Green Diamond | Kirby Inland Marine, Channelview, Texas
Kirby Inland Marine set a new standard for clean propulsion on the inland waterways with the arrival of Green Diamond, the first plug-in hybrid towboat operating in the United States.
The 73.5-foot “eco tug” features a hybrid propulsion system with Corvus Energy lithium-ion batteries, Caterpillar C18 generators, Danfoss electric motors and specialized Reintjes gears. At full charge, the batteries hold 1,243 kilowatt-hours of electricity, enough to push two loaded tank barges along the Houston Ship Channel for extended periods. Total output from the propulsion system exceeds 1,600 hp.
Charging occurs dockside using a system purchased by Shell New Energies, which partnered on the project. The charging system fully replenishes Green Diamond’s batteries within six hours.
Blake Beall, general manager of operations for Kirby Inland Marine, spoke at length about Green Diamond’s environmental benefits and quieter operating profile. But it’s still a workboat, he added, and it had to perform just like its conventionally driven counterparts.
“Making a boat that is environmentally friendly is one of the goals, but the main goal is to move cargo and move it safely,” Beall said in April aboard Green Diamond in Channelview, Texas. “Whenever the captain or wheelman asks for a command, the vessel needs to respond just like a conventional tug. When he asks for the power, it needs to be there.
“It is performing as we would expect and we are seeing a real difference in efficiency,” he continued.
Kirby Corp., the parent company of Kirby Inland Marine, operates the largest fleet of inland and offshore tank barges in the United States. Its vessels operate within the Mississippi River system, the Gulf Intracoastal Waterway and along the Atlantic and Pacific coasts. The company is based in Houston, the epicenter of the booming U.S. oil and gas industry, and its vessels maintain a large presence within the Houston Ship Channel.
Green Diamond operates from Kirby Inland Marine’s fleeting facility in Channelview. It primarily performs harbor work along Buffalo Bayou and the many fleeting areas on the San Jacinto River. Beall said it can work anywhere along the 52-mile Houston Ship Channel, which runs from Galveston to the Port of Houston facilities east of the city’s downtown.
Kirby’s plans for an “eco tug” came together almost four years ago. Multiple companies within the Kirby umbrella had a role in its development. San Jac Marine designed and built the tug at its Channelview shipyard. Stewart & Stevenson designed the hybrid propulsion and electrical integration system using decades of experience in the transportation and oil and gas industries.
Taken together, the vessel gives each project partner a real-world understanding of electric propulsion within a maritime industry that has begun embracing decarbonization. Those lessons will be applied to new electrification projects down the road.
“This is truly a vision to revolutionize what we can do with an inland towboat,” Christian O’Neil, president of Kirby Inland Marine and Kirby Offshore Marine, said during the vessel christening in August 2023. “We have put together the most efficient and high-performing inland vessel built in generations.”
Shell is a major partner in the project, and Shell Trading has time-chartered Green Diamond. Karrie Trauth, Shell’s senior vice president and head of shipping and maritime, said Green Diamond shows ambitious clean energy projects are possible within the inland transportation system.
“Green Diamond is really the first of its kind,” she said. “It gives the world a proof point, and it gives us here in the inland industry a proof point that you actually can decarbonize the North American and Jones Act towboat industry.”
Beall described Green Diamond’s power management system as the “brains” of the tug’s propulsion system. It constantly monitors power supplies and power demands to keep the vessel running optimally. In typical operations, Green Diamond will run on battery power. As those batteries are depleted, however, the system can activate one or both generators to provide electrical current for the Danfoss motors.
The Cat generators can each produce 575 kW of power, which can charge the Corvus lithium-ion batteries, supply power to the electric motors or perform both simultaneously while underway, Beall said.
The climate-controlled battery compartments are located forward on the main deck. The port and starboard battery rooms each contain five Corvus battery packs comprised of 22 modules per pack. Each module has 22 lithium-ion cells. Those 4,840 individual batteries feed power into an internal electric grid that sends it where it’s needed in real time.
Each battery room is equipped with a traditional CO2 fixed fire suppression system and a water mist cooling system that targets battery fires. Sensors in these spaces can recognize potentially dangerous gases and remove them through ventilation stacks rising off the second deck.
Shell Energy Solutions supplied the shoreside charging system. A single crewmember can handle the charging cable and plug it into a port inside the starboard push knee. Shell Energy Solutions acquires renewable energy credits to offset Green Diamond’s electrical usage, according to Kirby.
Based on its operating profile, Kirby expects Green Diamond will use 80 percent less fuel than a conventional diesel pushboat. Green Diamond’s carbon monoxide, hydrocarbons and nitrous oxide emissions will drop by up to 95 percent. Even with the two gensets running, the vessel will produce 27 percent lower emissions. Reduced engine utilization will extend periods between overhauls and cut maintenance costs.
Green Diamond is outfitted much like a traditional inland pushboat. The engine room located below deck features the Cat C18 gensets forward. An electricity filter “cleans” the power before it enters the Danfoss motors. Each motor is paired directly to Reintjes gearboxes that turn the steel shaft and ultimately the 72-inch, four-blade Sound propeller.
The crew galley and mess are located on the main deck, while the four crew cabins are located on the second deck with two on each side, separated by a head. The typical crew contingent is five people: a captain, pilot, chief engineer and two tankermen.
Sound and vibration are constants for crew used to spending any time on workboats. Green Diamond is quieter than a comparable diesel towboat due to the smaller engines below deck. But when running on battery power, the vessel is virtually silent.
“It’s very quiet up here,” Capt. Billy Patterson said of the spacious wheelhouse. “We’ve had people on board and we started moving and they didn’t even know we were off the dock.”
The wheelhouse is equipped with Furuno radar and navigation electronics. Displays on either side of the helm chair track battery performance, temperatures, charge levels and myriad other data points. A separate display mounted on the port side of the wheelhouse monitors the hybrid propulsion system. A smaller gauge above the operator’s sight line tracks battery charge levels and usage.
As for driving with electric propulsion, Patterson said it was a short learning curve. “It’s pretty intuitive,” he said. “But it is a little different because you have instant torque. There is no delay.”
The inland towing industry has long emphasized the environmental benefits of moving cargo by barge, which is substantially cleaner than using semitrailer trucks. Green Diamond takes those benefits even further.
Kirby Inland Marine has already gathered important lessons from Green Diamond and its performance. The company will apply those lessons into future hybrid-electric towboats that could operate longer distances under battery power, including routes from Houston to New Orleans or Corpus Christi, Texas.
“We are excited about this boat,” said Taylor Dickerson, vice president of project management for Kirby Marine Transportation, “and we are excited about the next one.” •