First US plug-in hybrid inland towing tug delivered

The vessel will be owned by Kirby Inland Marine, LP, a subsidiary of Houston-based Kirby Corporation, and has been time chartered by Shell Trading (US) Company, which will use the boat to push barges throughout the Houston port region.

The Green Diamond was constructed by San Jac Marine, LLC, Kirby’s shipyard in Channelview, Texas. The power management, control and propulsion systems were supplied by Stewart & Stevenson Manufacturing Technologies.

The 1,243kWh energy storage system was supplied by Corvus Energy. Corvus noted that the Corvus Orca ESS featured its patented passive single-cell thermal isolation and proven forced-air cooling to deliver the highest standards of safety and performance.

The hybrid propulsion system consists of two 575 KW Danfoss electric motors that can be driven either by the Corvus Orca series battery system, or, if needed, onboard Caterpillar generators.

A Zinus charging system purchased from Zinus will be used for dockside charging of the battery system, allowing the vessel to operate on trips within the Houston area without ever needing to start the generators. When no shore charging is available, the hybrid towboat will have an estimated 27% reduction in fuel used and CO2 emissions.

With shore charging, fuel use will be reduced by almost 80%, resulting in an 88%-95% reduction in emissions of NOx, CO, and HC. Engine run time is estimated to be reduced between 93%-98% compared with a conventional inland towing vessel, resulting in significantly decreased maintenance costs.

“The plug-in hybrid design offers numerous advantages for towboats in certain trades,” said Mitch Jones, Vice President of San Jac Marine. “We are already looking at building follow-on vessels.”

Ole Jacob Irgens, Corvus Energy – Executive Vice President commented “Inland and harbor tugs are ideal candidates for electrification with batteries because their routes are shorter, in proximity to the shore, and have limited power demands. We’re seeing significant interest from tug owner/operators, designers, and builders right now.”