Another milestone for hybrid workboat technology has been delivered on the West Coast: the 100’x40’ tugboat Delta Teresa, the latest tractor tug for San Francisco-based Baydelta Maritime.
It’s the seventh tractor tug that Nichols Brothers Boat Builders, Freeland, Wash., Seattle, has built for Baydelta, but a dramatic departure with its dual diesel-electric propulsion system.
Designed by Jensen Maritime Consultants, Seattle, the hybrid concept as applied to tugboats aims to deliver on several fronts: reduced air emissions, lower fuel and maintenance costs, and boosted bollard pull on demand.
Delivered April 16, the Delta Teresa is the first to use Rolls-Royce propulsion units in the U.S. to take power from electric, diesel or both power sources. That energy comes from both two Caterpillar C3516 C Tier 3 diesel engines, rated at a total 5,350 at1,600 rpm, and by two 424-kW electric motors.
The Z-drive system of two Rolls-Royce (recently acquired by Kongsberg) 255FP units, can accept power from the diesel engines, electric motors and from both power sources. The electric motors are powered by three Cat C9.3 300-kW each, 480V 3-phase at 1,800 rpm generators, plus one harbor generator, a C7.1 150-kW 480V, 3-phase at 1,800 rpm.
The hybrid system, allows for the vessel to operate in different power modes, direct-diesel, diesel- electric or fully-electric. The hybrid concept allows fuel savings and reduced exhaust emissions, while supplying Baydelta with the same power and vessel characteristics needed for their operations.
During trials the tug’s performance met or exceeded all expectations. Free running speeds, under full power, of 14-plus knots were obtained along with almost 10 knots on electric motor power only.
The flexible drive system will allow the tug to make transits and loiter at speeds up to 7 or 8 knots in its electric-only mode. In combined diesel-electric mode, the additional electric power input will lend an additional 9 short tons of bollard pull for a total 90 tons. Jensen designers say that’s a new way to squeeze more horsepower into new model tugs, now at the 100’ hull length standard to deal with the new generation of ultra large container vessels (ULCVs).
There are accommodations for up to seven crew. Deck equipment includes a Rapp Marine electric hawser winch, and a single drum tow winch, with the drivetrain connected with Centa carbon fiber shafts. In addition to the drive units and hybrid system, Kongsberg supplied the control system and main switchboard, electric motors and their control cabinets.