Question: While it may look like a standard tugboat, the Carolyn Dorothy is anything but. In fact, this tenth vessel in the line of Dolphin-class tugs operated by Seattle-based Foss Maritime is a hybrid tug, the first of its kind in the world. Its power system includes two
diesel generators and two diesel engines; electric motorgenerators; and 126 12-volt lead-acid batteries weighing 18,000 pounds. The boat can operate off the batteries only, off the power of one or more generators or engines, or a mix of sources. This highly variable combination allows the Carolyn Dorothy to match the power needed to the task at hand. Founded in 1889, Foss Maritime began with a single used rowboat and grew into a global maritime empire whose services play an important role in the supply chains of numerous industries, from bridge construction to logging. In the spirit of continuous improvement, Foss has long desired to build a cleaner, more fuel-efficient tugboat-one that helps the company minimize toxic emissions and energy use. Recently, in collaboration with an engineering firm, it devised a way to adapt a standard, "off-the-shelf" power system and combine it with battery technology to create a hybrid tugboat. Foss began by analyzing how tugs typically operate.
It discovered that 60 percent of the time, tugs need less than a fifth of their power, and 95 percent of the time, less than two-thirds of their power. What's more, their diesel engines operate at fuel efficiency only when used at the top of their range. After considering (and rejecting) several alternatives, Foss consulted with Aspin Kemp & Associates, a Canadian engineering firm that builds specialized systems for oceangoing vessels, drill ships, and semi-submersibles. Together, the firms fashioned a new methodology. Like a typical tug, the Carolyn Dorothy has four engines-two big ones for heavy loads and two smaller ones for auxiliary power. However, unlike a typical tug-where both large engines must operate simultaneously to balance the ship's load-it can use a single small engine to power the whole boat at low speeds. A computerized system allows the captain to switch seamlessly between hybrid and conventional power. Foss has not yet calculated the exact return on its investment, but it knows one thing: the hybrid performs better. Using about 30 percent less fuel, its greenhouse gas emissions are also reduced. Early tests suggest its nitrous oxide emissions are cut nearly in half, with carbon-dioxide and sulfur-dioxide emissions reduced by as much as 30 percent. The boat is quieter, too. And because the main engines work less than those of standard tugs-about half the number of hours per year-the hybrid tug has lower lifecycle costs. Another plus: while Foss expects to replace the Carolyn Dorothy's batteries three to five years from now, it believes that advances in battery technology will provide a greater choice of replacement options. Meanwhile, the company is giving serious thought to retrofitting its other Dolphin-class tugs with the hybrid technology.
1. Foss Maritime earned ISO 14001 certification for its commitment to such environmental goals as reducing fuel consumption and vessel emissions. Does this credential offer a differentiator for the company? How should Foss use this information in marketing its services?
2. With other firms' expressing interest in the hybrid technology, Foss and Aspin Kent are considering a joint venture to sell the technology, and have a patent pending. What other applications, besides tugboats, may be feasible? Sources: Bruce Buls, "Crossbreed: Foss Maritime's Carolyn Do.