Caterpillar Marine, Houston, is developing a production battery system for hybrid and fully electric vessels, targeting applications ranging from harbor tugs and ferries to inland workboats.
In a fully electric configuration, the CAT marine battery system supplies the primary energy for vessel propulsion. In a hybrid installation, the batteries operate alongside Caterpillar engines, generators and other powertrain components, the company told WorkBoat.
The first production application uses lithium iron phosphate (LFP) chemistry. The liquid-cooled system has a 1C charge-and-discharge rate, operates at voltages up to 1,420 VDC and can be arranged in multiple rack configurations to fit within a vessel’s battery room.
“We are developing a range of battery modules covering chemistries adapted to most duty cycles, with LFP as our first marine production application,” said Will Watson, marine product director at Caterpillar.
Caterpillar expects tugs and ferries to be among the strongest candidates for the system because they generally operate close to shore, experience variable power demands and may have regular access to charging infrastructure.
“Beyond tugs, the CAT marine battery system is suited to additional segments including ferries and inland vessels,” Watson said. “Every vessel is different and requires a customized approach specific to the application.”
Tugs that alternate between high-power ship-assist work and periods of low-load operation or idling are among the earliest adopters, according to Watson. Pushboats and inland towboats could transition more gradually because of their continuous power requirements and long operating lives.
“The strongest adoption we are seeing today for fully electric energy rooms is in the tug and ferry space: operations that stay close to shore and have variable power demands,” Watson said. “That duty cycle is adopting hybrid at a higher rate than constant-load vessels.”
Point-to-point vessels and inland vessels with shoreside charging access also lend themselves to increased electrification. Hybrid systems may remain more practical for vessels operating at constant loads, over longer ranges or in areas with limited charging infrastructure.
“Where duty cycles are constant or charging access is limited, a hybrid configuration is often the better fit,” Watson said. “Power options that include batteries and lower-carbon-intensity fuels are a way to modernize assets while avoiding heavy CapEx investments that are tied to the uncertainty of certain fuel economics and availability. Engine and battery technologies can be mutually supportive, and it’s important to design a path forward that aligns a vessel’s planned use with a vessel operator’s objectives.”
Caterpillar describes that approach as the transition from a conventional engine room to an “energy room,” in which engines, batteries, generators, electric motors, power electronics and controls operate as an integrated system.
“We can transform conventional engine rooms that are powered by CAT's range of diesel-powered marine engines into hybrid systems that combine our propulsion engines with electric motors, clutches, gensets, power electronics, controls and batteries,” Watson said. “The battery system works with CAT engines only, not third-party engines.”
The battery system can operate independently in a fully electric installation and provides additional benefits when incorporated into a complete Caterpillar hybrid system, Watson said.
Newbuild and retrofit applications
Watson noted fully electric installations are generally easier to incorporate into new vessels than existing boats because of the space, weight, cooling and electrical requirements associated with a marine battery system.
“It’s typically challenging to install a fully electric power system as a retrofit,” Watson said.
Caterpillar is advising operators to consider future propulsion requirements while designing new vessels, even if they are not prepared to transition immediately to fully electric propulsion.
“We’re advising operators that a modest CapEx investment when building a new vessel can provide long-term flexibility,” Watson said. “As operators plan for newbuilds, we’re seeing a growing number incorporate fully electric 100% marine battery-powered systems. However, many operators are continuing to incorporate hybrid powertrain options in newbuilds to allow them more flexibility.”
Retrofits could still allow operators to lower ownership costs and extend the useful lives of existing vessels, Watson said. Each potential project, however, requires a review of the vessel’s design, configuration and operating profile.
“Given operators’ substantial investments in their existing fleets, retrofits enable operators to achieve a lower total cost of ownership and maximize the ROI with their current vessels,” Watson said.
High-power performance
The CAT battery system is designed to respond rapidly during towing, acceleration, dynamic positioning and other high-power operations.
“The marine battery system is capable of discharging energy much faster than traditional batteries,” Watson said. “This enables the system to deliver instant torque and crucial stabilization when operators need it.”
In a hybrid configuration, the battery can respond to sudden load changes while the vessel’s engines increase output.
“This eliminates the lag that’s experienced with conventional systems, and it enables main engines to ramp up without risking a blackout,” Watson said.
Each battery module is sealed, and its liquid-cooling circuit is isolated from the module’s interior. The system also incorporates leakage detection. Caterpillar’s battery management system continuously monitors cell and module temperatures, charge levels and battery health.
“Our battery module is liquid cooled to maintain optimal cell temperatures and protect battery health during high-power maneuvers,” Watson said.
The rackable configuration allows Caterpillar to tailor the number and arrangement of modules to a vessel’s power requirements and available space. The 1C rate means a battery could be charged in about one hour, although actual charging times would depend on the installation and available charging capacity.
“The CAT marine battery system supports efficient charging with a 1C charge and discharge rate,” Watson said. “With this technical specification, a battery could be charged in approximately one hour, depending upon specific configuration and vessel requirements.”
Caterpillar is designing the systems around vessel drydock schedules, with battery replacement initially targeted at intervals of approximately five years, followed by 10 and eventually 15 years as the technology develops.
“Correctly matching a battery to how a vessel is actually operated and its specific application is key to maximizing battery life,” Watson said. “We’re designing these systems to align with vessel drydock cycles, with replacement targeted at roughly five, then ten, and eventually fifteen years.”
Service and certification
The system is serviceable at the module level. Fuses, contactors and electronic control modules can be serviced onboard by qualified technicians with specialized training and tooling.
“The battery system is serviceable at the module level, with spares such as fuses, contactors, and ECMs serviceable onboard,” Watson said. “The CAT Battery Management System, combined with add-on telematics, provides monitoring, alerts, faults, and prognostics that help operators plan service events and minimize downtime.”
For hybrid vessels, using batteries to manage variable loads can allow engines to operate closer to their most efficient range, reducing fuel consumption and engine wear.
“For hybrid systems, operating the combustion engine in its optimal range reduces wear and fuel consumption and extends engine life, which factors into hybrid payback,” Watson said.
The system is IEC compliant and CE certified, according to Watson. Caterpillar is also pursuing approvals from the major marine classification societies.
“We’re also targeting compliance with ABS, DNV, BV, RINA and Lloyds,” Watson said.
Caterpillar has not opened a public order book for the system. Operators interested in pilot projects or early applications are being directed to their Caterpillar Marine account managers.
Watson said commercial marine charging and hybrid systems remain largely customized, but he expects greater standardization as adoption increases.
“Hybrid systems are still in a custom phase,” he said. “Over time, more standardized production options will emerge, as they did with conventional engines.”
Caterpillar expects batteries to form one component of a broader marine energy mix that includes conventional engines and engines capable of operating on lower-carbon fuels such as biofuels and methanol.
“Given the broad range of operating conditions, variances in fuel availability by region and vessel operator goals we encounter, Caterpillar Marine anticipates a multi-energy future for workboats,” Watson said. “Flexibility is key which is why we offer a comprehensive suite of solutions from combustion engines that can operate on lower carbon-intensity fuels (including biofuels and methanol) to hybrid powertrains to fully electric power systems.”
“No single solution fits every vessel, which is why we customize each power system to be ideal for not only the vessel but also how it’s operated and its purpose,” he added.
