VESSEL REVIEW | Harbor Charger – Hybrid ferry to serve New York City's Governors Island

New York City-based non-profit the Trust for Governors Island (TGI) recently welcomed a new hybrid diesel-electric Ro-Pax ferry to its fleet of vessels.

TGI said that the US$33 mil­lion Harbor Charger is the first hybrid-elec­tric pub­lic fer­ry in New York State and has the abil­i­ty to trav­el at speeds up to 66 per cent faster than cur­rent fer­ries.

The 180- by 62-foot (54- by 19-metre), battery-equipped Harbor Charger, which will replace TGI's 1956-built diesel-powered ferry Lt. Samuel S. Coursen, will be used to transport both residents and tourists to and from Governors Island in Manhattan. Charging infrastructure has also been put up at various points to support the ferry's daily operations.

The ferry was designed by the Elliott Bay Design Group (EBDG) of Seattle and built by Conrad Shipyard in Louisiana. It can transport up to 600 passengers plus 30 vehicles – or 1,200 people in passenger-only configuration – at cruising speed of between 10 and 12 knots.

“Harbor Charger is what we refer to as a ‘super-K’ vessel,” David Turner, Project Manager at EBDG, told Baird Maritime. “Subchapter K of 46 CFR defines the USCG requirements for small passenger vessels (i.e., vessels under 100 GRT) which, in this case, carry more than 150 passengers.

“We typically think of Subchapter K as being restricted to vessels carrying not more than 600 passengers, but it actually isn’t. When more than 600 passengers are carried certain requirements for large passenger vessels begin to apply and at least in my experience, such super-K vessels are rare.”

The ferry’s primary route is between the Battery Maritime Building in Manhattan and Soissons Landing on Governors Island. On this route, she will maintain a 30-minute tempo with services supplemented by another EBDG design, Governors 1.

“The vessel also had to be compatible with Yankee Pier on Governors Island as an alternate moorage location,” added Sam Waterhouse, Naval Architect/Technical Manager at EBDG. “During design, there was considerable discussion around alternate future routes and to some extent, flexibility was built into the design to support these considerations. For instance, we looked at the potential for side-loading.”

Versatile propulsion setup for various navigation modes

The vessel is configured as a hybrid diesel-electric, double-ended ferry with Schottel SRP 210 azimuthing thrusters, each driven by a 560kW motor. There are two Caterpillar C18 engines coupled with 595kW generators and two battery rooms, each housing 396 kWh of Siemens BlueVault batteries.

The ferry has three basic operating modes: diesel for long transits or when the vessel needs to be operated without the batteries online; hybrid, which is also the standard operating mode involving the combined employment of generators and batteries to optimise energy usage; and electric, wherein the vessel will operate purely on batteries.

Electric will be the primary operating mode once high-capacity shore charging infrastructure is available on Governors Island.

“The vessel would connect with a charger each time it docks at Soissons Landing, bringing the batteries to near full charge with more than sufficient energy for another round trip,” said Turner. “The generators will stay onboard as a backup power source only. With two separate battery rooms, a failure in one will not interrupt the vessel’s electrical grid.

“Exactly how the vessel operates will be determined over time, but one notion was that a single generator would run at optimal loading with the batteries being used for peak shaving. Keeping the generator at optimal loading can significantly reduce vessel emissions and fuel consumption.”

The Battery Maritime Building and Soissons Landing terminals served by the ferry have very specific infrastructure with which the vessel must interface, including with consideration given to future sea level rise.

“The terminals dictated the shape of the ends of the vessel and an extensive study was conducted to try and optimise the vessel freeboard to minimise high or low water challenges,” Waterhouse told Baird Maritime.

“From our perspective, the engine room configuration was certainly one of the biggest challenges [during construction]. EBDG provided a high level, notional layout of machinery during contract design but Conrad did an incredible job of making it all come together.”

Addressing space constraint issues

“There were moments during construction when it felt like the engine room was destined to live up to the old adage of stuffing everything into a five-gallon bucket, but in the end, there’s enough room you might just fit a ping pong table," added Turner. "While a few tight spaces remain and there are still spots where you’ll need to duck under ducting, overall, it all came together exceptionally well.”

Cabling, both in the engine room and elsewhere, also presented a challenge during construction for EBDG. More than 50,000 pounds (23,000 kg) of cables are routed throughout the vessel, and the builder was able to install everything properly.

“Every project brings lessons learned, and new designs often bring even more,” said Waterhouse. “Most of our projects involve a single hull, and I have not been involved in any with more than four, which means each vessel essentially functions as a prototype. In this case, both Conrad and the Trust for Governors Island provided valuable feedback on portions of the technical specification, and we plan to incorporate that into future projects.”

“Our internal approach to using the contractor's 3D model during construction oversight also evolved,” Turner told Baird Maritime. “This effort really emphasised the importance of conducting regular design model reviews and ensuring those efforts are properly budgeted.

“Switching to full electric capacity presented some challenges. Vessels ‘pushing the dock’ have a significant impact on battery sizing, so finding an alternative is worth consideration. Shore-side infrastructure, including dock positioning, needs to be considered as part of the overall charging power plan.”

In EBDG’s view, for hybrid or electric vessels, the volume of cabling required will necessitate early coordination and detailed routing strategies. Parasitic loads from battery installations are another important factor that must be planned for in the design phase.