U.S. naval architecture firm unveils design of LNG-fueled towboat

Ship Architects Inc. (SAI) of Daphne, Ala., has designed what is likely the first-ever towboat fueled by liquefied natural gas.

The long-haul line towboat would be 150 feet long and 50 feet wide with two 2,000-hp engines that are entirely powered by LNG, according to Joe Comer III, a naval architect with SAI.

Ship Architects decided to work on designs for LNG-fueled boats for the U.S. inland waterways as a response to stricter standards for diesel fuel emissions for the towing industry. Comer is part of a team that has worked on this design for over a year. The proposal would employ Rolls-Royce engines, but other engines could be used.

Some industry executives believe LNG will play a major role in vessel propulsion because of tighter emissions standards and the fact that LNG is cheaper than other marine fuels. By 2020 the majority of owners will be seeking ships powered by LNG, and LNG will become the dominant fuel for merchant ships, said Henrik O. Madsen, chief executive of the classification society Det Norske Veritas.

The proposed towboat would be 150 feet long and 50 feet wide and have four tanks each holding 30,000 gallons of LNG to fuel two 2,000-hp engines. The $2.2 million cost of the fuel tanks could be recouped in fuel savings in just a year and a half of operations, according to the boat’s designers. Courtesy Ship Architects Inc. (Photo courtesy Ship Architects, Inc.)

Worldwide there are several vessels either in service or being built using LNG for propulsion. The great majority are duel-fuel vessels that can switch between LNG and other marine fuels. These include oil platform supply vessels, coast guard vessels, passenger ferries, a high-speed ro-ro passenger ferry, a container vessel, LNG carriers and a very large crude carrier.

The Ship Architects’ LNG-powered towboat would save over $1.5 million annually compared with a similar towboat powered by a diesel engine, according to an SAI presentation at the 2010 International WorkBoat Show in New Orleans. This savings is based on each towboat taking 10 to 12 trips of 2,500 miles at 5 mph.

The proposed vessel requires four tanks, each holding 30,000 gallons of LNG, according to the SAI presentation. With the cost of the four tanks estimated at $2.2 million, they would be paid for in a year and a half. Ship Architects is close to an estimate of the total cost of the LNG-fueled towboat, but does not want to release that figure yet, said Gerald Moore, technical director at SAI.

Ship Architects is also working on designs for a truckable towboat and a fleeting pushboat, both using only LNG fuel, according to Moore.

Effective August 2012, an amendment to the International Convention for the Prevention of Pollution from Ships (MARPOL) establishes a fuel oil sulfur limit of 1 percent for ships operating within 200 miles of the coasts of the United States and Canada, according to the website of the federal Environmental Protection Agency. EPA Tier 4 regulations for marine diesel engines are even more stringent.

One way to meet these new standards could be the installation of more sophisticated scrubbers into current diesel engines. Another way could be the proposed LNG-towboat, according to Moore. The LNG-fueled engine eliminates 100 percent of sulfur emissions and particulates, according to the Ship Architects proposal, and 85 percent of the emissions of nitrogen oxides. Another advantage of LNG fuel is the price and availability.

“LNG is very plentiful,†said Moore. He noted that there is an abundant domestic supply of natural gas and that the price for LNG fuel is usually more predictable than for petroleum. “There is a probability that LNG prices will stay more stable than the price of petroleum products,†said Moore.

The major design challenge for the 150-foot LNG pushboat was to “make it look and touch and feel similar to an existing pushboat design and carry the required fuel,†said Comer. Finding a place for the LNG tanks was another challenge. Ship Architects solved that problem by locating the four tanks where the engine normally is and by putting the two 2,200-hp engines on the deck, near the vessel’s stern. The boat uses a z-drive propulsion system.

“The use of propulsion thrusters may be more controversial for the captains than the fuel type,†said Moore.

In addition, safety systems must be added to the vessel for the LNG fuel. If the tanks are enclosed, as they would be in the 150-foot, long-haul vessel, there need to be gas detectors, alarms and firefighting systems, said Moore. But for the truckable towboat, the LNG tanks could be on top of the vessel and not enclosed, simplifying safety issues.

Refueling for short-haul inland vessels could be done from tanker trucks, Moore said. Refueling for the long-haul vessel could be done from barges on shore or from barges brought to the vessel in midstream.

One problem with the LNG concept is that existing towboats likely cannot be retrofitted. “Converting the older boats may be a bit of a challenge because there is such a design change,†Comer said.

John Hatley, vice president of ship power for Wärtsilä North America, sees tremendous potential for this technology as it spreads from use on larger oceangoing vessels to use on inland waterway vessels.

“This is certainly exciting in that it might bring some revolutionary concepts to the inland rivers,†Hatley said.

Wärtsilä was one of the companies Ship Architects consulted regarding engines for the LNG-fueled long-haul line towboat. SAI also worked with Rolls-Royce, Trussville Utilities’ LNG gas division, Chart Ind., TGE Marine Gas Engineering, the American Bureau of Shipping and the U.S. Coast Guard, according to Comer.

David A. Tyler

By Professional Mariner Staff