The green and white tug Carolyn Dorothy slipped past the Foss Maritime office on Pier D in Long Beach, performed a graceful, smokeless pirouette and continued out into San Pedro Bay with no more sound than a well-paddled freight canoe.
At that time in March 2009, she was on her way out to one of her first ship-assist jobs. But, as the first hybrid tug in the world, this one could be forgiven a little showing off, especially when it was done so quietly.
Most tugs cruising past the Foss headquarters on Pier D would do so with both engines running at low rpm and a generator droning away as well, just to produce electricity. Carolyn Dorothy, to prove a point, did so under battery power alone — her main engines were shut down on standby, while the generator was running just to feed power into the batteries. Welcome to the world of hybrid propulsion.
Here is a new tugboat, 78 feet in length with z-drive propulsion, that can cruise on just battery power or on direct shafted power from her main engines, exerting more than 5,000 hp when needed. The beauty of her system is that she can choose combinations of power sources for propulsion — including the auxiliary generators — or apply them all together for periods of maximum power, and it's all controlled by a computer designed to maximize fuel economy and minimize exhaust emissions from diesel engines.
"If you run this boat the way it's supposed to run then we save emissions that would go into our kids' lungs," said Jerry Allen, Foss' port engineer for Southern California.
Foss is the first marine company in the world to build a viable hybrid workboat. At her simplest, Carolyn Dorothy is described as the 10th in a series of Dolphin-Class z-drive harbor tugs built at the Foss shipyard in Rainier, Ore. It is what's down in the engine room, however, that makes her unique.
Many companies are working on hybrid designs to meet or head off the blitz on emissions, particularly in the harbors of Europe and the U.S. Some of these new hybrid designs involve combinations of marine diesel, liquefied natural gas (LNG) and storage batteries. However, the large space required for tanking LNG aboard a tug is presenting some engineering problems with that tack. But it was just a couple of years ago when the weight of large banks of batteries was considered a design impediment to development of the first Foss hybrid tug. Today the 126 12-volt, gel-cell storage batteries weighing about 18,000 pounds stacked into the engine room of Carolyn Dorothy seem to be just another part of the ballast system.
As a starting point in the design process, Foss engineers used computers to track the operating patterns of two other similar tugs working in the Long Beach/Los Angeles harbor. Ultimately, it was determined that the tugs needed full power for only 7 percent of their operations. However, when full power was needed it was needed immediately. The study also showed that the tugs operated about 95 percent of time at less than 67 percent of total power, and that they operated roughly two-thirds of their time at less than 20 percent power.
Inherent in a hybrid design are the fuel savings and lowered emissions that are achieved at low power, the mode most utilized by harbor tugs.
The power formula presented by Carolyn Dorothy integrates smaller, lighter diesel main engines and larger diesel auxiliaries than the existing Dolphin tugs, along with storage batteries and with a motor-generator located between the engines and the z-drives. The motor generator (MG), located just aft of each main engine, does not create power on its own. Rather its function is to convert electric power (from batteries or generators) to mechanical power (turning the shaft) and the opposite, depending on operating mode. The MG can be clutched in or out of operation.
The specific power train is as follows: two 1,700-hp Cummins main engines, two 310-kW Cummins auxiliary generators, 126 batteries, carbon fiber shafts, two Siemens motor-generators and, finally, two Rolls-Royce azimuthing stern drives. A large switchboard and DC bus is housed within a cabinet located between the main engines.
"The challenge of harbor towing operations is that the tugs spend 95 percent of their time at very low power, waiting to apply 95 percent of their power for less than 5 percent of the time," said Robert Allan, the Vancouver-based naval architect whose company helped design the new Foss hybrid tug as well as the nine other Dolphin tugs before her. "With this combination of components the tug can operate on any combination of batteries alone, gensets alone, batteries plus gensets, main engines alone, or engines plus batteries, according to the power demand," said Allan.
When full power is needed, the full power of main engines is used to turn propeller shafts and a quick boost in shaft torque can be applied through the motor generators from both battery bank and auxiliary generators. The result is applied power of up to 5,080 hp with bollard pull of 60 tons — the same power standards built into the entire class of Foss Dolphin tugs.
The hybrid system adopted in Carolyn Dorothy is the creation of two Canadians — Jason Aspin of Aspin Kemp & Associates (AKA) and John Eldridge of XeroPoint Energy (XPE).
The pair attended the Canadian Coast Guard College together and established a rapport revolving around so-called green technology in the marine environment.
"AKA is a system-integration company that provides high reliability power, propulsion and control systems for industry where system failures cannot be tolerated, i.e. DP Platforms, Ferries, etc.," said Aspin. "John Eldridge and I came up with the hybrid design that was the basis of the Foss system in 2004."
Aspin said they set up XPE to focus on green energy solutions. "We had put together a system for a small eco-tour vessel. The intent with our design was to have a very flexible power system that could be used in any power plant (shore or marine). Essentially for the Foss job we super-sized the first design and then tailored it for their vessel and duty cycle. The technology seemed to be an elegant solution to reduce air emissions through increased efficiency and lower fuel consumption. We did the detailed engineering design and manufacturing of the system as well as the installation and commissioning.
At its heart, the new tug can still use her main engines to turn shafts that will rotate the azimuthing propellers. Beyond that it's all kind of a tugboat makeover, made possible by the Siemens motor-generators, the large bank of batteries that store electricity, the switchboard and the computer that regulates and applies power where and when needed.
Every diesel has the ability to put power on the DC bus to supply either or both MG sets for propulsion as well as critical auxiliary loads such as hydraulic pumps, cooling pumps and the winch," said Aspin. "Any engine or power source can also feed the whole system for general hotel needs."
Yes, even the winch design gets into the act. Carolyn Dorothy is equipped with a Markey DEPGF-42 winch on her bow — a winch similar to that found on other Dolphin tugs except for its hybrid contributions. The tug's power system can accept regenerated power from the Markey winch.
The DEPGF-42 hybrid winch is especially configured to generate power back to the batteries when the winch is rendering. The motor acts as a generator," said Blaine Dempke, president of Markey Machinery Company of Seattle. "Tug power is used when the winch is recovering."
Essential to smooth and continuous operation of the system is the computerized energy management system (EMS).
The EMS is designed to prevent the captain's mind from forming into a Gordian knot, by reducing all possible combinations of power into four power bands and automatically configuring power sources to the propulsion and hotel loads required according to demand. These power bands are given user-friendly labels such as Minimal Emissions, Eco-Cruise, Mid Range and Full Power.
The captain or watch-standing operator chooses whichever of the levels is appropriate — stop, idle, transit or assist, all arranged on a small panel in front of him. Then as he makes demands on the z-drives via the joystick, winch controls, etc. The system kicks in with the required power plant combinations.
As well as making things simple for the captain, the bands are designed to automatically conserve the most fuel and emit the least emissions for each mode of power required.
For example, in the stop mode, when the vessel is idling between assignments and/or using less than 5 percent of her propulsion power, the power configuration is typically for one or two auxiliary generators running and stored energy available for use.
In the transit mode, for continuous slow transit and low power work using less than 22 percent loads for extended periods, a typical plant configuration is one main engine and two auxiliary generators running. One main engine on one driveline and a powered MG on the opposite side provide propulsion. The system permits both ASDs to be operated by one main engine. Battery power can be used as a temporary ride-through of transient demands.
In the assist mode, during continuous fast transit and a large percentage of ship assist work where maximum power requirements do not exceed 46 percent for extended periods, the typical configuration is two main engines. If the batteries need recharging in this mode, one or both auxiliary generators will kick in.
Full power is for continuous fast transit and full power ship assist work. A typical configuration is two main engines plus two auxiliary generators with battery-stored energy available to reach full power and most transient demands. The plant is also capable of providing full shaft horsepower for propulsion.
Mike Lonich, first assigned captain of Carolyn Dorothy, says he enjoys the distinction of his unique position.
"She's just like the other Dolphin tugs when she's in the assist mode. But, there is a lot of difference when she's in the transit mode and hybrid mode. She's pretty quiet. In the idle mode, when we're waiting for a ship on batteries only, or when we need just enough power for keeping on station, there is no (motor) sound. All you hear is the vents and the AC."
Fuel usage is estimated to be 20 to 30 percent less than the standard Dolphin tugs, said Port Engineer Jerry Allen. "It will take a year to get real numbers, but I think we're going to see better than that. We'll make these numbers for sure. We went all the way down to San Diego for her christening ceremony, traveling at 6.5 knots and powered by just one generator feeding energy into the system.
The cost of the tug is still a work in progress. It is estimated that the first hybrid will add 40 percent to the cost of a standard Dolphin tug. Cost of a typical ship-assist ASD tractor tug nowadays runs between $7 million and $10 million. The $1.3 million contributed by the ports of Long Beach and Los Angeles will not cover the total difference in cost, estimated at roughly $2 million.
However, Foss officials report they anticipate realizing savings through reduced fuel usage, maintenance of machinery and extended engine life. The hybrid has already generated considerable goodwill for the company, and that could translate into a marketing advantage, particularly in West Coast ports.
However, there are benefits for Foss to harvest, such as the above mentioned annual fuel savings and the expectation that the mains will turn half as much as the existing Dolphin tug engines do, annually. Twice the engine life is a significant benefit, as is good will, both in reference to the ports, but also to the citizens of Long Beach and Los Angeles with the company's contribution to a quieter, cleaner environment.
While Foss says it has no immediate plans to build another hybrid tug, the company said it will likely develop plans to retrofit some of its existing tugs after it learns enough about operations of the new technology.
The newest Foss tractor tug includes a hybrid power package that encourages minimum power usage during time between jobs or for other periods of light duty.
