Tugboats are in a strange position in the marketplace: there are enough of them out there to suck down a fair amount of fuel in port cities, and to cause some medium-sized problems for local air quality. But there aren’t quite enough of them for manufacturers to build engines specially designed for tugs’ needs.
So tugboat manufacturers typically outfit their ships with maritime versions of locomotive engines: hulking machines with enough power to pull big loads. A good-sized harbor tug has two of these massive engines running, along with an auxiliary motor or two to provide power for on-board equipment, even when it’s just tooling around the harbor at the pace of a brisk walk. Unfortunately, locomotive engines are pretty darn inefficient at slow speeds and light loads—which is precisely how harbor tugs run most of the time. Tugboats wind up wasting a lot of fuel as a result, which boosts their climate-warming emissions while hurting the tugboat operators’ bottom lines.
Enter Foss Maritime. The storied, Seattle-based marine transportation company has figured out a way to adapt off-the-shelf engine and battery technology to create a cleaner, fuel-saving hybrid tug. The company’s still waiting for data from its lone hybrid—which was constructed in their Rainier, OR shipyard, and is now stationed in L.A./Long Beach—but expects that the hybrid technology will save the company a bundle on fuel.
Finding this article interesting? Donate now to support our independent research!
I met with Susan Hayman, the Foss VP who spearheaded the hybrid tug project, a few weeks back to discuss some of the hybrid’s technical features. Like a regular tug, she explained, the hybrid has four engines: two big ones for heavy loads, and two smaller ones for auxiliary power. But unlike a typical tug—whose two main engines must run simultaneously to provide balanced power to the two propellers—Foss’s hybrid can use a single small engine to power the entire boat at low speeds. In fact, it can use any combination of its 4 engines to meet its power needs—or no engines at all, drawing power only from its battery pack.
This flexibility lets the tug tune its power output to the task at hand. Puttering around port, where speeds are typically limited to 6 knots (about 7 mph for you landlubbers out there), the hybrid tug can get by with a single engine, rather than the pair of behemoths that the typical tug requires. Pulling a big load, though, the tug can power up all 4 engines, and even store a bit of excess power in the batteries at the same time. The ability to match the engine to the power need lets the hybrid’s engines run much closer to peak efficiency than in a typical tug—simultaneously saving fuel and reducing harmful air emissions. Foss is still waiting for data to confirm the tug’s performance, but they expect fuel savings in the range of 20 to 30 percent.
At first, Foss thought that their tug would resemble the “Green Goat,” a hybrid locomotive that’s used in railroad switching yards. But the Green Goat uses a weighty battery array: a fine idea for locomotives, since more weight means more traction, but a no-no if you want a sailing vessel to stay afloat. So instead, to cut weight, Foss chose a smaller battery array for its tug. Hayman stressed that the hybrid tug’s efficiencies stem less from its battery storage than from the flexibility of its power management system. In fact, the software behind that system was the only truly novel bit of engineering that the tug required. (Balancing the power inputs and outputs is a tricky business, since—with 4 engines, plus a battery back that can be charging or discharging at any moment—the tug’s power system is quite a bit more complicated than that of a Prius.)
All in all, the hybrid tug is a nifty piece of work, and perhaps more importantly, a great demonstration that we don’t need major advances in technology to achieve significant energy savings. Sometimes using what we’ve already got—but in a smarter way—is all it takes.
I don’t mean to toot Foss’s horn too much here, but they’ve also received a grant to fit one of their plain-vanilla tugs as a test platform for new emissions control technologies—which holds the potential not only for emissions reductions from harbor tugs, but also leading the way for other sectors of the marine industry. Nifty!