Hybrid Harbor Tug Launches

On January 23, Foss Maritime Company will launch its hybrid tug in San Pedro Bay.
“It’s the world’s first hybrid harbor tug and Foss’s latest initiative to reduce our emissions profile,” said Susan Hayman, Foss vice president of corporate development, speaking at the CBN Southwest Intermodal Conference.

Choosing the Tug

Foss, a large West Coast-based tug and barge company, has already proven itself a leader in environmental stewardship — voluntarily switching its entire fleet to ultra-low-sulfur diesel — and it is the first transportation company to be accepted into the EPA’s Smart Way Transport program for its maritime operations.

Hayman said it made logical sense for the company, which is committed to reducing fuel consumption and greenhouse gas emissions, to gravitate toward a hybrid technology. The tug was the natural choice.

“To deliver the required high thrust levels, tugs are equipped to develop very high horsepower, but they very seldom use it. They usually operate in the low and inefficient part of their power range,” said Hayman. “Because their business has attributes of hurry up and wait, many of our tugs spend the majority of their time at low power or idle. The beauty of hybrid technology is that it optimizes the power sources — in our case, its main engines, generators, and batteries to run only when needed.”

Retrofit or Build New

Once Foss chose the tug, the next decision was whether to retrofit an existing tug, or incorporate the hybrid design into a new-build tug. The company chose the latter.
“We chose this route because of the flexibility a new-build would allow and the fact that we build these tugs at our own shipyard in Rainier, Ore. We would have the ability to closely monitor and control the building process and really design this tug for maximum emissions benefit.”

Tugboat Dilemma

When designing the new tug, Hayman says they looked closely at detailed information they downloaded from tugs currently operating in the San Pedro Harbor. The data demonstrated that actual percentage load on the main engines was only at about 16 percent overall.

“This means that these harbor tugs spend the majority of their time at the very low end of the engine’s power curve. However, there are times when the tug needs almost its full horsepower, but it tends to be for very short periods,” said Hayman. “It’s sort of like owning a Ferrari and only driving it around downtown city traffic. It’s really not what the engine wants to do and doesn’t make it happy.”

When engines aren’t running at optimum efficiency, they emit higher emissions. In fact, emissions are directly related to both the amount of fuel consumed and the efficiency of the combustion.

“In the hybrid, we have the double benefit of reduced consumption and more efficient combustion, because the engines are running at their peak efficiency,” said Hayman.

Designing the Tug

In designing the tug, there were limitations. For example, the hull design could not be changed, and the equipment (including 18,000 pounds of batteries) had to fit within a very small engine room.

“We needed to retain at least the same redundancy as with a conventional tug, and indeed this tug has increased flexibility and redundancy,” said Hayman. “We also knew that we had to deliver the same horsepower and the same bollard pull as with a conventional Dolphin tug.”

She says the new design not only retains that, but also enhances the safety and redundancy aspects of the conventional tug.

“It [has] smaller main engines, auxiliary generators, decoupled propulsion, motor generators, and a battery bank. The tug has vastly increased flexibility in machinery configurations.”

Hayman added that there are 32 possible combinations of battery, auxiliary generators, and/or main engines, which is vastly superior to a conventional tug.

There were no changes in the propulsion system. But what the hybrid has that the conventional Dolphin does not, are two 1,200 horsepower motor generator sets and a 600 horsepower battery bank. The hybrid tug operates in 4 power bands that are seamless to the operator.

• Minimal emissions
• Echo cruise
  
• Mid-range
  
• Full mode

Hayman said Foss used the data from the sister Dolphins to estimate the percentage of operating hours the tug spends in each mode. Based on the data, 65 percent of the time is spent in the minimal emissions mode — 0 to 5% power range — during idle periods of low speed/no wake maneuvering. It is during this mode the main engines are off-line and the tug uses the batteries for the hotel load and station-keeping maneuvering. An auxiliary generator comes on as needed to recharge the batteries.

The other modes use a combination of batteries, generators, and main engines — depending on the power requirements.

Benefits of Hybrid

The benefits of the new technology are numerous:

• Better fuel consumption — 20 to 30 percent
  
• Reduced emissions
  
• Ability to use shore power
  
• Reduced life cycle costs — engines accumulate zero operating hours while idling.
  
• Reduced noise
  
• Can be retrofitted into other tugs
  
• Can make use of future power sources, such as advances in battery technology or hydrogen fuel cell technology

With all these benefits, why isn’t everyone building one? Hayman says it’s probably due to increased capital costs.

“Although the benefits of cleaner air to the residents of the communities we serve are of incalculable value, we can calculate the cost of a hybrid tug. And in our case, the hybrid will cost approximately an incremental $2.5 million when compared with a conventional tug,” she said.

Another reason is that emissions benefits and fuel consumption savings are dependent on the duty cycle, which Hayman said are often different depending on the operation.
“San Pedro happens to be an ideal place for hybrids because they are short transit runs and considerable amounts of time at idle. Although there are still benefits of this application for other things, like ocean towing boats, they’re not as great, because the tugs tend to operate at higher horsepower for longer periods of time.”

Lastly, Hayman said the hybrid tug does require increased engineering efforts. “Any new technology bears the burden of higher engineering and design costs. We do expect the costs of the hybrid technology for future applications will decrease over time, as hopefully it will be more widely adopted.”

The Future of Hybrids

Whether it’s adopted will depend, in part, on the tug’s successful launch. From the buzz around the event, the mood is optimistic.

“We really hope that this will mark the beginning of a significant trend in our industry,” said Hayman. “But for us, it’s a natural progression to reduce our emissions profile.”