One Year In, Green Diamond Performing Well

Kirby Inland Marine (Kirby) christened the mv. Green Diamond, said to be the nation’s first hybrid-electric towboat, on August 25, 2023, in a festive ceremony at the company’s Old River Fleet in Channelview, Texas. Now, with about a year of operation in the books for the first-of-its-kind vessel, Kirby leaders report the Green Diamond is performing well and exceeding expectations.

The 74- by 30-foot mv. Green Diamond is a plug-in hybrid-electric towing vessel, which means, rather than a pair of main engines, it’s equipped with a pair of battery rooms that house Orca energy storage systems sourced from Corvus Energy. Those two battery arrays drive the Green Diamond’s two 575 kW electric motors sourced from Danfoss. The electric motors, which combine for the equivalent of 1,800 hp., are then mated to Reintjes gears, supplied by Karl Senner. Together, they turn 72- by 51-inch stainless steel propellers. Kirby installed a charging station that allows the boat to power up with certified green electricity.

When battery power is exhausted, Green Diamond’s two Caterpillar C18 generators switch on, both driving the propulsion system and charging the batteries. As soon as the batteries are sufficiently charged, the generators switch off, and the vessel returns to all-electric operation.

David Hanson, vice president of product innovation for Stewart & Stevenson Manufacturing Technologies, which Kirby acquired in 2017, said the Kirby team definitely put in the time and effort to research and design what eventually became the Green Diamond.

“When we designed this boat originally, we sold it internally by developing a simulator and showing that we could get a dramatic reduction in fuel consumption and emissions,” Hanson said. “We were able to get the boat approved, and so far, the actual operational data coming in has far exceeded our modeling. A lot of the assumptions we used in the simulator were conservative assumptions. The boat has just absolutely exceeded our expectations in terms of fuel consumption and emissions. It’s been really, really eye-opening.”

In terms of efficiency, the Kirby team focuses on the percentage of uptime when the Green Diamond is operating on battery power only.

“Right now, that’s significant,” Hanson said. “It’s spending almost two-thirds of its time just on battery. Another big chunk of its time is on shore power, so the generators are really running less than 10 percent of the time.”

When in battery mode, the Green Diamond is “silent, quiet, with no emissions,” Hanson said.

“She has spent most of her time within Houston in the ship channel, running from various fleets to various docks,” Hanson said. “On any given day, she may take a pair of empties to a particular dock and idle while the barges are loaded or discharged. During most of that time, the crew is living aboard, managing day to day tasks, and everything takes place on battery power. When they’re ready to go and take their load, quite often, they’ll start using quite a bit of power to accelerate, and the generators typically kick on. During this time, the batteries charge back up while they’re underway.”

When batteries are fully charged, the generators are designed to automatically kick off, with the Green Diamond seamlessly switching back to battery power.

“So it operates very much like a conventional boat,” Hanson said.

Ben Parrish, project manager for Kirby Corporation, said sticking close to the Houston Ship Channel has been a function of customer need and not a limitation of the boat itself.

“When David and his team, along with the shipyard, were designing the boat, the intent was that it would have a similar endurance of a conventional vessel,” Parrish said. “If it’s needed to take barges east to New Orleans tomorrow, it can do so.”

The Green Diamond has tankage for 6,500 gallons of fuel, which is a bit smaller than a similarly sized conventional towboat. Still, with the batteries, that’s an ample amount of fuel.

“The fuel tanks on there hold enough to keep her going for several months,” Hanson said.

With the Green Diamond’s innovations and leading-edge technology, crew members, including the vessel’s engineer, received some training beyond what’s typically seen on a traditional towboat. That started very early on in the build process.

“The engineer as well as the crew were involved in the outfitting at the shipyard,” said Andrew Willoughby, operations manager for Kirby. “Toward the end of the shipyard period, they were there being trained by David and his team, as well as by other vendors that were installing equipment. They understand the battery system. They know how to monitor it. They monitor it every day, and they know what to look for.”

Shoreside, the Kirby team monitors not only the function of the boat but also its performance, even making updates to its operational profile to improve performance.

 “We’ve been able to tune and configure and improve the system, learn all the nuances, the ins and outs, and make it as efficient as possible,” Hanson said.

From a long-term maintenance perspective, the vessel has the advantage of “fewer moving parts” than a conventional towboat, Hanson said. That, plus the low hours on the generators should make the Green Diamond less intense from a service and maintenance perspective.

“The vessel has just exceeded expectations in its performance,” Parrish said. “San Jac Marine did a tremendous job in the construction. Stewart & Stevenson Manufacturing Technologies, along with David’s group, designed all the algorithms and programming in house, and the collaboration within the company was terrific. We had high expectations for the boat, and I think it exceeded those. It really has done quite well.”

“There was a lot of preparation with this boat, multiple departments within the company and multiple companies working together,” Willoughby added. “From crafting the operating procedures to training the crew, there was a lot of time and effort put into preparations before we even put the boat into service. I think that’s why things are going well right now.”

Could the Green Diamond offer a glimpse of what the future might look like on the inland waterways? Parrish said “there’s still an infrastructure piece” with regard to installing shore chargers across the system. He compared that to the effort to deploy electric vehicle charging stations around the country.

“We’ve got to build out this infrastructure, and that requires significant partnerships across industry and at all levels of government, local, state and federal, to bring that about,” Parrish said.

Still, the Green Diamond gets attention wherever it’s working, Parrish said.

“It’s a shining example of what the future can look like,” he said.