Vessel Profile: It Takes a Village to Build a Hybrid-Electric Ferry

Seattle’s Elliott Bay Design Group shapes a new hybrid-electric, double-ended ferry for Casco Bay Lines of Maine.

The 164-foot, double-ended hybrid-electric ferry Machigonne II, as conceived by Elliott Bay Design Group. Image: EBDG.

A 164-foot, double-ended hybrid-electric ferry from Seattle-based Elliott Bay Design Group (EBDG) was chosen by Casco Bay Lines (CBL) of Portland, Maine, to enter the construction phase at Senesco Marine of North Kingston, R.I., this fall.

The new ferry is expected to enter service in 2024 to replace the existing Machigonne II diesel-powered ferry that operates between Portland and Peaks Island, Maine. Crowley Maritime announced in August that they were selected by Senesco Marine to provide design verification and production packaging for the project.

“Casco Bay is a new client for us,” said Matthew Williamson, a senior project manager at Elliott Bay. He joined the firm in 2006 and has an extensive ferry design portfolio from coast to coast and Alaska to the south. “It’s the first time we’ve worked with them on this project, and they have been absolutely fabulous to work with. Very engaged, very curious. Just what we like in a client, somebody who is paying attention.”

Elliott Bay Technical Director Lydia Benger said the group has finished the design phase.

“Contract design doesn’t give you all the nuts and bolts to build the boat, but it provides the basic parameters,” she said. “Now Crowley and Senesco will complete the detailed design and start construction for the boat. It’s all within the 24-month timeline to complete the construction.”

Williamson described the project status as “just in the infancy of the construction contract at this point.”

Inception to Conception

According to Williamson, the new hybrid-electric ferry came about due to a CBL RFP released in 2017 for a replacement for the Machigonne II. The RFP was not specifically for a double-ended, hybrid-electric ferry, but it prioritized the best design upgrade for the operating route.

“It [the Machigonne II] is CBL’s only vehicle ferry, aside from some crane-lift, single-car options to some of the other islands,” said Benger. The project began official work in 2018. According to Benger, Elliott Bay conducted several studies with CBL to home in on desirable design attributes for the Maine operator.

“Part of our design spiral was specifications-based questions like, how big is the boat? How many ends does the boat have?” Benger said. The new ferry will have capacity for 15 vehicles and 599 passengers across three decks that include an open sundeck. The propulsion selection study started with the baseline of a traditional mechanical direct-drive diesel engine.

“As that process evolved, I think both Casco Bay and EBDG thought, you know, battery technology is maturing and this could be an opportunity,” Benger remarked.

Double-Ended Design, Hybrid-Electric Propulsion

While double-ended ferries are common on Puget Sound, Wash., where Elliott Bay is based, CBL does not currently have a such a ferry in service. As the firm’s studies progressed, a major benefit of a double-ended design turned out to be sustainability.

“We looked at a double-ended ferry versus single-ended ferry,” Williamson said. “With the reduced travel time afforded by not having to turn the vessel around, we could go slower with a double-ended design. Going slower requires less power, so that was an advantage for us as we started to consider the battery hybrid options.”

The current operating route between Portland and Peaks Island is a 2.2-nautical mile crossing. CBL makes round trips once an hour. The double-ended design coupled with the relatively short and regular route gave the hybrid-electric propulsion concept a pragmatic boost. Ultimately an ABB Marine & Ports (ABB) hybrid propulsion system that supports both diesel-electric and zero-emissions battery-powered modes was selected.

Elliott Bay has said that the new ferry will result in an emissions reduction of 800 tons of carbon dioxide per year. If the EPA figure that the typical passenger vehicle emits about five tons of carbon dioxide a year is used, this means upgrading the Machigonne II to the new ferry is roughly equivalent to removing 160 cars off the road. Add the noise reduction potential, and the environmental impact case for the new ferry appears substantial.

Is hybrid-electric propulsion the new standard for ferries?

“We’ve done quite a few electrification and hybrid studies for various clients over the last couple of years,” Benger remarked. “It varies for every operator. Everyone runs a different route. It’s not like you can just run a bunch of Teslas off the line and have them all work for every ferry operator. The routes are different. The carrier is different.”

She cited the shoreside infrastructure as a big factor for CBL. Shoreside power infrastructure in Portland is available. After modifications to the ferry terminal, charging should be routine.

“It should be a relatively simple modification to bring power to the vessel,” said Benger, who also explained that there’s not an opportunity to charge the vessel at Peaks Island due to lack of infrastructure and available power.

“Every client is different. Every route is different,” she remarked. “It works very well for Casco Bay because they have power available [in Portland].”

When asked about the viability of other alternative fuels like hydrogen or methanol for this project, Williamson said nothing was eliminated right off the bat, but feasibility obstacles abounded for this project.

“One of the things about some of these alternative fuels other than electricity is the availability of them,” he said. “Kind of the last mile if you will … those alternative fuels just wouldn’t have penciled out for Casco Bay to adopt them.”

Williamson also pointed out that while many of these new alternative fuels are in their infancy, hybrid-electric technology is not new.

“Hybrid-electric systems have been in service in Europe for many years, it’s just new to the United States,” he explained. “It’s not hard to make a reliable system, whereas some of the alternative fuel technologies are relatively new. It’s not typically the place of a public ferry operator to take that risk on, the brand-new technology on the bleeding edge.”

Hybrid-Electric Ferry Treads, Considerations

“I think we’re going to see a lot more hybrid innovations where the appropriate application makes sense,” Benger predicted. “I think it always needs to be verified that it’s right. Sometimes all-electric is not the answer and a hybrid can offer you savings. We have instances too where adding batteries is less efficient and is not the right answer. As much as the desire is to be greener, sometimes the green answer is to be diesel. That’s something we need to check every time.”

According to Williamson, Elliott Bay has four electric-hybrid designs that have either been awarded for construction or are about to be, including the CBL ferry.

“I think it’s very much on the forefront of ferry operators’ minds to look in this direction,” he stated. “It’s not necessarily the least expensive way to procure a ferry from the cost-capital standpoint, but sometimes when looking at trends, those first costs aren’t as important as being mindful of our environment and respectful of the operations. I think the trend is definitely heading toward battery hybrid or all-electric propulsion.”

He said he’s hopeful that with time, acceptance, and market penetration that the prices will become more affordable.

Major factors for hybrid-electric or all-electric adoptions for public transit ferries are shoreside power infrastructure and relationships with electricity providers.

“It comes down to the operators’ negotiated rate with their electricity provider,” Benger said. “Basically, electricity is provided at speed and demand.”

Speed and demand refer to when a ferry operator needs power and how much. These variables effect the price per kilowatt. Quickly topping off a ferry’s batteries can be much more expensive during high energy demand hours. Different operators on land and sea, such as New York City’s subway system, have unique agreements with an area’s electricity provider to offset this.

“There are smart ways to overcome those instant demand charges,” Williamson said. One such method is to maintain large power storage capabilities on-site at the ferry terminal. These super shoreside battery banks can be charged at low demand hours for cheaper electricity while a ferry can charge from them whenever operations demand.

“It’s like the battery you carry around to plug your cell phone into when you’re out of juice,” Williamson chuckled. “Batteries to charge batteries.”

Next Steps

At the time of this writing, CBL is going through significant ferry terminal modifications to prepare for the anticipated 2024 arrival of the new ferry. German mechanical engineering company Stemmann Technik’s rapid FerryCHARGER shore-charging system, to be provided by ABB, was announced in July.

“We have some design and construction oversight while we continue to support our client during construction,” Benger said. “We have continuing touch points on the project over the next 24 months.”

Overall, Benger said Elliott Bay has a sense of accomplishment about the project.

“It feels good,” she remarked. “It’s exciting every time one of our clients is entering the construction phase. I’m ready to see it work.”  

Norris Comer is a Seattle-based writer and author. His debut memoir, Salmon in the Seine: Alaskan Memories of Life, Death, & Everything In-Between is now available wherever books are sold. You can find him on Substack, Instagram and at