Hybrid propulsion: A viable tug option

“These new tugs are like sports cars and Mack trucks all rolled into one,” John Buchanan, president of Harbor Docking and Towing Co. LLC, Lake Charles, La., said as he kicked off the Tugs and Coastal Towing Program at the 40th International WorkBoat Show in New Orleans on Wednesday.

Buchanan was describing the Ralph and the Capt. Robb, 93’x38’x15.5’ tugs that the company has been running on the Calcasieu Ship Channel since this summer. The boats, built at Washburn & Doughty in East Boothbay, Maine, are the first two tugs in the U.S. with Caterpillar hybrid propulsion systems. These make the boats both extremely powerful and immensely responsive. Buchanan said he sees hybrids as a viable option for the tug industry going forward because they are more economical and efficient to operate.

A pair of Tier 4 2,550-hp Cat 3512E main engines plus two ABB electric thruster motors, rated at 800-hp each, power the tugs. Completing the hybrid package are two 565-kW Caterpillar 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.

There are four power modes: an eco mode for traveling to and from jobs with the generators powering the electric motors, a mechanical mode that runs just the main engines, a power mode for ship work that uses the main engines, generators and electric motors. There is also a firefighting mode.  Everything is operated via touch screen, and the modes can operate automatically, powering up or down as needed.

The electric motors allow the tugs to avoid what Buchanan said are “some low-torque issues in conventional Tier-4 designs.” The electric motors give “immediate torque at the low-end (allowing) the 3512 to spin up faster and allowed us to go with smaller main diesel engines without sacrificing bollard pull.”

Buchanan said they went for hybrid power because they were looking for a technology that matched their needs in the tight and twisty 35-mile long Calcasieu Ship Channel that connects the Port of Lake Charles to the Gulf of Mexico. “We wanted high horsepower – at least 80 metric tons of bollard pull – for moving ships, but we only use that a small percentage of the time, and this system allows us to scale up and scale down. We can transit a light boat under 7 knots running one generator, burning just 22 gallons of fuel. Contrast that with full power, burning 326 gallons an hour, pushing and pulling at 100%.”

The benefits of a hybrid system, Buchanan said in summary, are quick throttle response from the thruster motors, better escort maneuverability in tight channels, fewer running hours on the main engines which means reduced maintenance, minimum fuel burn in transit and increased redundancy.

The Ralph, which is moored at the Julia Street wharf in New Orleans, is open for visitors for the duration of the WorkBoat show.

About the author

Betsy Frawley Haggerty

Betsy Frawley Haggerty, a USCG licensed captain, has been a maritime journalist for more than 30 years. Her work has appeared in Offshore (where she was editor for seven years), Soundings, Professional Mariner and Workboat, among other publications.

1 Comment

  1. Avatar

    I like how you explained that electric motors allow a tugboat to have immediate torque. Having torque at the beginning allows the boat to be able to pull the larger boats without sacrificing much bollard pull. I think this is really interesting because these tugboats are able to pull ships that are much larger than they are. I imagine how dangerous this job could be so I am glad that professionals are always behind the controls and doing it to keep people safe.
    http://www.ausbarge.com/our-services/

Leave A Reply

© Diversified Communications. All rights reserved.