New Cat® Hybrid Propulsion Package Powers First Two U.S. Tugs and Signals Future

Hybrid Propulsion powers tugs
Hybrid Propulsion powers tugs

Two new ship-assist tugs delivered to Harbor Docking & Towing (HDT) in Lake Charles, La.—the Ralph and the Capt. Robb mark a significant departure from HDT’s other tugboats and preview the future.

Harbor Docking & Towing cited two key reasons for choosing a new path and departing from the norm in their fleet of five existing tugs.

First, at 93 ft, the shipyard’s tugs are a good match for the Calcasieu Ship Channel, which John Buchanan, HDT’s president describes as “a little tight in places.”

Washburn & Doughty was “willing to entertain the Cat® hybrid partnership,” Buchanan says. “And we saw it as the future.”

The Capt. Robb and the Ralph are the first two tugs in the U.S. with a hybrid propulsion system developed in cooperation between Caterpillar and Berg Propulsion. It consists of a pair of 2,550-hp Tier 4 Cat 3512E marine propulsion engines plus two ABB electric thruster motors, each rated at 800 hp and the Berg Propulsion MTA 628 azimuthing thrusters and hybrid control system.

“The Hybrid configuration that resulted from our partnership truly delivers best of breed performance.  The ability to transit on a single small unit greatly reduces CO2 and emissions, while the power mode provides outstanding transient response required in narrow harbor operations,” said Caterpillar Marine product manager, Jon Jackson.

Completing the hybrid package are two 565-ekW Cat marine generators and a single 200-kW Cat C7.1 genset for on-demand electrical power to the Cat MTA 628 Z-drives. Batteries are not required for power storage.

The power management system has several modes that automatically control the number of engines online. The eco or electric mode is for traveling to and from jobs with the generators powering the electric motors. Eco mode allows the vessel to transit on a single C18 engine, providing fuel economy advantages as well as reducing hours on the main engines. If power demand of the vessel increases, a second C18 will come online automatically. The second C18 will seamlessly go offline once the power demand decreases, allowing for an ideal mix of response and fuel economy.


“That’s very smooth and quiet,” notes Buchanan, “and you can really finesse your maneuvers.” 


The mechanical mode runs only the main engines, while the power mode uses the main engines, generators and electric motors.

In FiFi mode, the starboard main engine powers the firefighting pump that sends water to two remote-controlled Fire Fighting Systems (FFS) 1200 monitors. The electric motors provide station keeping or propulsion.

There’s a fair amount of automation on the tugs. For instance, the engines will start and stop on their own. When going from eco mode to power mode, tap a button on the bridge, “and the two main engines start up on their own,” Buchanan says. With just under 700 monitors on the boat, “there was a learning curve, but the boats are so automated that it’s actually easier for the crew to run.”

Don’t be surprised if more tugs adopt this hybrid propulsion package. “A lot of folks waited to see how these were going to prove themselves,” Buchanan says.

HDT has had several tug companies look at the Ralph and Capt. Robb

“They were very impressed,” notes Buchanan. “If we build again, more than likely we will stick with this propulsion.”

The vessels were recognized as part of WorkBoat’s “10 Significant Boats of 2020.”

Learn more about the revolutionary new Hybrid Propulsion Package by visiting with the experts at your local Cat Marine dealer and Berg Propulsion distributor.