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Hydrofoils for Sailboats

• By By Steven Callahan
• Updated: July 29, 2020

Hydrofoils have been providing dynamic lift since fish sprouted fins. And people have been employing foils ever since they first put paddle to water, and certainly since adding keels and rudders to boats. But the modern, flying America’s Cup boats, kiteboards, Moth dinghies, shorthanded offshore thoroughbreds—these are all ­playing in a new world in which the terms “hydrofoils” or “lifting foils” describe those oriented to raise a hull or hulls from the water. In these racing realms, if you ain’t got foils, you ain’t got nothin’.

Lifting foils that allow these boats to sometimes home in on three times the wind speed might appear to be of little interest to cruising sailors, but with such common cruising features as self-steering and autopilots, self-tailing winches, rope clutches, fin keels and faster hull shapes all having been passed down from the racing scene, one must ask, “What promise, if any, do hydrofoils hold?”

Lifted or partially lifted boat patents extend back to 1869, but workable watercraft took roots along with early flight. Italian Enrico Forlanini began experimenting with foils in 1898. In 1906, his 1-ton 60 hp foiler reached 42.5 mph. Alexander Graham Bell’s HD-4 Hydrodrome flew on Bras d’ Or Lake at 70 mph in 1919. And several sailing foiler patents began appearing in the 1950s. Notably, JG Baker’s 26-foot monohull, Monitor, flew at 30-plus mph in 1955. Baker experimented with a number of foil configurations, and at least built, if not used, the first wing mast. The first offshore foiler was likely David Keiper’s flying trimaran, Williwaw , in which he crisscrossed the Pacific in the 1960s.

By the 1980s, numerous speed-trial and foil-enhanced offshore-racing multihulls showed huge promise, and have since evolved into behemoth trimarans clocking 30 to 40 knots continuously for long periods, not to mention the monohulls in the Vendée Globe (and soon the Ocean Race) that are capable of speeds exceeding 30 knots. But as boat designer Rodger Martin once reminded me, “If you want a new idea, look in an old book.” He was right. The fully foiling monohulls that will compete in the 2021 America’s Cup will bring things back full circle to the foiling monohull Monitor .

Fluid Dynamics Primer

Any foil—a wing, sail, keel, rudder or lifting foil—redirects the flow of fluid (air included), creating high- and low-pressure areas on opposite sides of the appendage, while developing lift perpendicular to the foil’s surface.

Advancements in foiling science is due in part to the hundreds of foil shapes that were tested, with tabulated results, by the National Advisory Committee for Aeronautics, the forerunner of the National Aeronautics and Space Administration. For the better part of a century now, aircraft and boat designers have been able to choose from a spectrum of refined foil sections that produce predictable amounts of lift and drag for known speeds of fluid and angles of attack, or the angle at which the foil passes through the fluid. Sections of efficient faster foils, as seen on jets or as we flatten our sails to go upwind or reach high speeds, have smaller nose radii and are thinner, with the thickest section of the foils farther aft, up to nearly halfway toward the trailing edge.

The most efficient foil sections at slow speeds are fatter, with the maximum thickness farther forward, and with larger nose radii, than faster foils. The angle to fluid flow or angle of attack also is greater. We see these slower foils on wings of prop planes and sails when off the wind or in light conditions.

Most sailors are familiar with traditional foils on boats, the teardrop sections of keels that produce lift to weather, reducing leeway, and of rudders, allowing them to steer. Even a flat plate can be a foil, but these tend to be inefficient. Such a shape is prone to fluid separation from the surface, meaning they stall easily, and they maintain poor lift-to-drag ratios. Even keels and rudders are somewhat lift-­compromised because they are ­symmetrical and have to work with fluid coming from either side, whereas lifting foils are more like aircraft wings or propellers, with asymmetrical sections honed for performance in a more stable, fluid flow.

The point is, any foil can be employed at various angles to the surface to prevent leeway, produce increased stability, or help lift the boat out of the water. But those not required to work with fluid flowing from opposite sides can then be honed to maximize lift and minimize drag. Asymmetrical foils were used on boats like Bruce King’s bilgeboarders, including Hawkeye , back in the 1970s. And, designers, including Olin Stephens, had previously employed trim tabs behind keels to improve keel performance.

Sails, which are heeled airfoils, not only drive the boat forward, but they also produce downforce, actually increasing the dynamic displacement of the boat. To counter this and keep the boat sailing more upright, multihull designer Dick Newick first employed slanted asymmetrical hydrofoils in the outer hulls of his small charter trimaran, Lark , in 1962. A portion of the lift developed by the hydrofoil resisted leeway, while a portion worked to actually lift the leeward hull, keeping the boat more upright and reducing dynamic displacement and drag.

Anyone who has ridden on even a foil-stabilized boat will know how riding at least lightly on the waves, and especially above them, beats smashing through them. When boats lift off, everything gets a lot smoother, drag falls away, and the boat accelerates.

Cruising on Foils

But why would a cruiser want to whip over the sea? Wouldn’t this demand an inordinate amount of attention by the crew? Would lifting foils even be applicable to a boat that must have substantial displacement to carry crew and stores? Aren’t cruising-boat hydrofoils an oxymoron?

Maybe, but I believe our boats’ hulls are likely to sprout fins much as fish have as we orient foils to more efficiently resist leeway, add stability, aid steering, reduce drag, increase comfort, allow for shallower draft, and enhance wider ­variations in hull shapes.

Boats have gotten increasingly wide through the years to advance form stability, improve performance (primarily off the wind), and boost interior volume. But the downside is that fat boats tend to slam more upwind. What if you could reduce dynamic displacement of the boat and lift that hull even partially from the water? The result would be less slamming, especially upwind.

At the same time, what about narrower boats that are known for being more seakindly, especially when closehauled, but lack form stability to carry adequate sail area for powering upwind, and tend to roll badly downwind? Or shallow-draft vessels that are lovely for cruising, but again, tend to suffer from reduced stability? Foils can give that stability back.

Looking ahead, boat ­designers might choose to reduce ballast, making up for it with a foil. In short, lifting foils can reduce boat drag and motion while increasing power and performance.

Pitching also does no favors for speed or crew comfort. Foils can come into play here as well. Foils parallel to the sea’s surface resist motion up and down, and a lifted boat skating above chop also is less prone to hobby-horsing through waves. Multihulls have always been particularly susceptible to pitching for a number of reasons, but watching videos of multihulls sailing to weather show an obvious huge advantage that foilers have compared with nonfoilers. Offshore multihulls now routinely employ T-foils on the rudders to control the fore and aft angles of the boat (attitude), a feature easily adaptable to any vessel.

OK, so what’s the cost? Obviously, the more things sticking through the hull, ­especially if they are retractable, the more it’s going to impact the interior. There would be added weight, complexity and cost. Foils also create noise, and there’s susceptibility to damage from hitting stuff. And let’s not forget compromises with shapes, purposes and things not yet imagined.

As for damage, it’s possible to fold the foils back into the hull. Think swinging center- boards or actual fish fins. Daggerboardlike foils can at least employ shock-absorbing systems similar to the daggerboard arrangements found in many multihulls. This includes weak links that are outside the hull, so if a foil is struck, it frees the foil to fold back or to come off before being destroyed or damaging the hull. Or, foils might hang from the deck rather than penetrating the hull, allowing them to kick up (and to be retrofitted to existing boats). These configurations also relieve the interior of intrusions, and keep the noise more removed from it. I have no doubt that numerous talented designers will be exploring all kinds of options and compromises in coming years, finding ways to make foils both practical and more than worth the compromises.

Sailing more upright, ­shallower draft, speed, ­comfort—what’s not to like? Just what is possible? I have a feeling the cruising community is about to find out.

Steven Callahan is a multihull aficionado, boat designer and the author of Adrift , an account of his 76 days spent in a life raft across the Atlantic.

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Sailing’s Hydrofoiling Revolution

• By Herb McCormick
• January 18, 2023

There’s a revolution underway in the sport of sailing, and it can be summed up in one simple word: foiling.

More specifically, we’re talking about hydrofoils , the winglike appendages mounted beneath the hull of a vessel that, at a certain speed, lift the hull clear of the water. When this happens, the foiling sailboats can reach speeds two or even three times faster than possible in “displacement” mode.

And sailboats are just one element of the foiling revolution: Surfboards, paddleboards and powerboats are also getting in on the act.

An Italian naval architect named Enrico Forlanini is credited with developing the first waterborne hydrofoils, which he affixed to a 60 hp, airscrew-driven craft that topped off at 36.9 knots back in 1906. In the century that followed, a series of would-be inventors took a swing at the concept with varying degrees of success. Foiling sailboats finally ascended into the mainstream during the 2013 America’s Cup, when Oracle Team USA beat Emirates Team New Zealand in a match between foiling 72-foot catamarans (the Cup has been contested in foiling cats ever since).

Surprisingly enough, my first foiling experience happened some three decades ago, aboard something called a Hobie TriFoiler, from the popular manufacturer of Hobie surfboards, beach cats and kayaks. The TriFoiler, basically a 22-foot trimaran with a central pod and a pair of mainsails stepped on the twin outriggers, was invented by a fanatical California engineer named Greg Ketterman. The sail controls were laid out just forward of the tiny airplane-style cockpit; you steered with foot pedals. It was so ridiculously easy that even a gremmie like me had the thing foiling within moments of getting in and reaching off.

But after the initial thrill, it was actually kind of boring. Which, I believe, is why it went out of production soon after. The TriFoiler was, unfortunately, way ahead of its time.

Such was the extent of my personal foiling experience until this past summer, when a new class of foiling monohull skiffs called Persico 69Fs rolled into my home waters for a series of races among youth squads in the class’s inaugural season. I got an invitation to take a spin.

After donning my helmet, wetsuit and life jacket, I was handed the helm with a pair of skilled young sailors on board. At 25 knots, we were towed into Narragansett Bay behind a powerful RIB, foiling all the way. It was terrifying. And a preview of coming attractions.

Once the tow dropped us, the sails went up and we bore off. I skied the tiller extension while scrambling out onto the hiking racks. Which sent us off on a screaming reach. Which flipped the 22-foot-7-inch carbon rocket ship.

Twenty seconds into foiling, and I’d capsized the bloody thing. How embarrassing.

The kids, bless them, were kind and patient. We got the whole shooting match, including ourselves, back upright and tried again. The mainsail trimmer sheeted it home, we started to accelerate, and he said: “Here we go! You’re up. You’re flying!” Indeed, we were.

Hard on the breeze in the 12-knot southwesterly, things unfolded quickly. Spray was flying, and I took more than one solid wave to the kisser. I was mostly too frightened to concentrate on anything but driving, but I did glance at the speedo once: 17.4 knots. (I felt pretty chuffed until later learning a 69F’s top speed is 34 knots. Ugh.)

However, I guess I’d proved the point: With a couple of sailors who know what they’re doing, foiling is for everyone. From now on, just call me Mr. Foiler.

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Foiling and Hydrofoiling: Everything you need to know

A foiling International Moth dinghy. Photo: Christopher Ison / Alamy

What is foiling?

Although foiling or hydrofoiling feels like a recent revolution to take the world of watersports by storm, it is actually much older than many appreciate.

In terms of motorised waterborne craft, the first foiler was a motorboat designed and built by Italian inventor Enrico Forlanini in 1906.

It did, however, take quite a bit of time before foiling boats with sails took to the water, but even then many people might be surprised to learn that even in the 1970’s the foiling trimaran, Williwaw, covered over 20,000 sea miles in and around the South Pacific all on its foils.

It turns out the history of hyrofoiling goes back further than many think.

It was not until the early-2000s that foiling really started to take hold, with a  development dinghy class, the International Moth, leading the way.

Foiling boats

With huge amounts of interest in the 11ft Moth dinghy, foiling began to spread throughout the sport of sailing. And it was not long until hydrofoiling boats of all different shapes and sizes were taking the water.

Over time, some traditional classes converted to foiling – the A-Class and C-Class catamarans being examples. But more new boats were also designed specifically with hydrofoiling in mind.

In 2013 Emirates Team New Zealand built their 72ft America’s Cup catamaran to be a foiler, forcing their competition for the Cup, Oracle Team USA to convert their AC72 into a foiler to stay competitive – ultimately Oracle Team USA won the Cup in one of the biggest sporting comebacks of all time .

To date the America’s Cup has not looked back with the competition taking place in smaller hydrofoiling AC50 catamarans in 2017 and the newly conceived monohull foilers, the AC75 s, in 2021.

In 2021 the Olympics Games introduced the first ever foiling catamaran in the Nacra 17.

Foiling yachts

Offhsore, 90ft Ultime multihulls on their foils are competing to be the fastest to race around the globe and design houses across the globe are racing to create foiling yachts for the masses which could dramatically reduce cruising times from one destination to the other.

There are also many classes of yacht that are taking some of the lessons from fully foiling craft and putting them to use in a semi-foiling manner.

Here the biggest technical innovation is in the IMOCA60 class, which is famously used for the single handed non-stop round the world race, the Vendée Globe .

The latest couple of generations of IMOCA 60s have been build with huge, technologically complex foils to generate lift. These are powerful enough to lif the boats fully out of the water, but as yet the class rules do not allow for rudder foils which would stabilise flight and allow for full foiling.

Where sailing boats and yachts have, arguably led the way in the history of foiling over the past decade or so this has filtered down into a plethora of other watersports craft.

Although in the early days foiling was typically the preserve of elite sailors and watersports professionals, increasingly we have seen boats and boards designed to foil in the hands of the average sailor, surfer or windsurfer.

This race to bring the fun of foiling to beginners is continuing apace with beginner foiling boats, windsurfers, surfers etc. coming to the market every year.

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“iFLY15 is the unique combination of high performance with easy accessibility – for maximum performance and maximum fun.”

Cec catamarans -ifly15 team, “we love speed while keeping control – high speed needs to be controllable. the flying boat of the future, is a stable foiling sport catamaran.”, cec catamarans – ifly15 team, „ foiling: one of the things you have to experience to really feel it. “, jimmy spithill, skipper oracle team usa, “stable flight is the key to high performance sailing”, “ifly15 – get the balance right between a nice sporting challenge and a reasonable and controllable level – enjoy the exhilaration, the speed and the adrenaline in your veins, but always stay master of the situation “, “stable flight attitude is the most important prerequisite for high performance sailing.”, victor diaz de leon, sailgp team usa, “stable flight attitude is key for easy foiling. ifly15 with superior flight stability delivers immediate flying fun within the first minutes. advantage through high-tech.”, “the ifly15 is the quickest boat around the course, … “, arno terra – sailor, ifly 15 one design and ifly razzor pro, the  performance  foiling  catamaran, for maximum speed and maximum control.

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The quality and performance have been proven for 8 years and further developed to maximum perfection in every detail

IFLY HYDROFOIL SAILING – EXCELLENCE, FIELD PROVEN TO PERFECTION

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Stay tuned for foiling events and specials!

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The most innovative development in foiling technology

About ifly15, stable flight  is  key for both: first for highest performance and foiling in a wide wind range, including rough and wavy conditions, but also easy access into foiling…...

iFLY stands for uniqueness in design and function. Its superior Flysafe ® active foil control system autonomously supports the stable horizontal flight position in the longitudinal and lateral direction. The 4 T-Foils do not have to be operated by the sailor during sailing.

Average skilled dinghy or catamaran sailors with some trapeze experience can safely foil with the iFLY15 after only a few hours. Quick access – the immediate sensation of success – steep learning curve. In the hand of an experienced sailor, iFLY15 offers a whole new sailing experience with previously not experienced speeds and agile maneuverability.

The flight control system, combined with numerous fine-tuned innovations , ensures safe foiling even in strong winds and rough seas.. Stable flight attitude allows pushing hard, so in good conditions, iFLY reaches high boat speed beyond 30 knots in a controllable way.

IFLY15 offers freedom to fly alone or in pairs. Due to the exclusive use of high-tech materials , iFLY15 is extremely rigid and weighs less than 90 kilos ready to sail. With its low weight and its state-of-the-art hydrofoils, it is airborne in winds as low as 2Bft. / 6 Knots.

iFLY15 has a length of only 15 feet, is easy to transport, quick to get ready to sail, and can be easily slipped from the beach using a conventional beach trolley.

Its sophisticated design reflects the highest demands on quality and function.

iFLY15 – customer reviews

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VERY STABLE, EXTRAORDINARY STABLE. IT IS EXTREMELY INTERESTING, BECAUSE YOU IMMEDIATELY SEE THE ACCESSIBILITY OF THE BOAT.

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IFLY RAZZOR PRO – THE NEW IFLY FOR EXPERIENCED SAILORS

THE SINCE 7 YEARS PROVEN IFLY15 WITH FLYSAFE® DYNMAMIC FOIL CONTROL has now a pur Racing fellow: THE iFLY RAZZOR Pro. THE iFLY racing VERSION ENABLES EVEN HIGHER PERFORMANCE, to sail in extremely tough conditions and allows sailing with XXL rigs. THE MAIN DIFFERENCE BETWEEN THE IFLY15 ONE DESIGN AND THE IFLY RAZZOR PRO IS A BIGGER RACING RIG, SPECIAL FOILS AND THE MAIN FOIL DIFFERENTIAL (MDT), WHICH IS MANUALLY TRIMMED BY THE SAILOR. THE MDT IS WORKING HAND IN HAND WITH THE FLYSAFE® DYNAMIC FOIL CONTROL SYSTEM.

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ROUND TEXEL RACE 2024

“We’re taking off! Foiling is THE Watersports Trend! – „Boot International 2024“ in Düsseldorf / Germany once again showcases: Foiling is THE trend in watersports.

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THE FLYING YACHT The new era of sailing begins

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Technology : "There is no such thing as the perfect foil" - how airfoils work

Andreas Fritsch

 ·  25.02.2024

YACHT: The SailGP regatta series recently tested new foils and reported an incredible 15 per cent jump in performance. That seems astonishing, as at the top end of the sport there is often a fight for every tenth of a knot. Is the foil technique still in its infancy so that such huge leaps are possible?

Martin Fischer: 15 per cent is definitely possible. However, they have tested a different configuration, so far these are so-called J-foils, i.e. bent inwards. When the boat is placed on the foil, the vertical lift of the wing, the centre of lift, is inside the hull. So you have a certain righting moment. And this is determined by how far apart the centre of gravity of the boat and the centre of buoyancy of the foil are in a lateral direction. However, the new profiles are T-foils, which are bent slightly outwards. This shifts the centre of lift of the wing outwards and the righting moment increases significantly, allowing more pressure to be applied to the sail. This means that 15 per cent more performance is possible.

If you had stayed with the J-Foil, would there not have been this significant increase?

Exactly. They haven't found a particularly clever new shape that has so much less resistance, but simply increased the power of the boat by ten to 15 per cent. It's as if you were to install an engine with 50 hp more in an existing car.

According to SailGP, the cavitation limit has also been moved upwards by six knots and they now hope to reach 59 knots. Until now, many teams, such as the Imocas or Ultims, have said that above 50 knots is a kind of sound barrier for cavitation ...

In principle, this limit already exists. With a conventional foil, there is one side that has positive pressure and the other has negative pressure. At higher speeds, the negative pressure becomes so great that the vapour pressure of the water is undercut and it evaporates directly on the surface of the profile. This means that part of the foil is no longer working in liquid water, but in water vapour. This leads to a bubble wake, which drastically increases the drag. And if this happens on large parts of the wing, you can no longer go much faster. Typically, once cavitation has started, you can still achieve two or three knots more, but after that it's over. However, it is possible to build foils that only start to cavitate at 60 knots. But then they are pretty bad at lower speeds. An example: If we have a foil that kavits at 40 knots and one that kavits at 50, the one that starts at 40 is faster in the range between zero and 40 knots. And the other foil is then only between 40 and 50 knots faster. So that would be good in a lot of wind downwind, but on all other courses and in less wind the boat would be slower.

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It doesn't matter in the SailGP, these are standardised class boats, they all use the same foil and the race committee decides which one to use. But in the America's Cup, the Imocas or Ultims, the choice is up to the team. In the open classes, you have to think carefully about when cavitation is allowed to start. It is an active design decision.

Different working states of a foil

So the idea of the border is basically wrong?

Yes and no. You can have cavitation even at ten knots. It just depends on the negative pressure of the airfoil. Let's take the Imoca foils: they cavitate at around 35 knots. This is done on purpose because an Open 60 doesn't sail any faster, it doesn't fly completely. That's why it makes no sense to use profiles that only kavit at 40 knots, but would be slower from zero to 33. But there is an upper limit. Beyond 60 knots, it becomes difficult not to kavit with a foil designed for use in liquid water. In addition to the high-speed aspect, there is also a cavitation problem at low speeds. If the foil is still to achieve sufficient lift, you have to work with a high angle of attack. Then, even at low speed, you have negative pressure peaks that cause the profile to cavitate locally at the top front even at low speed, which slows you down again.

The difficulty for foils in the America's Cup or SailGP is that with conventional profiles you can cover a speed range of 20 to 25 knots in which the foil does not cavitate at all. And you have to choose this range consciously, and it is difficult to increase. If you want to take off at 20 knots, your speed range without cavitation is 20 to 40 knots. If you want to reach 45 knots, the take-off speed is 25 knots.

Is it ideal to build as many foil sets as possible?

Actually yes, but in the America's Cup it's forbidden, we're only allowed to use one set of foils. This was done on purpose to keep the costs within reasonable limits, because they are extremely high. SailGP uses more profiles because of the different venues with very different wind conditions, so that the boats fly even in light winds.

How much does a set of foils for an AC boat cost?

One is well over a million euros, and with a reserve foil that's three to three and a half million euros. We didn't want teams to develop extreme profiles that could then lead to very large differences in speed. In that case, it becomes a game of poker: Which foil do I use in which wind? If you get it wrong, it's like driving on wet tyres in Formula 1 when it's dry. It is to be expected that all teams will design more or less all-round foils. That way we will have reasonable races with comparable speeds. This is also indicated by what we see in the tests with the LEQ12 boats: They have all developed in similar, moderate directions.

Isn't the higher weight of offshore boats like the Imocas and Ultims a problem, as they have to be much thicker as a result?

Thickness is always a problem with foils. The cavitation speed is determined by the percentage thickness. This means that a foil that is eleven per cent thick in relation to the chord length cavitates at 48 knots, one that is 16 per cent thick at 38 knots. This is the relative thickness. And of course you want to reduce the wetted surface area. For example, you need to have five centimetres of thickness for strength reasons so that the foil doesn't break. If you then choose a ten per cent profile, that means a chord length of 50 centimetres. At 20 per cent, that means only 25 centimetres of chord length. So it's always about finding the best compromise between the expected cavitation and speed. Fast foils have to be thinner, but the wetted area is larger. This is why Imoca foils are around 14 per cent thick, SailGP foils around ten per cent. But it can be said that all foils, whether Imoca, Ultim, SailGP or America's Cup, are at the strength limit.

Does it actually make a big difference between the Imocas and the other foilers that they don't have T-foils on the rudders? This means they don't fly as stable as an America's Cupper, for example.

Yes, that makes a big difference. The lack of a T-rudder on the Imocas means that the stern sinks when the boat starts to fly. This increases the angle of attack of the main foil, too much lift is generated and the boat shoots out of the water at the front until it stalls on the main wing. The boat crashes down. So you don't achieve stable, long flight phases as with America's Cup, SailGP boats or the Ultims.

In a recent YACHT interview on the launch of the Ultims, Charles Caudrelier said that there will be no T-foils on offshore boats because they only work if they are regulated all the time, which a single-handed skipper can never do, and automatic systems are banned. Is that the case?

Yes, they need foils that regulate their own altitude. The first ones in the America's Cup were also like this, these J-foils. It works like this: There is always an angle between the foil shaft, which is actually always in the boat, and the tip: the tip goes inwards and slightly upwards. If you then sail and the boat flies at a certain height and the foil comes further out of the water due to more speed or a wave, it reduces the surface area of the shaft in the water. As a result, the drift to leeward increases. And the drift reduces the angle of attack of the water at the tip. This causes the foil to lose buoyancy and the boat sinks again. The drift decreases and the whole process is now repeated, but in the opposite direction.

How complex is the regulation with T-foils in the America's Cup in comparison?

This is a full-time job. Typically, one crew member adjusts the angle of the flaps at the end of the foil once a second. The team member concentrates on nothing else. Of course, this is not possible with an Ultim or Imoca.

One would have expected a dramatic improvement in the Etmal with the Ultims, which are fully foiling. Why doesn't the existing mark fall?

On the other hand, the days on which the Tris manage 700 miles have increased significantly. The improvements are more to be found in the average speeds and the control of the boats. For example, the Ultims now all have a T-foil at the bottom of the centreboard in the main hull. This allows the righting moment and the flight altitude to be actively controlled. This means that if the hull sinks, the foil is set to lift and pushes the boat out. If you have too much pressure and perhaps need to open the sheet sooner, you can set the T-Foil to downforce, which then pulls the boat down and immediately increases the righting moment. This is easier with a simple adjustment of the foil than opening the sheets and laboriously tightening them again.

Another question on the subject of cavitation. The imploding vapour bubbles damage the material of the foil. How strong is the effect and how long does it take for the damage to become critical?

This can happen very quickly, not in minutes, but in hours. Temperatures of up to several hundred degrees can occur during the implosion of the vapour bubbles. This damages the material and can cause holes or delamination. For this reason, the foils are designed so that cavitation occurs as far back as possible at high speed, i.e. the implosions start behind the profile.

What actually happens during the high-speed record attempts? The Swiss team SP80 is currently trying to break the record of 65.45 knots set by Paul Larsen's British team Sailrocket in 2012 and has set its sights on getting close to the 80-knot mark. Paul Larsen told YACHT that they have already used "ventilating foils". Now the Swiss are even talking about "super ventilating foils". What does that mean?

A distinction must be made between the two phenomena of cavitation and ventilation. Cavitation refers to the effect when the water on the foil evaporates. Ventilation means that the wing draws in air from the water surface. With a foil that ventilates, the negative pressure side works in air. With a foil that cavitates, the negative pressure side works in water vapour.

The profiles of Sailrocket or now probably also of SP80 pierce the water surface, and at very high speeds cavitation sets in, which leads to ventilation until the foil ventilates completely on the underpressure side, i.e. over the entire surface. You lose the suction effect on the underpressure side, but the overpressure on the other side means that a force is still generated, albeit a smaller one. It is important to realise that the foils on boats work differently: They do not push the boat out of the water, but pull it in, keeping it in the water. In both the Sailrocket and the kite models, the sail pulls the boat strongly upwards. This means that the foil guarantees contact with the water. In the case of Sailrocket, the top worked completely in the air, only the bottom worked in the water. When they didn't have this under control at the beginning, the boat took off and flipped over in the air for precisely this reason.

So what is the advantage of these ventilating foils?

You have no choice, at speeds above 60 knots a foil simply no longer works for liquid water. So you have to make sure that at least the overpressure side is still working. Once you are in this range, there is basically no physical limit to even higher speeds. Such profiles also look very different from foils that are only supposed to work in liquid water. They are very pointed at the front and blunt at the back, almost like a wedge. The problem, however, is that such foils are very poor in the low speed ranges, i.e. from zero to 30 or so. The sail area is rather small for high speed. It took Sailrocket a long time to make this transition under their own steam; they fiddled around at 30 knots for years. When they finally got above 40, they very quickly reached the record of 65 knots.

So far, the fastest sailing boats have been seen in relation to wind speed. The SailGP and America's Cup boats sail somewhere between three and four times the wind speed, the land and ice sailors at six to eight times. What else is there in sailing?

The speed record boats actually have a very poor efficiency factor in this respect. They are more like two to two and a half times the wind speed. That's why they are also dependent on these high-speed wind spots such as the Lüderitz Canal off Namibia or the Mistral wind corridors in the Mediterranean. The factor between wind and boat speed depends primarily on the ratio of lift to drag. If the latter is good, the former is also good. But this ratio is much, much worse with ventilating foils than with normal profiles. A normal foil could achieve ratios of 1:20, a hyperventilating foil is already well served at 1:5.

It's even worse with the surfers. They reach 50 knots in about 50 knots of wind, so the ratio is almost 1:1, which is why you can't make great leaps. And of course, the aerodynamics of a windsurfer are simply miserable due to the rider in the wind, arms outstretched and all. Hydro and aerodynamics play equal roles at speed.

Good keyword: the Ultims have recently seen massive investment in improving their aerodynamics: The trees were given fairings right up to the deck, so-called deck sweepers, so that the end plate effect works to reduce turbulence. How important is this in the America's Cup?

Hugely important. In the Cup, we will see that the boats are all completely optimised aerodynamically. Aerodynamics is almost more important than hydrodynamics. For example, the rudder is optimised from an aerodynamic point of view. It comes out of the water with the shaft when foiling. The part is then optimised for air resistance, not water resistance.

About the material of the foils: the new ones on the SailGP are now made of titanium instead of carbon fibre, while the Imocas and Ultims are elaborate laminates made of hundreds of layers of carbon fibre. Construction is so expensive and time-consuming. What about the Cup?

The foils really take ages to build, one takes months. They are milled from steel, which means they can be even thinner. This is high-strength steel that has to be specially forged and treated. Milling then takes a very long time as the steel is extremely hard.

There are many sources of error when laminating carbon fibre foils: Resin content, air pockets, contact pressure. Is it much easier with steel?

Exactly. With metal, the risk of something going wrong is much lower.

Let's keep our fingers crossed that this Cup will be more exciting and closer than last time.

We would prefer it not to be exciting. If we dominate so much that the others have no chance, that would be okay with me (laughs). England have been trying to win the Cup for 170 years, it's about time!

Other interesting foil articles:

• "FLYINGNIKKA": On board the 60-foot foiler - "like a GT sports car"
• LA BOULANGÈRE MINI-TRANSAT 2023: Federico wins, the foilers lose
• BALTIC 111: "Raven" achieves 29 knots with foils at the first attempt

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Voodoo Yachts introduces high-speed and "exceptionally efficient" catamaran model

New Zealand-based Voodoo Yachts has announced a new, hydrofoil-assisted catamaran model known as the XF95. 

The largest entry in the Xpedition Foiler range, the 28.5-metre model is based on the same proven, pioneering platform as the shipyard's previous models which have been "tested and battle-hardened in the South Pacific". The XF95 is characterised by a new exterior style, including forward raked windscreens, "exceptional efficiency" and an impressive top speed of 40 knots.

"This speed is unique in the adventure superyacht market, and a combination which grants the owners much more freedom. To our knowledge, this will be the largest high-speed hydrofoiling luxury motor yacht in the world," said Voodoo Yachts co-founder and director Mitch Pachoud. "[And] with the foil she will ride unlike anything else of this size, sitting high and smooth in the water."

Key numbers include a volume of 245GT, a 9.5-metre beam and 500 square metres of on board space, comparable to builds in the 36 to 38-metre sector. The model is highly customisable, from the exterior – which can feature an enclosed or open bridge – to the layout, which offers several configurations.

For instance, the main saloon can be arranged with or without a formal dining and lounge space, while the upper deck has an optional configuration that includes a cocktail bar. Accommodation is also customisable, with one particular configuration featuring an owner's cabin adjacent to a sauna and a gym. There is also the option to include a home theatre or increase the owner's suite to fit the yacht's full beam.

Other model highlights include the main deck aft, which features a dip pool, lounge area and a swim platform with sunloungers. The garage can store a Williams Dieseljet 625 plus two full-sized Jet Skis.

"We have focused on designing a boat that will easily adapt to a wide range of climates and cruising locations, including the Med, the Caribbean, the Middle East, New Zealand and Australia," added Pachoud. "This will be a sensationally special yacht, and completely unique. There is nothing else out there that's like the XF95 at this size."

The XF95 model will also offer "environmentally friendly" options, including a large solar power array.

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Published on June 2nd, 2017 | by Assoc Editor

Foiling and Foil Shapes, a Beginner’s Guide

Published on June 2nd, 2017 by Assoc Editor -->

by Mark Chisnell, Land Rover BAR The rules covering the design and construction of the team’s America’s Cup Class (ACC) boat have defined many of the parts of the boat, including the hull and crossbeams (together called the platform), and the wing shape and size. What’s left for the team’s designers and engineers to work on is principally the daggerboards and rudders, and the control systems that operate them along with the wingsail.

A lot of the technology that goes into the control systems is hidden well inside the hull, with just glimpses of the HMI (human machine interface) that the sailors use to control the board rake, wing trim and so on. The foils are on full view however, so we thought a beginners guide to ACC foil design would come in useful now the racing is approaching.

Basic Principles The foils use exactly the same scientific principles as an aircraft wing. Just as an aircraft wing will lift a plane up off the ground, the foils of an America’s Cup Class boat will lift it out of the water. Wings are foils too, called aerofoils because they work in air. The foils on the new America’s Cup boats are more accurately called hydrofoils, because they work in water.

The secret to both types of foil is the shape – aerofoils and hydrofoils use a special shape to guide the wind or water around them, and generate the lifting force to get planes and boats up in the air. Of course, the America’s Cup boats also use an aerofoil. The main wingsail works exactly the same way as an aircraft wing, it’s just rotated to stand up straight, rather than lie flat.

While an aircraft needs an engine to push the air over the wing fast enough to generate enough force to lift the aircraft up off the ground, the wingsail on the Cup boat generates force from the wind blowing past it. The harder the wind blows, the more force it makes to push the boat forward. When the boat is going fast enough, the hydrofoils will then be able to create enough force to lift the boat out of the water. This reduces resistance to the forward motion and the boat goes faster still.

There are four hydrofoils on the boat — we count the rudders at the back because they have small wings at the tips called elevators. However, the real power to keep the boat in the air comes from the hydrofoils (the daggerboards, as you will often hear them called by the sailors) and we will concentrate on these.

The L-Foil The L-foil is exactly that; a vertical daggerboard shaft that goes through the hull of the boat, with a single horizontal hydrofoil on the bottom, the whole thing shaped like an ‘L’. If nothing else changes, then the L-foil keeps generating lift as the boat goes faster and so the boat keeps rising, and as it rises, less and less of the daggerboard is in the water.

At the basic level, two things then happen: firstly, the boat starts to slip sideways because there is less of the vertical part of the daggerboard in the water and this makes the boat feel unstable and hard to steer. Then, ultimately, if the boat keeps rising the horizontal part of the board that is doing all the lifting will break the surface. If it does, there will be a catastrophic loss of lift and the boat will come crashing back down.

Aircraft use moving parts on the foils to control the amount of lift – trailing edge flaps — but the rules forbid these on the ACC boats, so to maintain stable flight the sailors change the rake or angle of attack of the whole dagger board (and hence the foil) to the water.

Rake If you rake the board backwards as the boat accelerates, the lift will reduce and the boat will come to an equilibrium at a steady height above the water. This is all well and good until the conditions change, maybe the wind speed goes up or down, or the boat hits some waves. When that happens the rake will need further adjustment to find the new equilibrium… until the next puff or lull when it must change again.

In the big breeze and rough water of San Francisco Bay in the 34th America’s Cup it turned out that these moments of equilibrium didn’t last very long and on occasions barely existed at all. The crew’s ability to generate the hydraulic power to change the board and wing trim was simply overwhelmed; they couldn’t achieve stable flight.

V-foil The solution was what’s called the V-foil, in which the horizontal part of the ‘L’ is angled upwards to form more of a ‘V’ shape (the angle at the bottom of the ‘V’ is called the dihedral – a dihedral of 90 degrees would define an L-foil, less than that is progressively more of a V-foil).

The V-foil uses the same principle as one of the most successful original foiling powerboats. The grand old man of 19th century innovation, Alexander Graham Bell put a couple of 350hp engines on the back of what was called HD-4 and set a new marine world speed record in 1919 of just over 70mph.

HD-4 used three ‘ladders’ of small foils, one at the front, and one each side close to the back. When the boat accelerated it started to lift out of the water, and as it lifted, one by one the ‘rungs’ of the foils would break clear of the water. As they did so the lift would decrease, and unless the boat continued to accelerate the boat would stop rising and settle at an equilibrium.

The V-foil achieves this same effect with a single foil and is used in the commercial application of fast ferries— one runs between Southampton and Cowes on the Isle of Wight, right across the Solent waters where the team train, and has done so (on and off) since 1969 – so V-foils are well understood.

When a boat equipped with a V-foil keeps rising as more lift is generated by faster speeds, both parts of the ‘V’ come out of the water together. Critically, when the ‘horizontal’ section starts to break the surface at the tip, it has the effect of reducing the lift gradually, because it doesn’t all come out of the water together. So the boat comes back down gently, working towards an equilibrium ‘ride height’ of its own accord.

It might be that it doesn’t reach this equilibrium before something else changes, but the V-foil has some inherent stability (unlike the L-foil) that doesn’t require human intervention. The shape provides a feedback mechanism to control the amount of lift and produce a more stable ride at a consistent height above the water. The downside of the V-foil is that it will generate less lift and more drag than the L-foil under the same conditions, because some of the lift generated is pushing sideways rather than up.

So one of the big questions facing the teams at the outset of this campaign was whether or not the sailors could achieve stable flight with an L-foil in the new boats and the new venue. Bermuda was a very different place to San Francisco; the winds were expected to be lighter, the water flatter and it seemed that stable flight should be easier to achieve with an L-foil under human control.

A huge amount of work has gone into foil and control system design and we now know that the answer is yes, they can – all the teams are using L-foils, often with unloaded dihedral angles of greater than 90 degrees. These angles close as the boat sails and the foil is loaded up to become much closer to, or 90 degrees.

Cant Another buzz word for the 35th America’s Cup is the cant. The cant of the board is similar to the rake, except that the bottom of the board is moving sideways across the boat, to and from the centreline, rather than backwards and forwards. When the board is canted outwards (towards the edge of the boat) it creates greater ‘righting moment’ and more power to drive the boat forwards.

Righting Moment When the wind hits a sail it creates the force to move the boat forward but it also creates a force that is trying to tip the boat over. If you have ever seen a dinghy or yacht knocked flat by a big gust of wind then you’ve already got the idea.

It’s considerably simplified, but essentially the more force that can be applied to resist the wind’s effort to tip the boat over, then the faster the boat will go, because more of the wind’s energy can be captured and applied to forward motion. The resisting force is called the righting moment and creating as much righting moment as possible is a fundamental principle of designing fast sailboats. It’s the reason that you see people leaning over the windward side when they are racing, putting bodies as far out on the windward side as possible is creating righting moment.

S-Foil Finally, there’s the question of whether the vertical part of the daggerboard should be straight or ‘S’ shaped. The curve of the S-foil could be used — like the cant — to move the bottom of the board outboard and increase the righting moment. So S-foils are more powerful, but they are also more difficult to use. The curves have to raised up and down through the bearings and internal mechanisms in the hull, and that means a lot of work to keep the friction down and the efficiency high.

Tags: AC35 , America's Cup , foiling , Land Rover BAR , Mark Chisnell

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Welcome to Barcelona. Now leave. →

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Hydrofoils: Boats That Fly

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Hydrofoils make everything from water skis to sailboats to giant ferries faster (much faster). But how the heck do they work?

Oracle Team USA's AC50 "flying" at nearly 50 mph. (Photo: Ricardo Pinto)

Ever wonder why a sleek, powerful recreational boat is not even as fast as a typical economy car? It has to do with friction. An economy car needs a little over 100 horsepower to speed by at 100 mph, but pushing a boat through the water that fast takes several hundred horsepower. The reason is that water is almost 800 times denser than air.

Imagine standing on your dock in a 10-knot wind — it's not hard to do. Now imagine being in a river trying to stand up to a 10-knot current. The water is so much denser that no matter how strong you are, you'd be swept away. A boat hull has to push through all that dense water while a car can slip through the air much easier.

Planing boats are able to go faster than displacement boats because they lift part of their hull out of the water as they race over their bow wave, but there's still a lot of friction from the water on the rest of the hull. If you could get the hull all the way out of the water, you'd eliminate that friction, and the boat could go faster with the same amount of power.

The Science

Most of us have a pretty good understanding of how an airplane flies. As air flows over and under the wings (also called airfoils), it creates lift. Once an airplane is going fast enough, the lift that the wings create allow it to rise above the earth.

If you were to mount a wing or two (called hydrofoils) under a boat, all that dense water can be put to good use by pushing the boat's hull out of the water. Then friction only acts on the small foils, not on the whole hull, which is why a 130-foot hydrofoiling sailboat can "fly" at over 50 knots. Powerboats have added friction from the propulsion system that has to remain in the water, but even then, large hydrofoiling ferries can exceed 45 knots.

Speed is not the only advantage that hydrofoils give boats. Because the hull is out of the water, all the energy from waves that would normally pound against the boat pass harmlessly underneath it, creating an eerily smooth ride. Even so, hydrofoiling is typically best in somewhat protected waters.

Don't look for hydrofoils on your next runabout anytime soon because they're much more difficult to engineer and typically triple the cost of a boat. The good news is that there are other ways to 'foil that are affordable — see "Experience Hydrofoiling For Yourself" at below.

Experience Hydrofoiling For Yourself

Hydrofoil kiteboards.

If you've even seen a kiteboard zooming in a strong breeze, you know they're plenty fast. Add a hydrofoil, and suddenly you add a new dimension. These boards take lots of skill and practice to master, but the ride is said to be much smoother and even faster than a conventional kiteboard. Cost starts at around $1,000.

Hydrofoil Waterskis

These single-ski hydrofoils are really a sit-on-ski, and once you've mastered the technique, the foils will lift you up and you'll be "flying." Unlike conventional skis, these aren't designed for speed, and 18 mph is where they typically "liftoff' and suggested top speed is about 25 mph. It's also important not to ski in shallow water due to the depth of the foils. Cost is typically $1,500 and up.

Hydrofoil Windsurfers

Not content to take a surfboard and add a sail, windsurfers developed foils that allow the board to "levitate." The biggest advantage is the smoothness of the ride — a real benefit because these rigs usually sail in very strong winds with plenty of chop. Cost is about $2,500 to get started.

Hydrofoiling Small Sailboats

You don't have to spend millions on a boat like the America's Cup racers if you want to hydrofoil. The Waszp costs about $10,000, though even for dinghy racers, there's a learning curve to get these boats on their foils, with speeds up to 27 mph.

Note that most companies suggest wearing a helmet when using foiling products because of the speeds achievable and the hard, sharp foils these devices have.

Foiling The Competition

America's Cup boats are often what people think of when they hear the word "hydrofoil." Hal Youngren, an aeronautical engineer and one of the designers for the 2013 and 2017 America's Cup racers, says the difference in speed that foils make is impressive. The fastest nonfoiling catamarans in previous races could barely reach 35 knots, while the 2017 foiling cats hit 50 knots. Youngren says that these 50-foot cats are able to lift their hulls completely out of the water using only about three-quarters of a square meter of foil area (about the size of a medium-sized TV). Below about 15 knots, he says, the boats sail much like a nonfoiling boat with hulls in the water, but once over that speed, the boats start to "fly" and their speed dramatically increases.

The America's Cup Class AC75 Boat Concept Revealed

An exciting new era in America's Cup racing was unveiled in November 2017 as the concept for the AC75, the class of boat to be sailed in the 36th America's Cup is released illustrating a bold and modern vision for high performance fully foiling monohull racing yachts.

The America's Cup AC75 Boat Concept Revealed

The Emirates Team New Zealand and Luna Rossa design teams spent the previous four months evaluating a wide range of monohull concepts. Their goals have been to design a class that will be challenging and demanding to sail, rewarding the top level of skill for the crews; this concept could become the future of racing and even cruising monohulls beyond the America's Cup.

The AC75 combines extremely high-performance sailing and great match racing with the safety of a boat that can right itself in the event of a capsize. The groundbreaking concept is achieved through the use of twin canting T-foils, ballasted to provide righting-moment when sailing, and roll stability at low speed.

An underlying principle has been to provide affordable and sustainable technology "trickle down" to other sailing classes and yachts. While recent America's Cup multihulls have benefitted from the power and control of rigid wing sails, there has been no transfer of this technology to the rigs of other sailing classes. In tandem with the innovations of the foiling system, Emirates Team New Zealand and Luna Rossa are investigating a number of possible innovations for the AC75's rig, with the requirement that the rig need not be craned in and out each day. This research work is ongoing as different concepts are evaluated, and details will be released with the AC75 Class Rule before March 31, 2018.

The America's Cup is a match race and creating a class that will provide challenging match racing has been the goal from the start. The AC75 will foil-tack and foil-gybe with only small maneuvering losses, and given the speed and the ease at which the boats can turn the classic pre-starts of the America's Cup are set to make an exciting comeback. Sail handling will also become important, with cross-overs to code zero sails in light wind conditions.

A huge number of ideas have been considered in the quest to define a class that will be extremely exciting to sail and provide great match racing, but the final decision was an easy one: the concept being announced was a clear winner, and both teams are eager to be introducing the AC75 for the 36th America's Cup in 2021. — AmericasCup.com

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It’s a Boat. It’s a Plane. It’s a Hydrofoil Boat: What Is It, How It Works, & Why Buy One! 

Table of Contents

Last Updated on June 5, 2024 by Boatsetter Team

We’ve created this helpful guide to introduce new and experienced boaters to the facts and features of hydrofoil boats. We’ll delve into the practical aspects and explore the advantages and considerations they bring. Whether you’re drawn to the efficiency of the design or the promise of smoother rides, hydrofoil boats might be just the subtle yet impactful change you’re looking for in your boating ventures. Post summary: 

• What are hydrofoil boats & the works 
• Why choose a hydrofoil boat 
• What to consider before buying 

Rent. List. Share—Only at Boatsetter  

What are hydrofoil boats & the works 

A hydrofoil boat is a watercraft equipped with wing-like structures mounted beneath the hull . The hydrofoils generate lift as the boat accelerates, causing the hull to rise above the water’s surface. 

Decreasing the hull’s contact area with the water helps to reduce hydrodynamic drag and wave resistance and increases fuel efficiency. Vessels can achieve higher speeds for longer distances, making hydrofoil boats ideal for applications like ferry services and long-distance travel. 

The concept of the hydrofoil boat emerged in the early twentieth century. Today, this innovation offers a thrilling option for boaters seeking a unique, efficient, and more environmentally friendly boating experience. Pro tip: On Boatsetter , you can browse through 20,000 different makes & models of boats! 

Why choose a hydrofoil boat

Three words: Speed, stability, and maneuverability!

1. Speed  

The lift generated by hydrofoils allows these vessels to glide effortlessly, offering a thrilling experience for adrenaline-seeking boaters. Speed comes with improved fuel efficiency, which makes hydrofoil boats an eco-friendly option as well. 

2. Stability  

Whether you’re facing calm waters or challenging sea conditions, lifting above the water surface minimizes the impact of waves on hydrofoil boats. This provides a smoother ride and enhanced stability, which makes for a more comfortable and enjoyable voyage. 

3. Maneuverability  

Hydrofoil boats excel in maneuverability, offering a dynamic and agile experience on the water. Lifting enables quick and precise movements, making hydrofoil boats a preferred choice for boaters who appreciate responsive navigation.  

What to consider when buying a hydrofoil boat

Complex design = Complex maintenance

The intricate design of hydrofoil boats, including the hydrofoils themselves and control systems, demands careful maintenance and technical expertise . Boaters should be prepared for higher maintenance costs and the need for specialized knowledge to keep the vessel in premium condition. 

Weather sensitivity

While hydrofoil boats perform admirably in various water conditions, they can be sensitive to extreme weather, especially strong winds. The hulls of traditional vessels remain fully submerged in water, which means they face more resistance on the water during strong winds. Hydrofoil boats are lifted out of the water, which means strong winds pose more of a threat to the boat’s stability and control. So, when you set sail in a hydrofoil boat you’ll want to be sure to carefully consider the weather conditions.  

Initial cost investment

The advanced technology, specialized materials, and intricate design that contribute to hydrofoil boats’ uniqueness also add to their price tag. Hydrofoil boats often have a higher initial cost compared to traditional vessels, so you should be sure to weigh the upfront investment against the long-term benefits. Pro tip: Trying to figure out budgeting to buy a boat? Read How to Rent Out Your Boat? (How Much Can You Actually Make?)  

Ready to try hydrofoil boating?

Hydrofoil boats offer an exhilarating experience for boaters seeking speed, efficiency, and stability on the water. Whether you’re looking for a quick thrill or want a more fuel-efficient option for your long-distance trips, we recommend giving hydrofoil boats a chance. 

Boatsetter boat rentals provide the perfect solution for those eager to try hydrofoil boating without committing to ownership. Seize the opportunity to experience the excitement firsthand and ensure your next adventure is not just a boat ride, but a hydrofoil-powered journey.

For more information, click here ! 

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Hydrofoil Boat: All You Need to Know [2023]

• November 11, 2023
• Hydrofoil Basics

Are you ready to take your hydrofoil boarding to the next level? Look no further than the hydrofoil boat! In this comprehensive guide, we’ll dive deep into the world of hydrofoil boats, exploring their history, mechanics, and everything in between. Get ready to soar above the water like never before!

Table of Contents

Quick answer, quick tips and facts, background and history, how does a hydrofoil boat work, advantages of hydrofoil boats, disadvantages of hydrofoil boats, hydrofoil boats in sailing and sports, hydrofoil boats for modern passenger transportation, recommended links, reference links.

A hydrofoil boat is a watercraft equipped with hydrofoils, which are wing-like structures that lift the boat’s hull out of the water at high speeds. This reduces drag and allows the boat to glide smoothly above the water’s surface. Hydrofoil boats offer increased speed, fuel efficiency, and a thrilling ride for water sports enthusiasts.

CHECK PRICE on:

• Hydrofoil boats can reach speeds of up to 60 knots (69 mph), depending on the model and conditions.
• The first hydrofoil boat was developed in the early 20th century by Italian engineer Enrico Forlanini.
• Hydrofoil boats are commonly used in military applications, sailing, and passenger transportation.
• Hydrofoil boats require skilled handling due to their unique characteristics and increased speed.
• The hydrofoil technology used in boats is similar to that used in aircraft, allowing for efficient lift and reduced drag.

Hydrofoil boats have a fascinating history that dates back over a century. The concept of using hydrofoils to lift boats out of the water and reduce drag was first explored by Enrico Forlanini, an Italian engineer, in the early 1900s. Forlanini’s early experiments laid the foundation for the development of hydrofoil technology.

During World War II, hydrofoil boats gained prominence in military applications. The high speed and maneuverability offered by hydrofoils made them ideal for patrol and attack missions. After the war, hydrofoil technology continued to evolve, and hydrofoil boats found their way into civilian use.

Hydrofoil boats work on the principle of hydrodynamics. The hydrofoils, which are typically located beneath the hull, generate lift as the boat gains speed. This lift raises the hull out of the water, reducing drag and allowing the boat to glide smoothly above the surface.

The hydrofoils themselves are wing-like structures with a curved shape. As water flows over the curved surface of the hydrofoil, it creates a pressure difference that generates lift. This lift counteracts the weight of the boat, allowing it to rise above the water.

To control the hydrofoil boat, various mechanisms are employed, including adjustable flaps and trim tabs. These allow the pilot to adjust the angle of attack and the lift generated by the hydrofoils, providing stability and control.

Hydrofoil boats offer several advantages over traditional watercraft. Here are some of the key benefits:

Increased Speed : Hydrofoil boats can achieve higher speeds than conventional boats due to reduced drag and improved efficiency. This makes them ideal for racing and water sports.

Fuel Efficiency : The reduced drag of hydrofoil boats translates into improved fuel efficiency. By gliding above the water’s surface, hydrofoil boats require less power to maintain high speeds, resulting in lower fuel consumption.

Smooth Ride : The hydrofoil design allows hydrofoil boats to glide smoothly above the water, minimizing the impact of waves and choppy conditions. This provides a more comfortable and enjoyable ride for passengers.

Maneuverability : Hydrofoil boats are highly maneuverable, thanks to their ability to quickly change direction and adjust their height above the water. This makes them ideal for navigating tight spaces and performing agile maneuvers.

While hydrofoil boats offer many advantages, they also come with a few drawbacks. It’s important to consider these factors before investing in a hydrofoil boat:

Cost : Hydrofoil boats tend to be more expensive than traditional boats due to the additional technology and engineering involved. The initial purchase price, as well as maintenance and repair costs, can be higher.

Skill Requirements : Operating a hydrofoil boat requires specialized skills and training. The unique characteristics of hydrofoil boats, such as increased speed and maneuverability, demand a higher level of expertise from the pilot.

Limited Use in Rough Conditions : While hydrofoil boats excel in calm and moderate conditions, they may not perform as well in rough seas. The lift generated by the hydrofoils can be affected by large waves, making the ride less stable and potentially uncomfortable.

Hydrofoil technology has revolutionized the world of sailing and water sports. Sailboats equipped with hydrofoils can achieve incredible speeds and thrilling performances. The America’s Cup, one of the most prestigious sailing events, has seen the introduction of hydrofoil technology, leading to exciting races and new records.

In addition to sailing, hydrofoil boats are also used in various water sports, including kiteboarding, wakeboarding, and surfing. Hydrofoil boards allow riders to glide effortlessly above the water, opening up new possibilities for tricks and maneuvers.

Hydrofoil boats have found practical applications in modern passenger transportation. These high-speed vessels offer a faster and more efficient alternative to traditional ferries. Hydrofoil passenger boats are commonly used for commuting between islands, coastal travel, and even short-distance international travel.

The speed and comfort of hydrofoil boats make them an attractive option for travelers looking to reach their destinations quickly and enjoy a smooth ride along the way. Many popular tourist destinations around the world offer hydrofoil boat services to enhance the travel experience.

What does a hydrofoil do for a boat?

A hydrofoil lifts a boat’s hull out of the water, reducing drag and allowing the boat to glide above the surface. This results in increased speed, improved fuel efficiency, and a smoother ride.

Read more about “… What is the Purpose of a Hydrofoil? All You Need to Know About Hydrofoiling™”

How much does a hydrofoil boat cost?

The cost of a hydrofoil boat can vary greatly depending on the size, model, and features. Entry-level hydrofoil boats can start around $50,000, while high-end models can cost several million dollars.

Read more about “… Hydrofoil for Sale: Your Ultimate Guide to Hydrofoil Boarding”

What are the disadvantages of hydrofoils?

Some disadvantages of hydrofoil boats include higher costs, the need for specialized skills to operate, and reduced performance in rough conditions.

Read more about “How Does a Hydrofoil Work on an Outboard Motor? …”

How fast can a hydrofoil boat go?

Hydrofoil boats can reach impressive speeds, with some models capable of exceeding 60 knots (69 mph). The actual speed depends on factors such as the boat’s design, engine power, and water conditions.

Read more about “… Hydrofoil Speed Boat: The Future of High-Speed Water Travel”

Hydrofoil boats offer an exhilarating and efficient way to navigate the water. With their ability to glide above the surface, hydrofoil boats provide increased speed, fuel efficiency, and a smooth ride. While they may come with a higher price tag and require specialized skills, the benefits they offer make them a worthwhile investment for water sports enthusiasts and those seeking fast and comfortable transportation on the water.

So, if you’re ready to take your hydrofoil boarding to new heights, consider adding a hydrofoil boat to your arsenal. Get ready to soar above the water and experience the thrill of hydrofoil technology!

• Hydrofoil History
• Advanced Hydrofoiling Techniques
• Hydrofoil Equipment Reviews
• How Does a Hydrofoil Work on an Outboard Motor? 2023
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• Shop Hydrofoil Boats on: Amazon | Walmart | Etsy
• Shop Hydrofoil Equipment on: Amazon | Walmart | Etsy
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Best hydrofoil boats: 6 of the most spectacular foiling motorboats money can buy

• Electric boats
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Foiling technology has really taken off in the past few years. We pick out 6 of the best hydrofoil boats you can buy right now…

With its roots in the 19th century, foiling technology is as old as the hills, but in the past five years we’ve noticed an explosion of hydrofoil boats coming onto the market.

In part inspired by the foiling raceboats of the America’s Cup , the popularity of foiling is easy to understand – fuel efficiency gains are substantial, noise is almost eliminated (particularly if your foiling boat also happens to be an electric boat ) and they look as cool as a snowman in a freezer!

To help you understand the dizzying array of foiling boats available right now, we’ve put together the following guide to what we think are the most promising designs out there.

6 of the best hydrofoil boats

SEAir foiling RIB

Founded in 2016, French yard SEAir builds foiling RIBs, having been inspired by the speed of foiling racing yachts.

We tested their 5.5m model back in 2018 and since then they have expanded their range to cover superyacht chase boats, commercial and military vessels.

Our tester recorded a top speed of 32 knots, with the foils doing their best work at around 20 knots, but SEAir claims that 42 knots is possible in the right conditions.

Read more about the SEAir foiling RIB

Article continues below…

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A dual helm set-up allows the boat to be piloted from the bow or the cockpit. Photo: Guillaume Plisson

Enata Foiler

Dubai-based Enata Marine added a healthy dose of glamour to the world of foiling boats in 2018 with the launch of its Foiler.

In addition to a superyacht tender-worthy exterior, this 32fter includes a bow window for spectacular views while underway.

A 40-knot top speed and a 190nm range makes this a very appealing option, although the premium price tag of $938,000 may put some off.

Read more about the Enata Foiler

Princess R35

When British boatbuilding giant Princess Yachts got in on the foiling boat game in 2019 with a 35ft carbon-fibre dayboat, we knew that things had really taken off.

While the foil-assisted R35 may not have the spectacular cruising-above-the-waves appeal of some other foiling boats, it is highly efficient, beautifully designed (in collaboration with Pininfarina) and handles like nothing else we’ve ever driven.

In our review, we praised its rare combination of agility, refinement and stability, with spray kept in check impressively at high speeds.

Read more about the Princess R35

The foiling Candela C-8 is the first boat to use Candela’s proprietary C-POD, but bigger craft will follow later

Candela C-8

Swedish firm Candela burst onto the scene in 2021 with its debut, the Candela C-7 , which was billed as the world’s first electric foiling boat, but it was the 2022 launch of the Candela C-8 that really moved the game on.

Available with a 69kWh battery, adapted from the Polestar 2 electric car, owners can expect a range of 57nm at 22 knots, more than enough for dayboat use.

The consumption figures are truly staggering, with Candela’s figures suggesting that the C-8 is more than 12x more efficient than an equivalent 300hp outboard powered sportsboat.

Read more about the Candela C-8

The electric Iguana is capable of three knots on the land and 30 knots at sea

Iguana Foiler

Not content with being at the forefront of the amphibious boats market with its caterpillar-track offering, French yard Iguana has set its sights on the world of foiling too.

Announced last year, the Iguana Foiler will be powered by the world’s most powerful electric outboard engine, the 300hp Evoy Storm .

Having tested both the engine and the boat separately, we can’t wait to see the result when they come together with the added advantages of foiling technology. Watch this space…

Read more about the Iguana Foiler

The foils lift up at slow speeds to reduce the draft

Mantaray M24

Another exciting model in the hydrofoil boats pipeline, this 24ft runabout is particularly interesting is its simplicity. Unlike its main foiling rival, the Candela C-7, the Mantaray M24 requires no complicated electronics to ‘fly’.

Instead it uses the builder’s patented mechanical hydrofoil system, which it has trademarked as Dynamic Wing Technology or DWT. The technology is said to be the result of ten years’ development work and uses a retractable T-foil in the bow and H-foil amidships that self-stabilise mechanically.

This allows it to lean naturally into corners and ride serenely over waves without relying on a network of sensors and algorithms to monitor and adjust the foils. If it proves effective this could drastically reduce the cost and complexity of foiling boats, while simultaneously increasing reliability.

Read more about the Mantaray M24

It doesn’t end here, with fascinating one-off projects from Spirit Yachts and BMW on the water, it’s clear that foiling has a huge potential for transforming the world of boating.

Read more about hydrofoil technology

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• This New 94-Foot Foiling Catamaran Can Fly Across the Seas at Over 50 Knots

Voodoo's new XF95 also has a range of 3,500 nautical miles.

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Voodoo Yachts has conjured up some more marine magic.

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The X95 can be equipped with two engines rated at either 2,000 or 2,600 hp. The latter option enables a cruising speed of 37 knots and a top speed of 45 knots. Voodoo says there is also another, more powerful setup that results in a top speed of more than 50 knots. In terms of range, the vessel can cruise for 1,200 nautical miles at 30 knots or cover 3,500 nautical miles at eight knots. Owners can add a larger tank to increase the range or install a large solar array to generate clean, green power at sea.

With a beam of 31 feet and an interior volume of 245 GT, the X95 offers nearly 5,400 square feet of space on board. The yard says the spacious living quarters are on par with yachts spanning 118 to 125 feet. The model is highly customizable, too: Owners can opt for an enclosed or open bridge and choose between several different layouts.

As standard, the yacht is outfitted with five guest staterooms and two crew cabins. One configuration has a full-beam owner’s suite in the bow of the lower deck, four en suite guest cabins amidship, and a garage aft. The main deck features a large salon and dining area, while the upper deck showcases a plush lounge. Owners can add other interior features such as a sauna, gym, or home theatre.

Marine magic, indeed.

Rachel Cormack is a digital editor at Robb Report. She cut her teeth writing for HuffPost, Concrete Playground, and several other online publications in Australia, before moving to New York at the…

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Second act: Here’s how this company is propelling hydrofoils into the mainstream

Few vessels have captured the imagination quite like the hydrofoil in maritime history.

These futuristic-looking boats, skimming on wing-like foils above the waves, once seemed destined to revolutionize water transport. Yet, they remained a fringe curiosity for decades, needing more efficiency and complexity.

Now, a set of technological advancements is set to propel hydrofoils back into the spotlight, promising a sea change in how we traverse our waterways.

At the forefront of this renaissance is Eric Laakmann, CEO of Vessev , a company developing the next generation of electrically powered hydrofoils. Lockman’s explained the dramatic shift in hydrofoil capabilities.

“The new breed of hydrofoils today is totally different than what came before,” Laakmann tells Interesting Engineering . He points to the Boeing Jetfoil, launched in 1976 and still operating in Hong Kong and Macau, as an example of the old guard.

“If you look at the Jetfoil, it’s actually quite inefficient. You can see how much fuel it uses, and it literally had analog computers doing the control systems. But what do we have today? We’ve got something different,” he continued.

Catalysts for hydrofoil revolution

This “something different” results from what Lockman calls “adjacent possibilities,” a concept borrowed from evolutionary biology. As new organisms evolve based on environmental changes, technological breakthroughs often arise from developments in seemingly unrelated fields.

The America’s Cup yacht race has been a crucial catalyst for hydrofoil advancement. “You now had boats that could sail at three times the wind speed,” Laakmann explained. This push for extreme performance has led to more efficient hydrofoil designs and cheaper composite materials instead of expensive metals.

But it’s not just about aerodynamics and materials science.

The electric vehicle revolution has played a pivotal role in making hydrofoils commercially viable. “Marine’s a big industry on its own, but it’s not as big as automotive,” Laakmann noted. “And so what we’re seeing now is a trickle-down of low-cost automotive components for electrification into the marine space.”

Electric efficiency

This electrification is key to the hydrofoil’s resurgence.

Electric motors offer inherent efficiency advantages over traditional combustion engines. When combined with the drag reduction achieved by lifting the hull out of the water, the result is a quantum leap in overall efficiency.

Laakmann cites figures as high as 90 percent lower operational costs than traditional ferries.

To put this in perspective, Laakmann offered a comparison: “We have a chase boat that we have been using during development and testing. It does all the same routes, all the same exact runs that we do. Exact same speeds. After almost every day of testing, we would put 15 times more cost in fuel in the chase boat than electricity in the VS9 hydrofoil.”

The economics are compelling. “Electricity is so much less expensive than fossil fuels,” Laakmann explains. “If you equate the costs of electricity, kilowatt hours to usable kilowatt hours in fossil fuels, it’s roughly three to five times more expensive. So that’s why electric cars are cheaper. But then we have this other hack, which is the hydrofoiling, removing the boat from the water completely. And that it’s up to a five times increase in efficiency.”

When these factors are combined—the efficiency of electric propulsion and the drag reduction of hydro foiling—the result is a dramatic cost reduction that could reshape maritime transport.

New horizons for maritime transport

However, the potential of modern hydrofoils extends beyond mere efficiency gains. The technology opens up new possibilities for routes and services that were previously impractical or impossible with traditional vessels.

“Think about smaller lakes,” Laakmann suggested. “With traditional boats, waves can make the ride unpleasant. Hydrofoils can offer a smooth, comfortable experience on those same routes, even with smaller vessels.”

This ability to provide a comfortable ride in choppy conditions could revolutionize passenger ferry services, making routes viable that were once considered too rough or uneconomical.

The innovations driving the hydrofoil renaissance aren’t limited to propulsion and hull design. Modern control systems, benefiting from robotics and drone technology advances, have dramatically improved the vessels’ stability and maneuverability.

“Whereas the computer that was on the Boeing Jetfoil took up an entire room with analog circuits, you can now buy a consumer drone for a couple hundred dollars that has all the same computing hardware,” Laakmann explained. “The math has got better in the way we control vehicles, and low-cost actuators have now become more available on the market. So what we’re seeing today is an entirely new class of vessel.”

This convergence of technologies – advanced materials, electric propulsion, and sophisticated control systems – creates a perfect storm for hydrofoil development. The result could be a paradigm shift in maritime transport, offering vessels that are faster, more efficient, and more environmentally friendly.

The environmental aspect must be balanced. As the world grapples with the urgent need to reduce carbon emissions, the maritime industry – responsible for about three percent of global greenhouse gas emissions – is under pressure to clean up its act. Electric hydrofoils could offer a solution, providing clean, efficient transport for both passengers and cargo.

Looking ahead

Of course, challenges remain. The initial cost of electric hydrofoils is likely to be higher than that of traditional vessels, and infrastructure for charging and maintenance will need to be developed. There are also regulatory hurdles to overcome as maritime authorities grapple with how to classify and regulate these new vessels.

Despite these obstacles, the future for hydrofoils looks bright. “We’re on the cusp of a revolution in maritime transport. These aren’t just faster boats; they’re cleaner, more efficient, and open up entirely new possibilities for how we move people and goods across the water,” Laakmann said.

It’s clear that the hydrofoil’s time may have finally come. What was once a fringe technology, relegated to niche applications and futuristic fantasies, could soon become a common sight on waterways worldwide.

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Sail Away on Whistler’s Alta Lake

Whistler is well known for its laid-back lake culture, with mountains, trees, docks and fresh water providing many idyllic spots to hang out and relax on a warm sunny day. What people might not know is that the north end of Alta Lake is also home to a reliable afternoon thermal, making it the perfect place to learn and practise sailing.  

The History of Sailing in Whistler

Alta Lake, formerly Summit Lake, was the site of Whistler’s first permanent tourist operation, Rainbow Lodge. Myrtle and Alex Philip, a young entrepreneurial couple from Maine, opened the fishing lodge of their dreams in 1914 on the site where Rainbow Park now sits. Geographically isolated from other communities, lodge guests arrived by train on the Pacific Great Eastern railroad. Aside from walking, illegally, along the newly formed railroad, the easiest way to get around town was by water, and boating was a core component of life at Rainbow Lodge.

Every morning fresh milk and cream had to be boated over from nearby Tapley’s Farm for guests’ breakfasts. Myrtle also relied on catching fish to feed her guests, especially in the winter when other protein sources were scarce. One winter she sprained her ankle badly, so together with her dad she rigged a rudimentary sail onto a wooden raft, allowing her to sail back and forth across the frozen lake to her fishing holes and prevent her guests from going hungry.

As Whistler became more accessible by road, sailing became less about transport and more about sport and recreation. In 1966 the Alta Lake Sailing Club was formed and operated out of the popular Cypress Lodge at the north end of Alta Lake.

Their flagship annual event, the Whistler Regatta , was first held in 1965 and continues to this day. Held in late August, it was nicknamed the “Regretta” for the regret the community feels as summer comes to a close.

The non-profit Whistler Sailing Association was formed in 2008 by a group of local dinghy* enthusiasts and continues to operate out of the same building next to The Point Artist-Run Centre. Today the association has grown into a fully accredited sailing school offering summer sailing programs for kids and youth, and adult programming including learn to sail and race nights.  

*A dinghy is a small sailboat that doesn’t have a weighted keel. They’re light, manoeuvrable boats that require more athleticism and help you to hone your skills. Most of the boats sailed in the Olympics are dinghies.

Whistler Sailing holds weekly club races throughout the summer. The Wednesday Night Races kick off at 6:15 PM and the series is open to all racing and season pass members. Drop-in attendance is allowed at a minimal fee per person and all participants must have a basic membership to the non-profit organization.

While racing is a great way to test your skills as a sailor, Whistler Sailing’s GM Francois Hebert is passionate about encouraging more people to take up sailing and is focused on teaching beginners and those looking to hone their existing techniques.

Learning to Sail in Whistler

Francois grew up sailing on the Great Lakes with his parents and learnt to sail when he was eight years old. Recently crowned the 2023 ILCA 7 US Masters National Champion, he spent many years coaching all over but saw an opportunity to start his own sailing school in Whistler because of Alta Lake’s special location. The wide expanse of fresh water, combined with the wind, makes Alta Lake the perfect place to learn to sail.

“It’s in a geographic aspect of the valley where it really narrows, creating a bit of a funnel,” Francois says. “And the temperature in the valley is what we call a thermal, so whenever Pemberton gets a couple degrees warmer than Whistler, which it typically does every afternoon, then the wind comes. It’s rare to have no wind.”

Whistler Sailing has a variety of programs for people interested in learning to sail. Kids’ week-long summer camps are held every week during July and August and cater to ages five and up. Adults have access to group lessons in June, and private lessons all summer. For those with some sailing experience, you can charter or rent a boat .

Hebert recommends taking the Hobie Wave catamaran, as “it’s a very popular two-hull boat that people are likely familiar with from visiting resorts like Club Med.”

Wing Foiling Lessons in Whistler

Anyone with a medium amount of sailing experience looking to try something different will want to consider the brand-new wing foiling lessons .   Combining elements of windsurfing, kiteboarding and surfing, wing foiling offers a unique blend of wind and water dynamics. The new sport is taking off right now and what makes it stand out, literally, from other water sports is the aeroplane technology used to achieve vertical lift.

“You have a sail basically, that’s called a wing, that you control just with your hands, so there’s no mast like a traditional windsurfer. And you stand on what’s called a hydrofoil, so you’re essentially using two wings and one of the wings is underwater,” Francois explains. ‘This little aircraft wing that works under the water pushes you all the way up until your board is flying about a metre above the surface. It’s extremely quiet and an amazing feeling, you really feel like you’re flying.”

Francois’ passion for wing foiling is palpable and it’s an experience he wants to share with others.

“It’s a really great thing that you can do on Alta Lake, it’s windy enough and there’s enough space that it’s a really good place to learn, which is why we’ve started a school for wing foiling.”

Wing foiling lessons begin on dry land, learning how to control the wing in the wind. They then progress to using the board without the foil, before putting all the equipment together for the full wing foiling experience. Whistler Sailing also offer packages that include tow foiling as a way to focus on developing hydrofoil handling skills while still progressing with wing handling.  

But, Francois is keen to point out, wing foiling is more geared towards people who have previous sailing experience.

“You need some basic sailing knowledge before going in that direction. If you’ve never sailed before it’s a bit harder because you need some water experience and notion of winds,” says Francois. “But it’s accessible to anyone with even a medium amount of sailing experience.”

After thirty years on the water, Francois credits the multi-dimensional nature of sailing for his life-long love of the sport.

“Sailing is a complex sport in many ways and you can learn new things throughout your whole life. You can always go out on the water and encounter a condition you haven’t seen before. It’s a lot of fun.”

With so many outdoor sports on offer in Whistler, it can sometimes be hard to choose between them. On those hot summer days, nothing beats the natural air conditioning of dry wind hitting cold lake water. Adding sailing to your skill set might just open up a new way to explore.

Book your summer stay between May 1 and October 31, 2024, and save up to 20% on lodging and 15% on activities. Secure your mountain getaway with Whistler.com for personalized service and the local knowledge of our Whistler-based team .  If this post has you dreaming about Whistler, enter our Feel It All in Whistler  summer contest to win a trip for two!

Like a lot of locals, Kate came to Whistler for a month, seven years ago. Originally from Australia, Kate is happily stuck in the Whistler bubble, spending their free time boarding, biking and hiking among the trees. In the summer months you can find them canoe guiding on the River of Golden Dreams.

Insider’s Guide: Whistler Mountain Suspension Bridge

Related posts, insider guide: summer hiking in whistler, whistler wildlife series – the rufous hummingbird.

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Test-driving the $59K electric hydrofoil Jet Ski, new water toy of the uber rich

The Valo Hyperfoil is a combination of surfing, flying, and riding a Harley without a helmet.

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Last week, I flew across the Brooklyn Basin in Alameda, my body skimming three feet above the water. A quick shift on the throttle and I carved left and right, taking turns at 20 mph, while seated atop the Valo Hyperfoil, a $59,000 flying electric Jet Ski.

The sensation was euphoric—a combination of surfing, flying, and riding a motorcycle with no helmet. The wind whipped my hair, and the landscape blurred as I flew, but it was a surprisingly silent ride. The electric motor was whisper-quiet compared to the metal-on-chalkboard growls of a fuel-powered Jet Ski. It was a super smooth ride as I floated above the waves, rather than plowed through them, as with Jet Ski 1.0.

It took a while to fine-tune my driving skills. When the hydrofoil reached a certain speed, its hull rose majestically out of the water, and, startled by the speed of the ascent, I released the throttle and splashed down again. Once I worked up the courage not to release the gas, I didn’t want to get off.

“That was the longest demo ride we’ve ever had,” said Ed Kearney, the boyish-faced 37-year-old founder of Valo, as I stepped back onto the dock after 20 minutes. At top speed, I’d have topped around 25 mph; Valo’s forthcoming model will reach 42 mph, according to Kearney. 

The Alameda-based company launched in 2022, spinning out of Kearney’s prior startup, Boundary Layer, which had prototyped hydrofoil cargo boats that never made it to market. To date, Kearney’s raised $7.1 million for both companies, received a Good Design award for the Hyperfoil, and has $124 million in letters of intent from ferry companies and manufacturers to deliver industrial-sized hydrofoil systems.

Valo’s hoping that gaining traction as a fun tech toy for the one percent will allow them to expand into bigger businesses, including replacing air freight shipping and passenger ferries. This would be a big environmental win, they believe; in 2022 , marine vessels released around 50 million metric tons of carbon dioxide into the atmosphere, a fraction of the 370 million tons contributed by cars, but still a lot of carbon. 

“We’d love to see folks commuting on it,” said Kearney, who plans to offer test-rides between Oakland and San Francisco Bay. “The water’s this huge untapped resource.”  (This could prove legally problematic. Barring a few exceptions, Jet Skis are not currently allowed in San Francisco Bay . The SFPD’s Marine Unit did not respond to a request for comment.)

To date, Kearney’s received around 60 pre-orders for the first batch of Valo Jet Skis, scheduled to ship in late 2024, totaling “about $3.5 million worth of product.” Of course, at $59,000 a pop, the economics aren’t quite there yet for the casual commuter—or even the avid jet skier, who can expect to spend between $5,000 and $20,000 for typical watercraft. But the hydrofoil Jet Ski isn’t just a flex for the uber-rich, emphasized Kearney: “We’re on the pathway [to] creating a transportation revolution.”

The Tesla of the water

Hydrofoiling dates back 150 years, when a Frenchman first stuck metal plows with a wide flat end (now called wings) below his rowing boat. The techniques involved in hydrofoil design changed over the years, and were revitalized by the resurgence of foils in sailing. In 2013, Larry Ellison included hydrofoiling catamarans in the America’s Cup race. Soon, Mark Zuckerberg ’s foilboarding hi-jinx made the news, and Bay Area techies went all in on electric foilboarding, essentially surfing over the water with the aid of an underwater propellor.

Valo is Kearney’s third foray into the startup world. In 2017, he moved from Sydney to San Francisco to participate in Y Combinator with Snapr, his photography-on-demand startup. “I was exposed to so much cool stuff,” he said; his YC cohort included a guy building electric 737’ s, a Fitbit for dairy cows, and a decarbonization startup. “That was the catalyst,” he said.

As a kid, Kearny and his dad had watched hours of footage of the MIT Human-Powered Hydrofoil project, and he’d dreamed about somehow bringing that tech to life one day. The move from photo app CEO to boat-trepreneur wasn’t totally out of left field: he studied civil engineering in college, followed by a master’s in oceanography and coastal engineering at the University of New South Wales.  

Kearney, who now lives in Pacific Heights, went through Y Combinator again in 2019, this time with a new company, Boundary Layer, that was developing hydrofoil ocean freighters. The goal was to replace air freight, a $100 billion industry that produces vast amounts of C02.

By demo day, he’d hacked together a working prototype and proudly presented his zero-emission hydrofoil container ship to attendees. The plan was to scale up, but the famously conservative marine industry wasn’t receptive. Kearney had raised $5 million (plus $90 million in letters of intent), but that was a drop in the ocean in the boat–building world. Building big-ass boats is expensive, he said. Their size meant they’d have to be powered by zero-emission liquid hydrogen, adding another layer of complexity. 

By 2022, Kearney’s business was looking dead in the water. “That’s when I thought, let’s go to the other end of the spectrum, and make the smallest thing we can that demonstrates our key technologies,” he said.

Enter the hydrofoil Jet Ski. It was fun, it was different, and it was perfectly timed. The Jet Ski market was thriving: In 2023, the global business for the personal watercraft was valued at $1.9 billion, with North America taking a 62% slice of that pie. “Because it’s a toy, you don’t have to present a business case,” said Kearney. “But it shows the core technology. The recreational boating industry is not very price sensitive….they spend money because they want to spend money.”

His team hacked together the Valo in six months. 

‘People like to have fun’

I rode their prototype model—Valo’s only model to date—and can confirm the flying feeling. It was incredible to float above the water and glide in near silence around Alameda’s waterfront. But the Jet Ski I drove also had a hacker-esque vibe to it which belied the $59,000 price tag. The hull appeared to be made of gray styrofoam, the rear platform had visible wires, and the overall finish looked more like an impressive stage prop than a Tesla. 

The final product will look far more polished, Kearney assured me. The Valo Founders Edition (what the company’s calling its first 60-craft run) would be a sleek, wire-free cruising machine, with a vegan leather seat and a dark silver body, able to be fully charged in three hours. The new model does away with the tri-foil design of the prototype, which has two foils at the front and one at the back, to a streamlined two-foil design.

“In the arc of startups, [you] want something that’s super differentiated and shows off the technology—and you want to get there as soon as possible,” said Alex Teng, a partner at San Francisco-based venture capital firm Fifty Years, which invested early in Kearney’s cargo freight startup. Teng said the Valo’s “awesome” to ride: “You feel so connected to the water and then it’s whoa, I’m flying.” 

On the downside, hydrofoils are harder to control than regular boats, as they’re not as stable, Teng noted. If that gets figured out, well, “there’s a whole class of boats that would like to go electric [and] hydrofoil,” he said. Advances in material science, such as carbon fiber composites and ultra-high-strength stainless steels, make this plausible at scale. “It’s a different powertrain concept than the typical internal combustion engine,” he said.  

Reo Baird, the chief technology officer for Valo, has tackled the stability question with Skyride, a control system that utilizes a stack of actuators, sensors, computers, and embedded electronics to make real-time micro-steering adjustments. “That’s really the key technology behind the vehicle,” said Baird.

Consumer interest has been huge, said Kearney, who receives weekly emails and Instagram inquiries from would-be customers. Kearney wouldn’t share any names of pre-order buyers but said they include some Saudis, a couple of Bay Area big shots, and people in Florida and Texas.

The goal is to build traction, he said, and then direct the interest back to the freight space. “[This is] our flywheel to build bigger things… [we’ll] come at the market opportunity from the other direction.” 

That seemed like a giant leap, and I pressed for more answers. “Sure, it’s not like someone’s gonna ride our Jet Ski and say, by the way, I also own an air freight company,” he said. Instead, he hopes that broader acclimatization to hydrofoils in general, via Jet Ski usage, will solidify the science for people. 

“At the end of the day, this is America,” said Kearney. “People like to have fun and people take risks. We don’t see how this is any less safe than what’s already on the market.”

Zara Stone can be reached at [email protected]

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