Foiled in San Francisco
Putting a pair of advanced electric hydrofoils to the test. Well, one anyway.
In the eyes of this marine journalist, hydrofoils might draw a comparison to white whales. They’re not quite as rare as Moby Dick or Migaloo the white humpback, but from the perspective of linear time and probability, these boats are seldom spotted. They rear their heads briefly, yet submerge about as fast as they surface.
However, despite a spotty history that isn’t without incident, hydrofoils offer the promise of a chop-defeating ride and incredible efficiency. And some builders today believe they’ve corrected inherent flaws with stability and mastered the recipe. Electric hydrofoil builders Navier and Candela both invited me to test this claim. As chance would have it, I’d even be driving both company’s boats within 24 hours of each other. Navier, based in Alameda, California had just come out with their first running model, the 30, while Candela, located across San Francisco Bay from Navier in Sausalito, just released their second model, the C8, earlier this year.
I planned to write an unbiased firsthand account as to which vessel takes the edge as America’s hydrofoiling poster child, but unfortunately, things don’t always go as planned. I found out a few hours after arriving in San Francisco, that both Candela’s C8 and C7 ended up out of commission due to regularly scheduled maintenance gone awry. So, while I have no driving experience to offer on either of their models, in consolation, I did get to look under the hood, as much of the C8 had been dismantled for repairs. What follows is a glimpse into the technology powering both the Navier 30 and Candela C8, their differences, and thoughts on which one might hold the keys to the future of hydrofoiling.
The Core
When you look at a fully submerged, electric hydrofoil, what you’re really seeing is a waterbound cross between a drone and an airplane. At the core of these boats is the same computer programming used to stabilize just about every unmanned aerial vehicle (UAV) on the market. This comes as no surprise considering the chief engineers of both Navier and Candela previously worked designing flight programs for UAVs. In order for a fully submerged, wing-shaped hydrofoil to fly through the water and generate its characteristic lift with stability amidst the waves, the ability for foil positions to be instantly corrected is essential. Thus, the computers built into both the 30 and C8 enable flaps on the foils to adjust up to 50 times per second (Navier) and 100 times per second (Candela) to meet varying sea conditions at any given moment. That’s about five to ten times faster than a hummingbird (which flaps its wings 10 to 15 times per second). From an actuation perspective, the C8 is about twice as fast as the 30 but is that factor negligible or does it actually translate to real on the water results? That question remains to be answered.
“The flaps of the foils—our boat has three of them. They look like wings—they give the right amount of roll and pitch through the computer readings,” CTO of Navier, Kenny Jensen says. “The flaps create lift and roll by disrupting and deflecting the flow of the water at 50 flaps (actuating movements) per second,” he added, noting that the high-speed actuation of Navier’s flaps adds heavily to the safety of their boat.
Unlike a normal boat, which turns at the stern via rudder or outboard and pivots around a point near its midsection, hydrofoils bank like an airplane, tilting lift force to one side or another. Thus, an important safety feature that both companies have made sure to include is a series of sensors to keep track of the degree of the boat’s banking. The sharper the angle, the sharper the turn. But too sharp leads to danger. In past scenarios, turning hydrofoils have been known to capsize, most infamously in the 2013 Americas Cup training where the life of British sailing legend Andrew Simpson was lost. To prevent potential disaster, both Navier and Candela’s boats are designed to bank no greater than 30 degrees. Should the captain try to turn tighter than that, or at 30 degrees for longer than a moment on the C8, the engine’s RPMs will drop. (The 30 actually maintains speed throughout a 30-degree bank, which might indicate the C8 is capable of sharper turns, but this is yet to be determined.)
“The whole idea with that is that basically, if you want to turn sharper, you can reduce the RPM and then that will reduce your turning radius so you turn sharper, but you won’t actually bank more. You will just have a smaller turning radius,” Candela’s Chief Control Systems Engineer Kristian Lauszus explains. “Your turning radius is basically given by your speed forward and then your rotational speed around the C-axis. So since I cannot adjust your rudder, [instead] I can know the speed to make the turning radius smaller.”
Lauszus further explains that theoretically you could set no limit on degree of turn capable by the C8, but the Candela team decided that the safest degree was 30. If the boat hit a big wave, it could go from being 30 degrees to minus 30 fairly quickly, although that scenario would have to be extreme.
“In practice you never really need to bank more than 30 degrees, you can make really tight maneuvers at 30 and if you really want you can always land [the boat], turn around and take off again really quickly,” Lauszus says, adding that it’s not possible for the C8 to actually capsize and remain overturned. “When you design a boat, you need to do a stability analysis on it, so even if you place it at 90 degrees it should always go back upright.” There are, he adds, over a thousand different safety mechanisms in place, checking all kinds of things, like angle of attack, pitch, roll, yaw—the list goes on.
When it comes to safety, Navier and Candela’s offerings share many similarities, but where foil and engine design are concerned, there are quite a few contrasts. Candela’s C8 foil is built with two flaps; one at the end of two mid-hull struts that run across from port to starboard, and one at the stern, along a single pod (called the C-POD) that, as Lauszus notes, houses two electric engines with a combined power of 100 kilowatts. In contrast, Navier’s 30 has three flaps; one flap mid-hull, and one at the base of each motor. Along with two separate props, the 30 has two separate, independently operable 90-kW engines. It’s a setup that makes for superior docking ability—which I’d put to the test.
I can’t personally attest to the differences two flaps make over three, nor to the difference between two independently-operating engine units versus one dual-engined pod, as I only managed to drive the Navier 30, but we can certainly look at range claims. When it comes to the longest electric boat range, Navier’s 30 holds the belt, pulling 65 nautical miles per charge at cruise, whereas the C8, manages 57.
Testing the Navier 30
Built by famed Maine boatbuilder and tech company Lyman-Morse, Navier’s carbon-fiber 30 has a sleek, black angular exterior that feels more reminiscent of Darth Vader’s Executor than your average boat.
In the spirit of safety, Sam Seder, the head of operations at Navier showed me a video of the 30 driving straight through 60 mile-per-hour winds and up to six-foot chop the way a skiff might coast through the harbor on a perfectly calm day. The stability and performance capability of the 30 largely results from the efforts of the boat’s naval architect Paul Bieker, Oracle Team USA’s principal engineer for the 35th America’s Cup and a man with next level expertise in hydrofoils.
The Navier’s “canard” foil arrangement positions the foils forward and aft in the boat where they can be lifted above the water when the boat is not in use. Thus, fouling while the boat is left at the dock can be avoided.
“It took me a while to settle on the Navier 30 foil configuration,” Bieker says. “It has a number of big advantages over other foil configurations. The canard foil configuration almost doubles the distance between the forward and aft foils and this improves its pitch stability and ride quality relative to a conventional (airplane style) foil arrangement.”
Foil surface smoothness is also critical for hydrofoiling performance, Bieker notes. Candela’s C8 also has a means to avoid foil fouling, with its foil struts able to retract out of the water, putting the boat into a “harbor mode.” The C8 also has a planing mode, where its prop shortens to a 40-centimeter draft, and the foils remain retracted, allowing boaters to drive in shallow water.
Walking me around the 30 that the Navier team had stashed in their warehouse, Seder went on to explain how its engines are engineered to operate independently of each other. “We build everything in double redundancy, so that no matter what happens you can get home,” Seder says.
Soon we took our leave from the nearby docks and I got to experience firsthand how the Navier’s dual electric engines made for easy docking. There are no bow thrusters but the 30 puts its engines to the task ably via a joystick next to the throttle, which allows for remarkable, near silent maneuverability. Like a nine-year-old at an arcade playing Tetris, I even made a joystick-controlled 360 or two around the docks just for the fun of it. According to Bieker, the most efficient configuration for a canard is a one-piece aft foil a la Candela’s C8, but by splitting the aft foils into two independently controllable units—as Navier’s 30 is designed—the boat gains amazing low-speed handling characteristics.
Out past the marina, the 30 got up to speed quickly and at around 15 knots we lifted up and suddenly, we were flying. Due to the precaution of handling a brand new engine, Seder only let me test the top speed for brief moments, but when I opened her up, the 30 reached just past 35 knots. According to the Navier team, she cruises at 20 knots while Candela’s C8 tops out at around 27 knots while cruising around 22.
Experiencing Candela’s C8
Again, I never had the chance to test the C8 on the water, but I did observe the mechanical team over at their boatyard wrenching on a bare, parts-stripped model I had originally intended to test. If I didn’t get to drive her, I did at least have the chance to look her over more closely.
Candela’s C-POD propulsion system resembles a small torpedo at the end of a shaft and houses two motors that power a pair of very small in-line props. Each motor directly drives a propeller to minimize friction loss and the propellers contra rotate which, according to the Candela team, adds 15 percent more efficiency to their thrust over a single, spinning prop. Another plus to the C8’s motors is that they come with a maintenance-free operating period of over 3,000 hours of driving, however considering the necessity of special tools, the only places to have a Candela worked on will be Candela facilities, that perk ends up a bit muted.
When retracting the foils on the C8, the support struts actually rise up from either side of the dashboard. It’s an improvement from the mid-deck retraction of the C7’s struts, but still feels intrusive.
Abovedecks, while most the surface area bore an accumulation of tools and laboring European mechanics, I did notice the bucket seats Candela has developed in partnership with automaker Polestar. With a thick, firm feel, they were lacking in plush comfort, but in their favor, they certainly seem weather durable and are very light—only eight pounds each including their carbon fiber frames.
One standout feature that Candela offers is its user interface. All settings on the boat, from turning on the cooler to navigation or assessing the boat’s battery life can all be done from the 15-inch control screen, but you can also track your navigation and the boat’s vitals right from an app on your smart phone.
For either of these electric foiling innovators, a successful future seems heavily dependent on an increase in charging port options available at local docks, and both companies are in talks with the city of San Francisco to grow and improve such amenities. According to Seder, at least ten level three (fast) chargers—the kind that will let their boat be fully charged in less than an hour—will be added to marinas in the area by the end of 2024.
After all was said and done from this tech journey, I return to Southern California with some humble parting thoughts, for what they’re worth. Both boats are clearly innovative, but the struts that pop up out of the C8 are cumbersome and an eye sore, and it’s tough to beat the added perk of maneuverability that the Navier 30 wields due to its twin independent engine system, along with its edge in distance. Plus, I actually got to take the Navier for a spin. If I’m playing referee, I’d raise Navier’s glove for this first round.
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This article originally appeared in the August 2023 issue of Power & Motoryacht magazine.
Source: https://www.powerandmotoryacht.com/boats/foiled-in-san-francisco
