By Jillian Mitchell


Carolyn Dorothy, the world’s first hybrid tugboat, is efficient, green, and quiet. Since her Long Beach launch in early 2009, this femme fatale has caused major buzz in the marine industry, and, three years later, her en vogue status continues to reign, as countless hybrid vessels now trend the waters.

For many, hybrid tugs like Carolyn Dorothy offer much appeal. But, for others, the question still remains: can hybrids really outperform their conventional competitors?

Grant Brown of Corvus Energy Limited says yes.

“Imagine a big diesel generator (capable of lighting up an entire office building) that powers only one 60 watt bulb, 24 hours a day. Now imagine the same generator charging a battery, which, in turn, powers the bulb. When the battery is charged, the generator shuts off and the battery lights the bulb, and when the battery gets low, the generator starts up and recharges it,” says Brown, the company’s director of marketing. “This latter system is comparable to a hybrid system and is the ultimate in efficiency, reducing fuel costs and emissions and lowering maintenance cycles.”

By simply installing a battery into the system, fuel consumption is reduced dramatically, he continues. Further, this battery allows the diesel to now operate at higher efficiency, reducing pollution from low-speed operation—and, of course, the hours of operation and maintenance in a calendar year.

Moreover, hybrid tugboats are perfect applications of hybrid drivetrain technology, which is currently available in two types: hybrid light and full hybrid.

Commonly used in vessels being retrofitted from straight diesel, hybrid light is the cheapest and easiest way to gain the benefits of a hybrid immediately without building a new boat, explains Brown. The hybrid light consists of a traditional drivetrain layout of two large diesel engines providing motive power to the propellers, and a smaller genset to provide house power. Hybrid operation is achieved with the addition of a battery pack and another genset providing power to electric motors (which are installed on the drive shafts between the propellers and the engines).

Hybrid batteries.

Hybrid batteries.

“In transit, at idle, on the dock or any other low power times, the vessel is run by batteries. If the batteries become depleted, a generator will automatically recharge them. If the load exceeds the generators capacity to recharge the batteries, then the second generator joins in, powers the load and recharges the batteries,” says Brown. “When the duty requirements of the vessel exceed the capacity of the battery system (and the two generators), the diesel main engines start, the generators shut down, and the vessel is run on full-diesel power.”

Brown adds that during a full power or emergency situation the captain may add the power of the electric motors to the diesel mains for a full-on, full-power event. As the entire system is controlled by computers, it is a seamless integration of the two technologies for the operator.

Next, a full hybrid is a much more efficient method and is the system being designed into new vessel builds. In these vessels, the system is designed from scratch as a hybrid and consists of a large diesel generator powering a battery pack, which in turn powers electric motors that provide propulsion. Inherently simpler, this system relies entirely on the batteries to provide the power and achieves a significant fuel-consumption reduction.

A main appeal of the hybrid systems is the reduction of carbon emissions. Most hybrids eliminate low-speed operation when the diesels operate at their lowest efficiency and a larger proportion of the fuel is not combusted fully, resulting in lower emissions. Succinctly, the hybrid light system achieves a 25 to 30 per cent fuel savings, compared to that of a full hybrid at up to 50 to 75 per cent (figures compare to a conventional diesel).

A refit is the perfect time to upgrade to hybrid—specifically due to the fact that a tugboat, with a life span of 40 years or more, must have the engines replaced every four to five years, or about 20,000 hours. In most cases, the fuel savings alone will pay for the cost of conversion in three to five years, says Brown. These hybrid systems offer a 20-year lifespan, or about 83,000 hours (“a compelling rationale to convert to a Corvus-powered hybrid,” he says).

As a means to encourage the green initiative, there are many local and federal grants available to owners and operators, as well as other initiatives such as low-interest loans and leasing options. The challenge, says Brown, is that these opportunities are not always well advertised. As a solution, Corvus Energy has a full-time employee who is available to help customers find the “hidden money”.

Undoubtedly, conventional tugs are far more prolific—there are only a handful of hybrids worldwide with more in progress being built. As this technology becomes more accepted by industry, Brown believes it will gain momentum.

“Due to increasing global fuel costs, we believe that in 20 years the vast majority of commercial work boats of all types will be hybrids,” says Brown. “Commercial operators are generally very conservative in their adoption of new technology, especially one that has such a big impact to their operation. They need assurances that the technology will work as advertised, and thanks to early adopters, such as Foss Maritime in USA, Siemens in Europe, and Kotug in Holland, we are getting the validation.”