Ah, the charms of San Francisco Bay: bright sun, glinting water, steady breeze, a trimaran and a simple wing. If you remember the last America’s Cup, you might picture high-adrenaline foiling at 40 knots. This is a different story. There’s no blistering speed, no grinding, no foils, no helmets or body armor, and no billionaire showmanship. This project isn’t about racing; it’s about practical, everyday sailing that reduces fuel use and emissions.
The vessel at the center of the experiment is Trillizas — Spanish for “triplets” — a Cross 42 trimaran that looks and feels like a mid-20th-century cruiser. Its single-element rigid wing is modest compared with the monstrous wings on America’s Cup cats: compact, almost quaint, and free-spinning on a vertical axis. The wing has no shrouds, stays or sheets. Even with the wing “engaged,” the little trimaran cruises around 7 knots under power. No one on board is manning winches; passengers might be more likely to reach for a sandwich than the helm.
Despite its unflashy appearance and sedate pace, the concept could be transformational. Wind-assisted motorsailing — not foiling at breakneck speed but steady propulsion assistance from a wing — could offer an economical, scalable way to cut fuel consumption on ferries and commuter vessels. That’s the central thesis behind Wind + Wing Technologies and the Trillizas test platform: demonstrate that wing-assist on working ferries makes both environmental and economic sense.
Ferries and excursion craft operating around San Francisco currently make a significant contribution to local emissions. According to the Bay Area Air Quality Management District, about 140 excursion vessels and ferries in the region generate hundreds of tons of CO2-equivalent emissions daily, along with particulate matter, nitrogen oxides and reactive organic gases. If wind-assisted ferries burn less diesel, they will emit less particulate pollution and fewer carcinogens — and, crucially, less CO2.
Cutting emissions is important, but operators are especially motivated by economics: fuel is a major operating cost. Many ferry operators are already investing in cleaner, more efficient propulsion systems to protect against diesel price spikes or future carbon rules, but those upgrades carry large capital costs. Wind energy, by contrast, is free at the point of use — and that potential for persistent fuel savings draws attention.
Trillizas serves as the prototype for these ideas. Owner Jay Gardner, who founded Wind + Wing and co-owns the Adventure Cat charter operation at Pier 39, converted the 9,000-pound trimaran from a cruising rig to an experimental platform fitted with a rigid wing that rotates freely and requires no trimming lines. The wing incorporates a counterweight, a small tail-mounted tab, an actuator and basic electronics to keep its angle to the wind within an efficient window. Project costs total about $355,000, covered by in-kind contributions from Photon Composites and Wind + Wing, plus cash from Adventure Cat, the Bay Area Air Quality Management District and the California Air Resources Board.
An all-star cast
Gardner commissioned naval architect Pete Melvin of Morrelli & Melvin to run a feasibility study after years of thinking about using wind energy to reduce ferry fuel use. Melvin’s calculations suggested energy savings on the order of 40 percent-plus for a suitably designed wind-assisted ferry. “The necessary technology is in place,” Melvin notes, particularly in wind-rich places like San Francisco Bay, where strong afternoon sea breezes are predictable.
Engineer Richard Jenkins designed and built the wing that now sits on Trillizas. Jenkins has experience with wings on fast vehicles — including record-setting sail-powered ground vehicles — and he emphasizes simplicity and reliability for ferry applications. The wing is almost entirely autonomous: it self-aligns to an optimum angle to the apparent wind and uses a simple tab actuator controlled by a sensor to return the wing to its preferred range when conditions change. When the wing isn’t wanted, such as during docking, the system can be disabled so the wing feathers into the wind.
The system was intentionally designed KISS-style — keep it simple — but it is far from unsophisticated. Each side of the wing carries a small solar panel that powers an inertial measurement unit, a control computer and the actuator assembly housed behind an accessible hatch. An encoder measures the wing’s angle relative to the vessel’s centerline. The goal is a durable, low-maintenance unit that can operate day after day on a working vessel without constant human intervention.
Learning from drones
Some of the wing’s design lessons come from autonomous marine drones. Jenkins’ work on long-range, ultra-low-power autonomous saildrones emphasized energy efficiency, robustness and redundant simplicity — traits that make sense on a ferry where a mechanical failure could be disruptive and costly. For initial trials, the wing is deliberately limited to about 60 percent of its theoretical maximum thrust to keep loads and complexity manageable and to favor longevity and low maintenance over peak efficiency.
On a test run across San Francisco Bay, Trillizas motored at a steady 7 knots with the wing engaged. Instant reductions appeared on the fuel-flow meter: fuel use dropped as low as 0.24 gallons per hour under a 17-knot true wind, which Gardner reports equates to roughly a 60 percent reduction in fuel burn rate under those conditions. Trillizas is a lightweight, low-drag cruising multihull, so the absolute numbers differ from what a heavier steel or aluminum ferry would see, but the trial proves the concept: a wing that favors apparent wind can deliver meaningful fuel savings when paired with engine-driven vessel speeds.
That potential has attracted attention from major operators. Jim Swindler, director of operations for Golden Gate Transportation’s ferry division — California’s largest operator — oversees a fleet carrying about 2.6 million passengers annually and spends roughly $6 million per year on fuel. A 40 percent cut in fuel consumption would translate into substantial savings and proportionally lower emissions. Swindler cautions that the technology still needs demonstration at scale: modifying or building a demonstration ferry and operating it on a scheduled route for a couple of years would be a significant investment and necessary next step.
Plans discussed include purpose-built catamarans around 149 passengers with electric, diesel-electric or cleaner diesel propulsion and tandem wings. But before committing to construction, independent analysis of the Trillizas trial data will be required to verify performance and economics.
Watching Trillizas glide past Alcatraz, wing quietly set against the breeze, it’s easy to imagine purpose-built, wing-assisted ferries crossing San Francisco Bay in the future. The idea combines mature aerodynamic and marine engineering with real-world economics: if the wings deliver reliable fuel savings and lower emissions, operators could deploy them at scale to reduce operating costs and environmental impact. As Melvin says, “Wouldn’t it be fantastic to come up with something that’s cost-effective and environmentally friendly?”
Indeed, it would — and the Trillizas trials are a practical step toward testing whether wing-assisted ferries can deliver both.
Dieter Loibner is sailing editor for Soundings.
July 2014 issue