LNG Powered Towboat Design Receives Approval in Principle

Illustration courtesy The Shearer Group
Illustration courtesy The Shearer Group

The push for liquified natural gas as a marine fuel across a multitude of vessel types continues with the “Approval in Principle” of an LNG-powered inland towboat for the domestic U.S. market.

The design for the 4,200 horsepower LNG towboat was developed by Louisiana-based Conrad Shipyard and the naval architecture firm The Shearer Group, Inc. (TSGI), with the “Approval in Principle” being awarded by the American Bureau of Shipping.

The towboat is based on TSGI’s proven azimuth drive (z-drive) towboat design that debuted in 2008 with the “FRANK T. STEGBAUER”. To date, eight such towboats, including both 3,200 bhp and 2,400 bhp versions, have been built for Southern Towing Company and have helped pioneer the use of z-drives for brown water operations and shown significant fuel savings relative to conventional towboats.

The new LNG powered towboat design incorporates Wärtsilä’s dual fuel technology that is already widely accepted, but TSGI notes that the towboat design is not wedded to it. While Wärtsilä’s existing dual fuel engines are medium speed diesels, it is anticipated that future engine developments will result in lighter and smaller high speed units, with the design of the LNG towboat flexible enough to allow for the use of either engine option as determined by the operator.

“By combining two widely accepted technologies; z-drives and Wärtsilä’s dual fuel engines and fuel system, we have mitigated most of the risks associated with being an early adopter of this novel technology” says Greg Beers, P.E., TSGI’s President. “By incorporating proven technologies, we have minimized the risks that first movers will be taking with the switch to utilizing LNG as a fuel.”

According to TSGI, the Wärtsilä system specified in the design of the towboat is basically a smaller version of the system currently being used in the construction of Harvey Gulf International’s dual fuel offshore support vessels.

Building on this, TSGI says that the dual fuel technology coupled with the z-drive technology can lead to operational cost savings that can exceed 35% compared to a conventional towboat.

TSGI and its sister company, Bristol Harbor Group, Inc., have been involved in LNG projects since 2009, and are currently involved in five active LNG projects, including one for the United States Army Corps of Engineers.