On a fishing trip out of Miami some years back, our 30-foot center console was pounding through a hard 2-foot chop when the captain turned and said, “One of these days, we need to get all this paved.”
In the time since, no one has figured out how to make open water as smooth as a newly opened jar of peanut butter, but some boatbuilders are touting what they call the next best option: flying above the waves.
The trick relies on hydrofoils, basically underwater wings, that lift the hull out of the water and allow the boat to glide above the slop. As a bonus, foils make a craft more efficient and more environmentally friendly. The technology has been around in theory and practice for more than a century, but certain drawbacks (real and perceived) have prevented foiling from taking hold beyond the world of high-speed ferries.
The latest attempt to bring foils to mainstream boating came from what may seem like a counterintuitive place: sailboats, which don’t typically bring to mind thoughts of speed and efficiency. Unless you’re talking about the America’s Cup. Team New Zealand hit 40 knots in a 17-knot breeze during Cup racing in 2013. That’s speed and efficiency.
It’s taken awhile, but the innovations of Cup sailors have begun to trickle down. A few new companies and even an established brand or two have started to sell foiling powerboats. Each has certain common elements, but their vast differences also suggest how much builders still have to learn about the range of possibilities.
According to their builders, some of these boats can make running through seas up to 4 feet feel more like a hayride than a tumble down the side of a rocky hill in a wooden barrel. And the boats reportedly can increase efficiency by 30 to 60 percent — a potential breakthrough for electric power.
“As soon as you try it, it’s like another world,” says Alois Vieujot, manager at Enata Marine in Dubai, United Arab Emirates. Enata’s $900,000, 35-foot foiling vessel is powered by a pair of turbo diesels and is capable of hitting 40 knots. “Afterward it doesn’t make sense to own anything but a foiler. That would be like going back to coach after you’ve gotten used to flying first class.”
How it Works
Foils generally come in two varieties: V-shaped, surface-piercing blades, and T-shaped blades that remain below the water. Some builders us a combination of both. Similar to wings on a plane (known as airfoils), the shape of a hydrofoil forces more water under the blade than over it, creating a disturbed pattern on the higher side and more pressure on the lower side. That generates lift. The more water that passes over the blade, the more lift is generated, so as a boat gains speed, the hull lifts out of the water. Designers adjust the size and shape of the blades, as well as their angle, so that at some point, the weight of the boat and the lifting forces balance, allowing the boat to settle at a steady height above the water.
In most applications, the boat has to reach 15 to 18 knots before it rises. At lower speeds, the foils are retracted, and the vessel operates as it normally would (including having the ability to sit on a trailer). As the boat gains speed, a push of a button extends the foils, and the hull takes off.
“Once the hull lifts, you don’t have all that drag of pushing the hull through the water,” Vieujot says. “Only the surface area of the foils touches.”
SEAir, a French company that works with boatbuilders to customize its surface-piercing foiling system to their hulls, did side-by-side tests of 32-foot RIBs with twin 200-hp outboards. At 4,000 rpm, the standard hull ran at 24 knots, burning 0.42 gallons per nautical mile. At the same rpm, the foiling RIB cruised along at 31 knots while burning 0.26 gallons per nautical mile — a 29 percent speed gain combined with a fuel efficiency increase of 37 percent. “In certain sea conditions, we have seen fuel-consumption gains of 40 to 50 percent,” says Christine Perrot Cornu, SEAir’s head of business development.
At the other end of the spectrum is the Princess R35, a cruiser with two T-shaped foils near the transom. They don’t lift the hull completely out of the water, but they improve efficiency by 30 percent at cruising speed, according to the company. At the boat’s top speed of 50 knots, the speed and efficiency even out with a standard hull because “at that point it’s just about engine power and brute force,” says Princess COO Paul Mackenzie.
The company developed the foils because it wanted a 35-foot, entry-level model that offered something different in the class. Mackenzie and crew didn’t think the Princess buyer was ready for full foiling, but he doesn’t rule it out for the future. “Innovation is slow in boats, but I think in the next five to 10 years we will see it more and more,” he says, adding that Princess is already experimenting with foils on vessels up to 100 feet.
In addition to the improved efficiency, foiling boats leave almost no wake, which reduces shoreline erosion and disruption of fragile habitats. And because they don’t pound, they’re quieter than many other boats.
Then there’s the feeling of riding aboard them.
“It really is like flying,” says Mikael Mahlberg, communications director of Candela Boats in Sweden, which brings together foiling and electric power. The company says that with a 40-kW electric motor, its 25-footer has a top speed of 30 knots and a range of 50 nautical miles at 22 knots. “If you want to go far and fast with a battery, foiling is the only way,” he says.
Mahlberg adds that on board, guests will feel a “light slamming” only after seas reach a height of about 5 feet. This claim tracks with information from other foil makers who say their boats can smooth chop from about 2 to 4 feet, and after that point can offer a cushier ride than a conventional hull. “The foils act as a sort of suspension system,” Perrot Cornu says. “The boat comes down softly.”
Vieujot says the test team at Enata has pushed its 35-footer hard enough that the front foils have come completely out of the water. “It lands fine, smooth,” he says. “But it makes a big splash. You will get wet, but otherwise you’ll hardly feel it.”
The price, typically, of a smooth ride has been awkward turns, since boats with foils generally stay flat through curves. For anyone used to the banking performance of a typical monohull, a flat turn can be unsettling at the least and, some argue, dangerous at the worst. To account for that problem, modern foil builders have created dynamic systems in which dozens of sensors measure speed, angle and distance to the water, among other parameters, and automatically adjust the foils so the boat banks into curves and maintains an optimal attitude while running straight ahead.
“There’s a lot of software,” says Mahlberg, whose boat has sensors that fire about 100 times per second. “There’s about 90,000 lines of code in there.”
Such systems also allow for complete touch-screen control, automatic updates, troubleshooting and, in some cases, remote mobile-device control.
High and Dry
Other knocks on foiling boats include cost and the fear of striking objects in the water with the foils. Today’s builders utilize high-strength carbon fiber to make their foils, meaning they can withstand high impact, but they’ve also designed breakaway points, much like those on an outdrive, so that a big enough collision will cause the foil to tear away without damaging the hull.
Additionally, the foils are usually mounted in sea boxes as an added layer of protection, and the systems have been tested to ensure that a lost foil will result in a safe landing back on the water. As far as hitting sea animals, in no-wake or speed-controlled areas where aquatic life is known to proliferate, the boats wouldn’t be foiling anyway. And, builders say, if a skipper hits a whale or manatee at high speed on the open water, the crash is going to be problematic no matter what type of boat he’s driving.
Costs for foiling boats, builders acknowledge, are higher than for traditional boats, often as a result of research and development, design and materials for the foils. Even so, Princess and Enata clients generally don’t get sticker shock. Mahlberg says that while Candela’s builds may be more expensive than comparable planing-hull options, they’re less expensive than similar electric-powered boats.
Perrot Cornu says buyers see savings by getting similar performance with a smaller engine — say, a 90-hp outboard instead of a 115. And there’s the fuel consumption, too. “When we sit down and work out the numbers,” she says, “depending on how much they use their boat, we often find that the boat pays back the difference in three years.”
That doesn’t seem like too long a time compared to the century that foiling boats have been sitting around, waiting to reach the mainstream. Maybe their time has come.
“Big, epoch-changing developments don’t happen often in boating,” Mahlberg says, “but I think there will be big investments in foiling because it works.”
Length: 35 feet, 9 inches
Power: twin V-8 gas
Performance: 50-knot top speed; 30 percent more efficient at cruise than a traditional hull
Model: The Foiler
Length: 32 feet, 2 inches
Power: twin V-8 turbo diesels
Performance: 40-knot top speed; 40 to 50 percent more efficient at cruise than a traditional hull
Model: Flying Tender, Flying Boat (various builders, including Beneteau and Zodiac)
Length: 17, 22, 25, 32 feet
Performance: 30 to 50 percent more efficient than a traditional hull
Model: The Seven
Length: 25 feet, 3 inches
Power: 40-kW electric outboard
Performance: 30-knot top speed; 50-nm range at 22 knots
This article was originally published in the September 2020 issue.