a mandatory measure to require a 40 percent reduction in carbon intensity in the shipping industry by 2040, using 2008 as a baseline—with an additional goal of a 70 percent reduction by 2050.

Inland marine equipment turns over more slowly than equipment on the world’s oceans. A freshwater towboat can last 50 years or more, whereas ocean-going vessels have experienced more rapid turnover in recent years for many reasons, including the ups and downs of the shipping business; consolidation of shipping companies; the push for lower emissions; and the building of ever-larger container vessels to leverage cost efficiencies. Not too long ago, ocean-going vessels as young as five years old were being scrapped. 

Energy Density

Most of the fuels discussed for reducing carbon emissions, like liquefied natural gas, ammonia and hydrogen, have a lower energy density than diesel fuel. That means it takes a greater volume of liquid fuel to get an equivalent amount of energy. Sehrt displayed a chart showing that while biofuels can achieve up to 95 percent of the energy density of diesel, LNG has 54 percent, methanol and ammonia 39 percent and hydrogen only 23 percent. This translates into larger tank requirements. Some existing engines can burn methanol. 

The tanks need to be pressurized and also close to the vessel’s center of buoyancy. That, in turn, often requires either brand new vessels, or expensive vessel redesigns.


Electric batteries themselves emit zero carbon, although some is emitted during their manufacture. The decarbonization report’s research team found that electrifying larger river boats may not be feasible with current technology because of the large batteries required, raising issues similar to the larger tanks required for the low-emission fuels.  

However, “Battery power in smaller boats is technically feasible right now,” Sehrt said during the webinar. Each of the approximately 1,000 existing fleet boats uses about 100,000 gallons of marine diesel each year.

Retrofitting smaller fleet boats could be accomplished in the near-term, Sehrt said. Converting all fleet boats to electric propulsion could reduce total annual average industry diesel fuel consumption by approximately 20 percent, depending on the fuel types used to generate electricity. 

In addition, the draft and trim of the battery-powered boats would be “ideal and never change,” said Sehrt.

Renewable Diesel

One possibly promising fuel in terms of ease of use is renewable diesel.

According to the Alternate Fuels Data Center of the Department of Energy,  “Renewable diesel and biodiesel are not the same fuel.” Biodiesel is a mono-alkyl ester suitable for blending with petroleum diesel up to a 20 percent blendwall. 

Renewable diesel, on the other hand, is a hydrocarbon produced from various biomass materials, including soybean and other plant oils, through processes such as hydrotreating, gasification, pyrolysis and other technologies. It meets ASTM D975 specification for petroleum diesel—in other words, it performs exactly like some grades of diesel and is 100 percent substitutable for petroleum-based diesel. 

(Somewhat confusingly, other publications of the DOE use the term “biodiesel” when they mean renewable diesel.) According to the DOE, emissions reductions from renewable diesel can be substantial, including of CO2, NoX, and particulates. It is non-toxic and degrades into harmless organic ingredients. It can also use existing fuel facilities. 

The only drawback from an emissions standpoint is that its production is itself energy-intensive—and as society leans more toward carbon reduction, it is looking at the entire carbon footprint of a fuel. 

Customer Pressure

Some large corporations have made highly publicized efforts to look at the carbon intensity of their supply chains. Inland waterways companies are relatively small, and they need positive incentives to make costly investments. Dundon suggested in the webinar that grant opportunities for pilot projects to test low-carbon or zero-carbon alternatives would be a good incentive. 

A few inland carriers are public or are part of larger public companies. The Securities and Exchange Commission issued guidance in 2010 to assist public companies better understand how existing rules might require disclosure of climate change risks.

Dundon told The Waterways Journal that the SEC is considering passing either further guidance or, possibly, regulations governing the disclosure of climate risk. But even requiring reporting with no penalties attached can be an incentive, she said. “The reputational or brand effect could affect investors” and stockholders, she said. “Once a few companies are affected, the effects could ripple through an industry.”