small sailboat with foil

12 foiling boats for sailors of all levels

• April 15, 2022
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There’s no denying that the phenomenon of the moment, when it comes to having fun, is foiling boats (as Checco Bruni told us himself in this article). In the wake of the latest editions of the America’s Cup, flying boats, especially in the dinghy segment, have become increasingly widespread. On one or two hulls, with one or more foils, more or less easy to fly, single or crewed.

We have selected for you 12 flying boats with which to enter the world of foils or with which to try and perfect your skills. We also tell you how much they cost and the “difficulty of flight” (XXX: difficult; XX: medium; X: easy). The only common denominator is that they are great fun!

Birdyfish – 4,7 m – For foiling beginners

Flying difficulty:   X

The ideal boat for learning to sail foils, even for beginners. Very few trim adjustments for foils allow you to enjoy all the excitement and joy of flying. The crew will only have to deal with sail trimming. The appendages with a soft-angled L guarantee take-off from 10 knots of wind. The shape of the bow works well even in waves. Price: 16,980 euros.

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Flo1 – 4.25 m

Flying difficulty:  X

An interesting single to approach and perfect in the world of small foilers before moving on to more sophisticated craft. Produced by the Dutch company Aeronamics, it has a soft, almost C-shaped foil. There is no adjustment of the rake of the appendages but only its extension in the water, which makes the “trim” of these appendages easy and intuitive after just a few trips. Top speeds are around 20 knots. Price: 15,495 euros.

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NACRA F20 – 6,20 m – Like America’s Cup cats

Flying difficulty:  XXX

The Nacra yard, which specializes in open catamarans and produces the Nacra 17 Olympic class, has fitted its F 20 model with a “Flight Control System” to make it fly. The Nacra 20 FCS was designed by Pete Melvin and Gino Morelli, the authors of the 2013 America’s Cup rulebook, and its foils are reminiscent of those on the AC72 in San Francisco. A very physical boat and not for everyone. Price: 34,000 euro.

Foiling Dinghy – 3,86 m – Small and versatile

It weighs 30 kilos and can be foiled as early as seven knots of wind. The Foiling Dinghy is equipped with an inverted T rudder and a pair of curved foils that act as both lifting and straightening foils, with an automatic management system. The foils have a few simple adjustments depending on what you want to achieve (more flying or more straightening). Price: 15,500 euros including taxes.

Moth – 3,35 m – The foiling cult dinghy

The progenitor of the flying dinghies is still one of the most complete single foilers on the market today. Suitable mainly for advanced sailors who already have experience on foils, it has appendages that offer multiple setting options and the possibility of being changed according to wind strength. The international class is one of the most active and always organizes very crowded races. Cult product. Price: from 20,000 euros.

Peacoq 14 – 4.70 m – Like a flying Fireball

Flying difficulty:  XX

With a hull that is vaguely reminiscent of the old Fireballs with a “cut” bow, the Peacoq 14, an evolution of the Club version, is a dinghy that can be a compromise for both novice and experienced foil sailors. In fact, the dinghies can be operated in automatic trim, or more experienced sailors can adjust their angle for maximum performance. Price: quote on request.

Persico 69F – 6,9 m – The trendy boat

This concept boat is the brainchild of the Italian racing elite (Giorgio Benussi, Dede de Luca, “l’oriundo” Maciel Cicchetti) and was designed by Argentineans Wilson and Marquinez. Flying the 69F is not too difficult, although it does require a good physique and strength in the arms, especially for the mainsail trimmer and the foil adjuster. The racing circuit has now been launched with an attractive programme. Price: rented by the season.

Skeeta – 3,35 m – Easy for anyone

Ease first. The idea behind Skeeta is the same as that of many other small foilers: to make this type of wing easy and open to everyone. Skeeta is a single glider that flies on two self-regulating appendages, not particularly technical to fly but still very high performance, with the particular shape of the hull that distinguishes all Quant models. Price: 15,345 euros.

Stunt S9 – 4,16 m – The Italian Foiling cat

This is an all-Italian One Design catamaran that can be sailed as a single with just a mainsail or even a jib depending on the weather conditions. Like other catamarans, to improve stability in flight, it moves on four submerged appendages. Physically it requires a certain amount of athleticism, also because there is a trapeze, but with a little training it can be suitable for a wide audience. Price: 16,600 euros.

Ufo – 3,00 m – Flying with two hulls

This small catamaran is equipped with a sensor that self-adjusts the inclination of the single central foil, coupled to the T of the rudder. It can take off even in light winds thanks to the lightness of its construction. The cat is quite easy to sail, suitable even for sailors who do not have much experience with foils.

The official european dealer for Foiling UFO is  Sea-Change . Price:  8.980 euros + VAT

Waszp – 3,35 m – For the whole family

Very similar to the Moth, but with one big difference: the Waszp is a monotype, it is not made of carbon and the appendages being monotyped cannot be changed. For this reason it is less expensive than the Moth, even if it does perform somewhat less well. It is considered by many to be an ideal “family” boat because it is fun for both young and old. The foil adjustment system is managed by a sensor, but it is possible to set the appendages and modify some adjustments. Price: 12,200 euros.

Whisper – 5,40 m – Full performance

As light as the highest performing Cats, it features a one-piece, non-removable platform that provides great structural rigidity. Equipped with the four classic self-adjusting appendages, it is able to set sail in light breezes with a certain ease. It is a double, with trapeze, mainsail, jib and gennaker, fast even in light winds. Physically demanding. Price: 26,900 euros.

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fulcrumspeedworks

*NOTE: Sales team will contact you with shipping rates.

WHAT IS IT?

The UFO is a simplistic modern hydrofoiling boat, that allows anyone to fly through the air, freeing the hull from draggy water. More stable than the International Moth -or even a child’s pram- with a simple rig, and a set of fully retractable hydrofoils, all for $11,500 USD the UFO makes flying attainable. Thousands less than it’s nearest competition.  Built in the United States in high volume and quality control, the UFO maintains a one-design philosophy, creating close and exciting racing on foils!

FLY WITH THE UFO

• Designed and built in the USA
• $11,500 USD
• Compatible and rewarding to all skill levels
• Lightweight for easy maneuverability
• Solid, nearly dent-proof, hull
• Unique patented hull and rig designs
• Stable on and above the water
• Small footprint for carefree storage and shipping
• Takeoff from about 8knts of wind
• Fast, fun, easy to control foiling

FUN FOR ALL AGES

The wand system controlling the foils, which can be set to fly very high, very low (even ‘no fly mode’) and all points in between. This means you can progressively add challenges to your UFO experience as you feel ready for them, from ‘beginner mode’ all the way to ‘extreme mode’. Additionally, the highly tunable sail can be set up to provide only the amount of power that your body type needs, and no excess. This means that the UFO is accessible and fun for sailors of all sizes, ages and skill levels. Merely set up the boat for your skill level and body type and go play around.

The UFO is very broadly applicable and has flown payloads from 70 pounds -a tiny kid- to 270 pounds -a tall grown man and a teenage boy-. The foil package just needs power to climb. Ultra light sailors have been caught on camera flying in 5 knots of breeze and the baseline for 225 pound sailors to take off is 10 knots. 270 flies in 12 knots of breeze.

SETUP AND BREAKDOWN

While the boat can be left on shore with everything in place, but the sail down, that doesn’t mean the UFO isn’t easy to put together or take apart. Quite the opposite. Simplicity begets simplicity and the boat is a cinch to put together and take apart.

MANAGEABILITY

Being small is it’s own reward when it comes to handling the boat through all sailing experiences. When you start to really push yourself learning to foil, there are good odds you’ll manage to capsize it. The UFO is easy to right from capsizes and even full “turtle” inversions. This last part is critical, because when catamarans are too heavy to right from turtle the only option is to make the mast float. This has the unintended downside of making the boat very likely to blow away from you. The UFO is designed to stay right alongside you in the event you are separated from the boat. Additionally, the boat possesses an uncommon “park” mode in which it will hold station of its own accord, apparently indefinitely without external input of any kind. The full benefits of that upside have not begun to be fully exploited.

FOILING AT ALL POINT OF SAIL

The Fulcrum design team strictly adhered to the axion “if there’s a point of sail (say, upwind or downwind) that it can’t always foil on, you can’t call it a foiler”. The design team achieved their goal and the UFO is a fully flying boat on all points of sail, which drastically increases its fun-factor.

At what points of sail does the UFO foil at?

The UFO fully foils at all points of sail. Upwind, downwind and reaching.  Additionally, you can set it to  not foil when you’re tired and it will do that as well, so you can get home easily. These two factors make the UFO uniquely good for learning to foil.

Who can fly the UFO?

Within reason, anyone.

UFO pilots have ranged from 8 years old to 72, from 90 pounds to 235. Young sailors do well sailing as pairs or with a middleweight to light adult. It’s rare that anyone on the fulcrum team conceives of a boat with a narrow niche in mind. Why bother? It’s a mistake in yacht design to design a boat for a narrow range of users, when for the most part people are diverse and the objective of one-design boats is to garner large fleets. That said, the boat is likely to be most satisfactory in all wind conditions in the hands of teens, small and medium men and all women. At the extreme low end of the weight range, sailors may find themselves overpowered and at the extreme high end, the wind speed required for takeoff is about two knots higher than average. UFOs have been sailed “two up” as well, though the above limits of weight range still apply to the sum of the two sailors weights.

What wind and waves can I fly a UFO in?

The UFO will sail in practically any wind condition. However, it’s important to remember that with all sailboats there are days that are great to sail in and days where you do something else.

While the UFO can at times with a skilled skipper take off in very low wind speeds, the baseline for reliable flight is around eight knots. Trying to squeeze enough power to fly out of too little wind is tiresome and in those circumstances, it’s best to do something else. In 8 knots and above, flying is magical and unforgettable. In under 8 knots, the UFO reverts to being a pleasant displacement catamaran and goes from being exciting and fast to relaxing and tactical. This is another benefit of being a catamaran.

Over the last six years the UFO has proven to be uniquely good at flying safely and consistently in very high windspeeds. In multi-class foiling regattas the UFO has proven to be the only foiler built to date that simply  loves  high windspeeds. In winds above 22 knots when other foiling boats make for shore, the UFO wants to keep playing. The upper wind limit is more a matter of taste and skill. UFOs have been sailed in 36 knots, but that requires a great deal of skill and focus.  The UFO rig having shared DNA with a windsurf rig seems to play a part in the boat’s remarkable ability to get a kick out of big wind. Since the upper wind limit on the UFO is so much higher, this makes the number of optimal days to fly a UFO (if skilled in sailing one) higher per year than with any other production foiling boat.

Most chop and wave conditions present no issue for a UFO set for the days’ conditions. After all, powered hydrofoils were first developed by various leading Navy’s as a means of smoothly flying over challenging sea-states. Choking up the ride height helps the UFO fly smoothly through the bottom of the wave pattern, undeterred. Rolling seas present even less issue, as the UFO will ride along them just like any other. Extremely tight and tall chop can be very annoying, which is not peculiar to the UFO.

Waves do effect baseline windspeeds to achieve takeoff. Imagine getting a plane to take off on a bumpy runway. This is true for all hydrofoil boats. In choppy water, ten to twelve knots can be necessary to achieve fully easy takeoffs. Some UFO sailors use aggressive kinetic techniques to overcome this and take off in choppy water and low wind.

Will I fly my first time out?

Most people do, but bear in mind that flying is a whole new experience and it takes some learning.

Conditions, setup and technique matter and if you use it incorrectly, you are likely to get some degree of incorrect results. That’s the challenge that the UFO is built to address. Over six years on the market and over 500 boats delivered, the UFO has proven to be the best and most reliable platform for ordinary sailors to reliably teach themselves foiling technique on.

What happens when I crash my UFO into something?

You’ll probably do some damage to it.

The UFO is built with durability as a core objective but it’s worth noting that the gulf between “Feather light under engineered ragged-edge high performance craft” and “literally indestructible” is extremely wide. The UFO represents neither of these extremes. Do not attempt your first flight inside a densely packed mooring field. Obstacles only make you better once you’ve mastered the basics.

How easy is it to rig a UFO?

Best in class, vs other foiling boats on the market. With that said, it’s not easier than doing nothing. Doing nothing is very easy! Putting a boat together is worthwhile but obviously involves effort.

The current cartop to launched speed record is roughly 15 minutes. Socket the mast together. Attach the boom and stays in one go. Step the rig. Flip the boat on its side, insert the foils, right the boat, hoist the sail and launch. Complexity is best avoided.

Leaving the UFO on a dock or a beach with the rig in and the foils simply in the “up” position, achieves an ease of daily use on par with any light beach cat. To go foiling all you need to do is hoist the sail with the halyard, clip the sail to the boom and attach the downhaul line and you’re ready to launch. This brings setup and breakdown to a matter of five minutes or less.

How do I launch and land a UFO?

Far far far more easily than any other foiling boat on the market.

Because the UFO is a very small catamaran, while floating the hulls float relatively deep in the water and create lateral resistance, like the hulls on a hobie 16 or hobie wave. This means that it can sail upwind without a daggerboard of any kind in the water. This is not the case with non-catamaran foilers. The rudder is outfitted with a friction brake and a down-halyard to allow its depth to vary and allow steering in shallow water. So from 16 inches of water and beyond, you can sail away from and back to shore reliably.

Because the UFO’s forward foil assembly is located  in front of  the mast, the UFO can tack and gybe while the forward foil is fully withdrawn from the water. This is unique. It allows the UFO to navigate reliably in the period between launching or landing and flying. The benefits for usability and safety cannot be overstated.

Once you’ve got to deep enough water, lower your foils fully and fly away!

That’s if you’re using a dolly.

If you aren’t using a dolly, the UFO has even more party tricks to show off. Since the foils withdraw to above the waterline of the hull, the hull can be beached or slid up onto a dock float or boat deck without any risk to damaging the foils. The UFO is a boat that’s eager to go sailing.

Can I easily cartop a UFO?

At this hull weight, the boat is very easy to put on top of a car, and its flat bottoms allow it to be strapped down hard with no drama. The other components of the boat collapse down to the point of easily fitting in a standard hatchback.

Where can I store my UFO?

Anywhere you can carry it to. Anywhere it fits.

Behind couches, under beds, under porches, in basements, inside larger boats, chained to apartment fire escapes, hanging in garages. Anywhere it can go that’s convenient for your lifestyle is a good place for it to go.

Why does X look like Y? Surely it would be better to make it like Z.

Just trust us.

If you’ve thought of it, we’ve weighed the pros and cons and its been included or excluded for good reason. Creating a boat that can be produced at an affordable price, for a wide range of sailors with a maximum quantity of accessible performance is an extremely hard target to hit. The UFO meets all of its objectives and does so by blatantly ignoring a few conventions and norms. You simply don’t make an omelet without breaking eggs.

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• AROUND THE SAILING WORLD
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Boat of the Year 2020 F101: Best Foiler

• By Dave Reed
• Updated: December 10, 2019

At A Glance

Price As Sailed: $24,750

Design Purpose: Learn to foil, advance skills

Crew List: One or two

Rob Andrews and his ­business partner Alan Hillman have been teaching foiling for a few years now, and one thing they’ve learned is we get better by sailing, not by swimming. Thus was the genesis of the F101, a craft with which they could teach the fundamentals of foiling—without the crash and burn. But it’s not just a learn-to-foil boat, either. It’s a platform with which new and experienced converts alike can take their ­foiling skill set to a higher level.

The key to mastering the F101, Andrews explains, is grasping righting moment. With the trimaran platform, you get plenty of it, as well as a stable boat that’s more forgiving than any other small foiler. “The trimaran configuration gives you righting moment direct from the foil in the middle hull,” he says, “and gives a measure of safety. It’s hard to capsize the boat.”

The judges learn as much when it comes time to sail the F101. In 15 knots and more, and a steep Chesapeake chop, Powlison is first to give it a go. He settles into the boat, gets his bearings, perches skittishly on the weather hull, sheets on the mainsail (no need to use the boat’s gennaker above 12 knots) and off he goes like a bat out of hell, popping up on the foils without even trying.

“The trick is getting used to the sensation of heeling to windward,” he says. “It takes a bit of trust. Once foiling, it’s quiet and fast, and I felt like I had to be really active on the mainsheet to keep it on the foils.”

That’s true of any foiler, but the beauty of the F101, the judges agree, is when you do lose it, it’s no big deal. The boat drops off its foils, the bows auger in and you get a face full of water; but just reset, bear away and try again.

“The hull shape picks up the buoyancy gently,” Stewart says, “which makes it depress smoothly and prevents it from pitchpoling. When I dumped it a few times I thought I was going in, but not a chance. You quickly realize there’s plenty of floatation there to save you. In flat water, with one day of training you’d get up to speed quickly.”

When teaching people to foil, Hillman starts with “skimming,” a ride height barely above the surface. As the sailor becomes more accustomed to how the boat behaves, there’s a simple line adjustment at the foil head: Dial it up one setting and increase your ride height.

As you’re sailing, the foil wand hanging behind the trailing edge effectively feels where the boat is riding relative to the water and actuates the main flap. In light winds, it gives you more lift, and the boat pops up on the foil. Get too high, and the wand drops down even ­further, forcing negative lift on the flap, which brings you back down to your desired height and prevents the foils from breaking the surface.

In terms of construction, the judges praise its carbon-and-epoxy build quality and the all-up weight of 180 pounds, which makes it easy to get to and from the water. With the F101 sitting on its dolly in the boat park, going sailing is as simple as pulling back the covers, hoisting the main and launching from a dock, beach or boat ramp with minimal fuss.

“What I like about it is that it’s one of those boats that you buy and don’t need to add anything to it,” Allen says. “There’s ­nothing to change out or upgrade.”

For simplicity, the boat is set up with adjustments that let you ratchet up the experience as you climb the learning curve. On the rudder foil, for example, there is a clear numbering system so that as you twist the tiller extension, you change the rudder rake. The baseline setting is zero, and it’s the same for the main foil. The only thing left is to balance the forces with the mainsheet.

“When I first got up on the foils, I was thinking to myself, ‘This is too easy; I should be working harder,’ ” Powlison says. “As they said, this boat solves a lot of the problems associated with other foiling dinghies. It’s a great high-performance boat that represents the next step in making foiling accessible to the public.”

See All Winners

Other Winners:

• 2020 Boat of the Year
• Best Crossover
• Best Multihull
• Best Foiler
• Best Dinghy
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TF10 Foiling Trimaran

Ultra-modern, morrelli & melvin design, craftsmanship, wij bouwen uw nieuwe foiling boot, the tf10 trimaran: the foiling flying machine.

After the foiling revolution, the TF10 foiling trimaran is now the evolution of foiling sailing. With the TF10 foiling trimaran, sailing and foiling can be reached by any sailor. The TF10 is an 11 m long one-design foiling trimaran, designed by the famous yacht designers Morrelli & Melvin . The TF10 is built and sold by DNA Performance Sailing.

The TF10 is suitable for a crew of 4-5 persons and can handle a wide range of sailing conditions. The construction consists of pre-preg carbon fibers with a Nomex honeycomb core. This provides a lightweight, yet safe and robust construction. The foiling TF10 trimaran is the perfect foiling boat for both pleasure trips and sailing fast in races.

The transport of the TF10 is also revolutionary: when folded, it is easy to transport. We supply the TF10 with a specially designed road trailer, launching by boat ramp or crane are both possible.

Foils create sailing comfort

Thanks to the sophisticated design, every sailor feels comfortable on the TF10 foiling trimaran. Regardless of age, gender or muscle strength. And regardless of the speed, which can quickly reach up to 30 knots! Safety and comfort were the two main focuses of the design. This is reflected in a number of elements:

• The bow is designed to cut through the waves. This results in less hits on waves, which greatly increases sailing comfort.
• The carbon benches with back support provide a comfortable seat for crew and helmsman.
• The wishbone boom (half windsurfer boom) provides the decksweeper mainsail layout to perform at its best. An additional advantage is that in a manoeuvre the sail is now the lowest point and not the carbon boom.
• A ‘Semi-ridged’ carbon fibre trampoline cloth has been specially designed to make the boat’s construction torsional stiff. It makes it easier to walk on and block’s splashing water from the foils.
• The TF10’s foils and T-rudders minimize pitch and roll movements. The rake angle of all four foils is adjusted with electric actuators. This system improves comfort and safety during sailing and foiling.

TF10 hydrofoils

The TF10 foiling trimaran flies with a 4-point foil setup:

• The T-rudders with horizontal elevators generate lift and/or downforce.
• The so called Z-type daggerboard foils provide the necessary lift to be able to foil.
• The advantage of the 4-point-foil setup is that the crew does not have to pick up the daggerboards during manoeuvres. This significantly reduces the crew’s actions.
• In addition, we have electric actuators that change the position of the foils and rudders with a single push on the button.
• The design of the Z-foils has already been very successfully applied to other foiling multihulls, such as the A-cats and the Olympic Nacra 17.

Specifications

Length incl. bowsprit: 10.94 m Length waterline: 9.97 m Beam: 6.8 m Beam incl. benches: 7.65 m Beam (folded on trailer): 2.5 m Minimum draft: 0.4 m Maximum draft: 2.55 m Height center hull: 1.78 m Mast length: 16.1 m Displacement leightship: 1400 kg Displacement max. load: 1900 kg Outboard engine: 6pk, retractable Mainsail: North Sails 3Di 45 m2 Jib: North Sails 3Di 28 m2 Gennaker: (on furler) 71 m2 LED Navigation lights

Fast and pure one-design racing Easy shipping Created by owners for owners

See and feel the future of sailing. The TF10 foiling trimaran is here!

This special foiling trimaran was designed at the end of 2015. The idea was to make a foiling multihull that anybody can sail and foil with. A foiling boat equipped with the same technology as the boats at the America’s Cup.

The TF10 and its sailing class is the result of initiatives by a group of five sailing friends on the East Coast of America (Newport, RI). They have joined forces and created the TF10 sailing class.

The members of the TF10 Class Association have lot’s of experience in various one-design racing series. The goal is to create a racing series that is as exciting, honest and fun as the boat itself.

Morrelli & Melvin designed a trimaran to combine the specific characteristics of a trimaran with foiling. The trimaran’s center hull offers important advantages here: its buoyancy and pitch stability eliminate the risk of ‘nose diving’ or ‘pitch poling’. In the design briefing, wind range and sea state (short sea shipping) were important. The design of the TF10 is based on this.

For all information, competitions and the latest news, please visit the TF10 Class website: www.TF10class.com

It is possible to make a trial run with the TF10. We do this on the IJsselmeer, just a few kilometres from DNA’s shipyard. Here the sailing and foiling conditions are perfect: There is always wind and you can fully enjoy the beautiful surroundings. The IJsselmeer lies between the cities of Lelystad, Almere and Enkhuizen. The new island area “Markerwadden” can also be seen and possibly visited here. Mail us at [email protected]

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Just enjoy high speed - foiling

” iFLY – Born to FLY “

Just enjoy foiling, ” high performance sailing “, ” we love speed “, ” join the adventure “.

iFLY15 – Technical SPECS

Length 4.63 m, 15 ft..

A Foiling Catamaran for 1-2 person(s) does not need to be any longer than this. The ancient rule that says you need length to achieve speed does not apply, as hulls do not touch the water at most times.

Width 2.50 m.

This width provides plenty of righting moment, still being road legal ato be transported in horizontal position without disassembly.

7.5 m mast / 11.2 sqm mainsail

7.5 m mast with 11.2 sqm deck-sweeper mainsail. – 8.5 m mast on iFLY RAZZOR Pro with bigger rig

Draft: 95 cm

Weight: 90 kg.

90 kg ready to sail. A very light boat, providing nonetheless excellent stability for everyday suitability.

Crew 1-2 - max.180kg

Flysafe® foil control.

T-Foils Main Foils and Rudders FlySafe automatic dynamic foil control Additional Option: Main Foil Differential >>>

Know More >>>

Different - Rig Options

LATEST DEVELOPMENT OF “DECK SWEEPING” MAINSAIL THE ROLLABLE HERU WING RIG LIGHT WIND FORESAIL «CodeF»

Full Carbon Hulls

Looking for the perfect setup for your foiling sailboat.

We can recommend the best iFLY setup and accessories for your boat. Get in touch for the ultimate sailing experience!

Performance

A great number of innovations all over the catamaran and the perfect match of all components allow controlled high-speed foiling experience. iFLY15 is full of innovations, e.g. in hull design, hydrofoils, rudders, automatic flight control system, two-layer wing trampoline, high performance rig…

HULL Design

full carbon – lightweight – performance design: Born to foil

High Performance Rig Options

LATEST DEVELOPMENT OF “DECK SWEEPING” MAINSAIL WORLD PREMIERE: THE ROLLABLE HERU WING RIG : WORLD PREMIERE: LIGHT WIND FORESAIL «CodeF». ALLOWS UPWIND FOILING (as well as other courses/points) ALREADY IN EXTREMELY LIGHT BREEZE. Know More >>>

Two Layer Trampoline

AERODYNAMIC INNOVATIVE WING TRAMPOLINE CREATING LIFT.

Full Carbon T-Foils 

SCIENTIFICALLY DEVELOPED high-end foils for early take off, high speed and maximum stability.

flySafe® dynamic foil control system

The foils are controlled independently, dynamically and precisely on both sides by the flySafe® foil control system . This enables high performance sailing through stable flight. The unique foil control system of IFLY15 is a 7 years proven system developed by CEC Catamarans.        Know More >>>

IFLY MAIN FOIL DIFFERENTIAL TECHNOLOGY

MDT FOIL CONTROL – iFLY rake control The sophisticated main foil differential is an active flight assistance – The Rake is adjustable while sailing. Advanced Rake Control is for the experienced, performance-oriented Catamaran sailors / pro sailors and is a feature on the iFLY RAZZOR Pro.      Know More >>>

Innovations and more   >>>

In the hand of the experienced sailor, iFLY15 is a high-performance racing machine. STABILITY IS NOT CONTRADICTORY TO HIGH PERFORMANCE OR SPORTINESS , on the contrary, it is a prerequisite for safe reaching and maintaining constant high speeds. Stable flight allows the sailor to concentrate on the course, on the wind, as well as on opponents and strategy – rather than permanently getting distracted by working on the foiling balance.

EARLY TAKE OFF IN WINDS AS LOW AS 2Bft. / 6 KNOTS , by combining the innovative “KickOff” foil control with a trampoline that provides boost and with the latest generation of rig and foils.

BOAT SPEEDS FAR BEYOND DOUBLE WIND SPEED CAN BE ACHIEVED . Enjoy high speed foiling with top speeds far beyond 25 knots – in ideal conditions up to 30 knots.

CONTROLLED FOILING EVEN IN THE UPPER WIND RANGE BEYOND 22KNOTS OF WIND SPEED – supported by the new FlySafe® Automatic Foil System.

FOILING PLEASURE AND PERFORMANCE ALSO IN CHOPPY WATERS

FREEDOM ! FLYING SOLO OR OPTIONAL WITH CREW . You have the choice. No manhunt for crew. But still enjoy the opportunity of taking a friend or family to fly with you. Up to 140kg of crew weight. (To keep the boat and especially the mast light, we specified the iFLY15 components intentionally not for double trapeze.)

NO HOISTING AND LOWERING OF DAGGERBOARDS while sailing. (Only for beaching or in shallow waters.)

FREEDOM TO SWITCH BETWEEN FLYING MODE OR SAILING AS A CONVENTIONAL CATAMARAN (with at least the leeward hull touching the water). Within seconds iFLY15 can be switched to Non-Flight mode, even while sailing. In that mode, iFLY15 will not take off, but the foils will still create lift and give an extra agile sailing behavior, which is on the same time very stable as rudder Foils will avoid pitch poling. Non-Flight mode is providing additional security in extreme high wind speeds. It is also useful for less experienced sailors or in all situations, where taking off is undesirable (e.g. in the harbor or while towing…).

EASY TO LEARN FLYING BY AVERAGE SKILLED AND TRAINED SAILORS

EASY BEACHING AND SLIPPING , as simple as with any conventional beach catamaran by using a standard catamaran beach trolley. Foils remain flat under the keel, with the daggerboard lifted as on a conventional catamaran.

SIMPLE TO DISASSEMBLE PLATFORM . Width of 2.50m is also road legal in most countries for horizontal transport without disassembly.

DAGGERBOARDS CAN BE PLUGGED IN FROM ABOVE and Foils securely anchored from below with one central screw.

FAST SET-UP OF THE iFLY15 FROM ROAD TRAILER TO SAILING . Simple rigging the mast, no genacker boom, no foresail, no spi.

SILENT AND CALM PLANING ABOVE THE WAVES . Flight height of up to 90cm, avoiding even high waves below.

EASY TO FOIL THE JIBE (without landing). Stable maneuvers are made easier by the fact that the four T-Foils always remain in the water.

« INTERNATIONAL FORMULA 15 FOIL » Class Association. The new development class for FOILING, SINGLE HANDED on MULTIHULLS. Multi manufacturer class in the tradition of a Formula18, A-Class or international Moth. Enables large regatta fields and evolution of the boats, following the technical progress (which is especially essential in the case in Foiling). Strict regulations to avoid uncontrolled exaggerated development.

Contact : [email protected]

Catamaran Europe Central

The iflysail team, is looking forward to your message, more to know about ifly foiling , interesting tech, high performance rig options >>>, flysafe® dynamic foil control system >>>, ifly main foil differential technology >>>.

MDT FOIL CONTROL – iFLY rake control

News and More

Ifly foiling experience >>>, press articles >>>, events >>>.

High-Performance Foils

Shaping better centerboards and rudders

From Issue   July 2020

W hile it’s generally accepted that the right sails and sail trim will determine how close you can sail to the apparent wind, a sailboat’s progress to windward also depends on the lift and drag generated by the centerboard and rudder. How much difference does proper foil shape make over a simple rounded leading edge and tapered trailing edge, anyway?  Foils operating in fluids, whether air or water, are a well-studied topic. C.A. Marchaj, in his book, Sailing Theory and Practice , discusses the theory and gives the results of actual tests of differences in foil planform (side view), cross-section shape, size, and aspect ratio (AR – length to width). Lacking other constraints, an ideal centerboard, daggerboard, or rudder blade should have a reasonably high AR (greater than 2) planform with a streamlined cross-section that has a parabolic leading edge and a thickness of somewhere near 10 percent of the chord width (the distance from leading edge to trailing edge). A thickness of 8 percent produces less drag but stalls sooner; 12 percent has a higher stall angle but produces more drag.

Exactly where the point of maximum thickness should be located is a matter of some debate. Marchaj suggests it should be at 50 percent of the chord width, halfway between the leading edge and trailing edge, but provides no data to back that up. Other sources suggest that the NACA (National Advisory Committee on Aeronautics) symmetric foil sections, originally developed during aircraft research, are actually a good fit for boat foils operating at low speeds in water. A NACA 0010 foil, for example, has a maximum thickness of 10 percent of the width of the foil, located at 30 percent from the leading edge.

Of course, there are many practical reasons why not all keels, centerboards, and rudders have high AR planforms, but the cross section for a foil of any planform should be streamlined. My personal experience of doing it wrong on one boat, and getting it right on another boat, has convinced me that the NACA sections and guidelines above provide good performance.

HORNPIPE, my first sail-and-oar boat, was an 18’ Kurylko Alaska with a standing-lug ketch rig, and sailed well enough to windward in flat water, but lost 10 to 15 degrees of pointing ability as soon as the water got choppy. I knew it wasn’t poor sail trim. Eventually I got looking at the daggerboard and analyzed it. It was only about 2.5 percent of the sail area and its thickness was only about 6 percent of the chord width, neither big enough or thick enough in my view, and in rough water it lost laminar flow and lift. When I designed my 18′ lug-yawl cruiser, FIRE-DRAKE, I gave it a thicker centerboard with a greater fraction of the sail area, about 4 percent. I also gave it a straight quarter chord line (think of the shape of the wing of a Spitfire aircraft) and a moderately high aspect ratio of about 3:1 for the planform area. To get the daggerboard foil shaped accurately and quickly I opted to have it cut on a computer numerical control (CNC) machine. All that was left for me to do was sand, seal and paint, and make an epoxy-lined hole for the pivot pin.

The results have been what I had hoped for. FIRE-DRAKE sails quite well to windward and maintains its performance in rough water. I sailed in the company of a similar boat—with the same length and beam, the same weight, and the same sail plan—along the south half of the Inside Passage, and that boat’s centerboard was shaped by eye. When sailing to windward, FIRE-DRAKE would consistently point higher and walk away in speed. My centerboard even let me continue sailing to windward when my partner gave up and took to the oars.

Although I had the daggerboard shaped with a CNC router, it is possible to shape a high aspect ratio, fully streamlined foil in the home shop. I’ll walk you through my second project, a kick-up rudder blade that I made at home to replace the original one I built for FIRE-DRAKE. I settled on a planform that is one-quarter of an ellipse with an elliptical leading edge and a straight trailing edge. (The shape would move the center of lateral resistance of the boat aft a few inches, and is intended to lighten the weather helm I’d experienced with the original rubber blade.) I drew the new blade with an aspect ratio of 2.5:1, with a length of 30″ (762 mm) and a maximum chord width of 12″ (305 mm), which would increase the lift and reduce the tip vortex drag.

To draw the planform shape of the quarter ellipse you can use an online graphing tool such as Desmos for a full ellipse. If you center the ellipse at zero, you can drag the two axes out until you get the aspect ratio you want. Since the graph has a grid in the background, you can then print out a screen capture of a quarter of the resulting ellipse and scale up the printed image to the actual dimensions required. If you are comfortable with computers, you can download and run Freeship (available for Windows only) which has a “keel and rudder wizard” that accurately generates several different planforms.

The new rudder blade for FIRE-DRAKE has a quarter-ellipse planform. The plywood’s glue lines show the contours that help with shaping the foil.

Obtaining the cross-section profile of a chord of a given width is best left to a computer. For any of the NACA foils, like the 0010 foil I mentioned above, Competition Composites Inc . (CCI) has a very simple and handy calculator . You need enter only the chord width and the maximum thickness and it will generate a table of X-Y coordinates that you can copy and print out. They’ll be your offsets for drawing a pattern for the foil cross-section. If you intend to sheathe your foil with ’glass and epoxy, for example, you can also enter the skin thickness and it will calculate the coordinates for the plywood core.

Now, here’s the tricky bit. If you have a rectangular foil planform, you only have one chord width and therefore one section profile for the entire length of the foil. However, if you have any other planform (e.g., half-ellipse, quarter-ellipse, trapezoidal, straight-chord-quarter-line, etc.), the thickness, which will be one-tenth of the chord width, changes along the length of the foil because the chord width changes.

I used the CCI calculator to generate profile coordinates for three different points along the length of the rudder blade: at the root, at about two-thirds of the way along and at about 90 percent of the way to the end. I chose those points because the chord width for my quarter ellipse planform doesn’t change much for the first half of its length, but it changes more quickly toward the tip. The idea is to shape the foil to these profiles at these points and then taper the foil evenly between them. You can lay out your foil plan directly on to the ply or you can use something thin, like doorskin, to make and fine-tune a template, which is what I did.

I made a blank for my rudder by gluing layers of marine ply with epoxy to the required 1″ thickness. I have found that the plywood, in spite of its cross-grain plies, has sufficient strength for the size of small-boat foils that I have built (though the cross-grain would weaken a long thin foil). Plywood does not warp and has the added advantage over solid wood in that the plies create a kind of contour map that give you graphic visual feedback as to the evenness of your surface once you start shaping the foil. You can make a foil with solid wood or even foam plus a ’glass-and-epoxy skin, but without the plywood laminates as guides, you would have to make more section profile templates to ensure a smooth and accurate shape.

Clamping a 4′ level to the flat part of the rudder blade provides a reference line to gauge how much wood to remove to achieve the foil’s taper.

The next step is to taper the thickness of the laminated foil blank along its full length. Knowing the required thickness at your chosen points, you can draw a pattern for the curve of the taper and half the thickness of the blade stock and measure how much wood you have to remove at each point. I clamped my 4′ aluminum I-beam level to the flat part of the rudder blade above the shaped part, and used a ruler to measure the depth I had to cut to. To remove the wood for this part of the project, I used my #4 Stanley plane. While I have a power hand planer, I didn’t trust myself with it to not take too much off too quickly.

The female half-section template for a given chord for a foil gets its shape from the X-Y coordinates generated by a foil calculator.

I made three female half-section profile templates, one for each of the three points noted above, by plotting out the generated X-Y coordinates on pieces of doorskin and carefully cutting them out. One thing to note is that the CCI calculator generates a profile that has a trailing edge of zero thickness. Obviously, this is not practical to build in wood, and a knife edge is not that critical anyway. I adjusted the trailing edges so that the finished edge would end up about 1/3″ (4mm) thick.

Applying the template to the foil in the works shows the high and low spots as the shaping continues.

Next, I used the profile templates to shape the foil at my three chosen points. I shaped the plywood with a Shinto rasp , regular rasps, and coarse sandpaper. It’s a process of taking some wood off, placing the template, and repeating until you get the section of wood shaped to the templates. Once that is done, I could go to work taking down the wood between the sections, using the ply layers as a guide. I used my block plane, Shinto rasp, and sandpaper for this task. I eyeballed a smooth transition around the tip from the leading edge to the trailing edge.

I sealed the surface of the shaped foil with a couple of coats of epoxy to provide a smooth, hard surface to accept a finish coat of marine epoxy enamel.

Alex Zimmerman is a semi-retired mechanical technologist and former executive. His first boat was an abandoned Chestnut canoe that he fixed up as a teenager and paddled on the waterways of eastern Manitoba and northwestern Ontario. He started his professional career as a maritime engineer in the Canadian Navy, and that triggered his interest in sailing. He didn’t get back into boatbuilding until he moved back to Vancouver Island in the ’90s, where he built a number of sea kayaks that he used to explore the coast. He built his first sail-and-oar boat in the early 2000s and completed his most recent one in 2016. He says he can stop building boats anytime. He is the author of the recently published book, Becoming Coastal .

For further reading on the pros and cons of the variables in foil design, Competition Composites (CCI) has a good discussion . For those of you who want to go into the math, Paul Zander has a good presentation from nearly 20 years ago, and also, for those inclined that way, an updated discussion with a lot more math.

You can share your tips and tricks of the trade with other Small Boats Magazine readers by sending us an email .

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Comments (17)

Is there someone who can craft a good rudder for my boat? I have not the time or the skills to do such. Have a 15′ Delaware Ducker. Love the boat but the rudder is (I think) a disaster. Hardly brings the boat around and doesn’t help much to windward. Flat plywood barn door out of 3/8″ ply with no shape other than outline that barely gets 2″ – 3″ into the water. If it could be a kick-up so much the better. I do a lot of shallow, sand-bottom sailing. Thank you for any help.

I know about the ducker and a foil shaped rudder will help a lot. Some of the modern ones built in glass and cold molded have been fitted with modern dinghy rudders and foil shaped daggerboards. They tack more like a dinghy than like my traditional one where I have to sail it around like a larger boat.

Most any small boat builder in your area should be able to build you a rudder. Lines for a kick up would be a nuisance. I don’t bother with them on a larger boat, just use a pivot bolt with tension. Means I have to shove it down.

You might want to look at the system that Mike Storer has developed for his goat island skiff, a straight foil, easier to shape.

Alex has done a great idea showing us how to work these out using hand tools. We used to do it in my dinghy sailing days by drawing a 30 % line. Make a bunch of parabola templates and hack away. For really long narrow boards before the days of carbon we used to use 5/4 stair tread fir.

Interesting article. When I built my Oughtred JII Yawl eighteen years ago, I did some research on appropriate foil profiles for the centerboard and rudder. It’s a long time ago now, so I don’t remember the exact profiles I chose, but I do believe I picked NACA 0010 for the CB. I picked another profile for the rudder, one that had a steeper stall angle, on the theory that with typical weather helm the rudder meets the flow at a steeper angle than the CB. I really don’t know how valid my theory is. I have no experimental evidence to back it up. Any thoughts?

Andrew, that seems to make sense although I haven’t seen any research to back that up.

Hi Andrew, I remember seeing your beautiful JII; but did not ask about the foils! I wonder how NACA 0010 compares with my approximate foil shape, inspired mainly by guesswork. Are these profiles available? By the way, I do not like plywood foils; CBs break. Friends near here lost their fine old rebuilt Wayfarer; were in danger themselves, when they capsized and the plywood board broke. Too near a rugged lee shore. A class racing boat, by a particular builder – all their plywood centerboards broke.

Iain, I don’t know what your standard foil shape looks like, but a NACA 0010 has a maximum thickness of 10% of the chord distance, occurring at 30% of the distance back from the leading edge. Marchaj believes that the maximum thickness should occur at about 50% of the distance back from the leading edge. Other designers agree, I think. If I understand him correctly, John Welsford uses a foil section that is closer to 50% distance, but I am not sure what thickness of foils he favors or what the exact foil shape is. You can see the shape, and all the requisite numbers for extracting an X-Y plot to reproduce them, for a whole bunch of different foil types, on the Airfoil Tools site. As for plywood foils, I understand your concern. Half the plies are oriented in the wrong direction and don’t provide much in the way of resisting sideways bending moments. However, it has been my experience that this is not a major concern if the foil is thick enough and not too long. The centerboard foil on my latest boat, for example, is ply, but is nearly 2″ (50 mm) at maximum thickness. It’s got over 1,000 nautical miles in four years under the keel by now, including a couple of practice capsizes, with no issues so far.

I don’t know what a standard Wayfarer foil looks like. Is it long and thin?

Very interesting article. I am just in the process of building a Lillistone Flint and have no experience building or knowledge of foil design and performance. I calculated the various ratios and percentages. The AR as per the plans is 2.43, so that looks good. The thickness however is only 4% of chord width. Area of the dagger board is 3.5% of sail area, so probably OK there too. Lillistone does state in the plans that the board can be made thicker if preferred so I think I may do that as 4% is a pretty big departure from the 8 – 10% of the chord width suggested. Any comments? The Flint was featured in this mag a few issues ago.

David, both my experience and authorities who design for a living and/or who have tested these things would suggest that 4% is rather too thin for good lift. I suspect that you might find it works reasonably well in dead flat water but you would lose lift and pointing ability as the water gets more turbulent. If it was me, and I hadn’t yet built the foil and its case, I’d go for one that was at least 10% and maybe even 12%. The additional thickness would also be more robust should you need to stand on it to flip the boat over if you capsize.

Thanks so much for taking the time to reply, Alex. I have decided to use some salvaged King William (King Billy here in Tasmania) pine that was salvaged. I thicknessed it to clean it up a bit and reckon I will eventually get 20 – 22 mm out of it. I plan to laminate 10 pieces into a 304mm board. Hopefully I will get a good result.

Hi David, It highly depends where you sail and how you sail. I have one older (1975) 420er dinghy for fun and local competitions with foiled board and rudder. But then I have 21″ German Jollenkreuzer veteran from 1952 which has both from 1/4″ steel plate, and it works fine. I sail that for pleasure on lakes. It would definitely be more performant (and point better) with both foiled, but I’m surprised how well it performs in its nearly ’70s (comparing to modern GRP boats with foiled boards).

For your job, I would probably stick to the plans. The rudder in this case is more important and can be somehow easily modified (foil). The centerboard I would keep the same, not only to conform the centerboard box (which would need to be sized), but also the overall design. Finally the most important here is what is your building and designing experience, because the worst thing is when something is incorrectly designed and then improperly built (the simple rounded plywood then may work better).

Anyway, I’m also thankful for this article. It reminds me my childhood when I built airplane models and used exactly the same methods used here to create the wings (in much smaller scale).

Thanks for your thoughts. I am going for a thicker foil and risk it (see reply to Alex above). I am well aware of risks in departing from designer’s work but I don’t think I will go far wrong.

Do SUP fins follow the rules for centerboards?

I’m not a SUP guy myself, but my understanding is that the fins are there to assist in tracking. That is, they don’t need to provide lift the way a sailboat keel/CB going to windward does. The thing you would be aiming for in the case of SUP fins is having sufficient lateral area to provide that tracking ability, and then having it streamlined to reduce drag. I would imagine that thinner would be better, although you’d still want a streamlined foil section, as that would produce less drag than a flat plate. The leading edge of a flat plate tends to separate the flow from the sides of the plate, even if that edge is rounded, and separation produces turbulence and drag.

For twenty years, beginning in the early 1970’s, I raced a Lido 14. The boat was pre-owned, and had its original solid wood foils which were in pretty bad shape, and I decided to build new foils. After reading Marchaj’s book, and the Lido 14 Class Rules, I designed a new centerboard and rudder. The NACA-0009 section most closely fit the required class measurements, and I used that profile. I did alter the leading edge of the rudder, making it more rounded, to allow for the fact that the rudder angle of attack is variable, and is more likely to stall.

In fleet racing, and sailing close hauled, the results were astounding, with the boat seeming to sail slightly sideways, relative to other boats. I also began to pay particular attention to the condition of the foil surfaces, as Marchaj writes that the drag on underwater foils is many times greater than the drag on the hull surface. One time we were sailing in an area of submerged trees, and my centerboard lightly brushed a tree branch. I then noticed that the centerboard ‘hummed’ on port tack. Later, when I examined to board, there was a barely visible scratch.

I very much enjoyed the article on high-performance foils in the July 2020 issue of the Small Boat Magazine .

For twenty years, beginning in the early 1970’s, I raced a Lido 14. The boat was pre-owned, and had its original solid wood foils which were in pretty bad shape, and I decided to build new foils. After reading Marchaj’s book, and the Lido 14 Class Rules, I designed a new centerboard, and rudder. The NACA-0009 section most closely fit the required class measurements, and I used that profile. I did alter the leading edge of the rudder, making it more rounded, to allow for the fact that the rudder angle of attack is variable, and is more likely to stall.

In fleet racing, and sailing close hauled, the results were astounding, with the boat seeming to sail slightly sideways to windward, relative to other boats. The boat didn’t seem to point higher, when close hauled, it just didn’t make as much lee way. More benefit on the port tack, a little less on starboard. I did set the centerboard jibe angle to the maximum allowed by class rules. In all honesty, I was probably the only one in the fleet that had read Marchaj. It still took me five years to win the fleet championship. I also began to pay particular attention to the condition of the foil surfaces, as Marchaj writes that the drag on underwater foils is many times greater than the drag on the hull surface. One time we were sailing in an area of submerged trees, and my centerboard lightly brushed a tree branch. I then noticed that the centerboard ‘hummed’ on port tack. Later, when I examined to board, there was a barely visible scratch.

I am a new subscriber to Small Boat Magazine , and look forward to each issue. Keep up the good work.

Was just about to make the centerboard for my Oughted Caledonia Yawl. So I was happy to see this article. But was then disappointed when I calculated my centerboard area to be only 1.9 percent of my total sail area. I briefly thought gee I will make it a little bigger…but then realized the centerboard trunk is already complete and limits that. I don’t plan on racing, so it is what it is.

Mark, I’d be really interested in your results once you launch the boat and do some trials. Theory is one thing, but nothing beats data from real-world results.

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From the designers of the Persico 69F, the MW40OF is an offshore racer with full foiling capabilities packed into a manageable size and capable of normal docking without issues from foils sticking out and with safety and simplicity as driving factors.

Thought for a crew of 5, the concept is 40ft LOA and is equipped with fully retractable round foils, canting keel and twin rudders with elevators.

The whole process that went on designing and developing the 69F allowed us to confirm theory with practice in different aspects of the still evolving foiling ground and monohull foiling in particular. Despite the boat did everything that was planned her to do and outperformed expectations, it’s in the details and on the water where you bring up a great deal of confidence to take steps in new directions.

An offshore racer with full foiling capabilities, at a manageable size and capable of docking normally was an idea always around. Naturally we imagine to race such a boat in coastal offshore races we have at hand at our land home but of course the idea goes beyond and with some potential clients that could be interested in such a concept we thought to do a first design loop around such premises.

Putting all pieces together to come up with something that fulfil the goals you impose to is always a challenge but such a premise falls short when speaking about a foiling vessel.

While the concept may seem straight forward in this foiling era, there are plenty of constraints that quickly set some clear limits. It is the usual short blanket problem as you will want to cope with several aspects: Foiling Performance, Floating Performance, Static Stability requirements and last but not least a handful of practical issues to sort out.

You cannot cover all aspects in an ideal way and they sometimes work against each other, so you must choose priorities and find some balance to make the concept work.

A relatively small boat helps on the foiling side due to its better power to weight ratio, but not so much on stability requirements as a smaller boat and greater beam/length ratios means heavier bulb weights to meet static stability requirements. So, after some initial studies a 40ft seemed a good compromise to start with and from where concept could grow or shrink depending on client needs and/or further developments.

Foil & Keel must be thought as working together. Configuration needs to maximize foiling capacity, fulfil docking requirements but also promote transverse stability on flight. On top of that it must not compromise non-foiling conditions too much.

One of our driving goals had dynamic transverse stability on flight as in the end means how easy the boat will be to keep foiling through changes on wind strength or waves which is particularly important in a boat that takes the most from high average speeds more than top speeds as is the case of offshore and long-distance coastal races.

The very first big choice is the option to have a fixed keel instead of a canting keel. This allows you to have a lighter boat to fulfil static stability requirements. But although that looks very tempting on paper, it might compromise dynamic stability of the boat in any other than smooth, flat water conditions due to the lack of upward force exerted by a fix keel at normal heel angles. On top of that the canted keel also helps pushing the boat out earlier despite being a slightly heavier boat. So, a canting keel system oriented to this particular use still seems to be a good compromise.

Foil configuration itself is pretty natural when thinking on a dock-able boat, with a fully retractable round foil being the way to go. But this foil geometry also makes sense with a boat that will always work with some heel to conform a double point support together with the keel at the front. This type of foil is relatively shallow and needs the heel of the boat to maximize its action. It also has the additional benefit of allowing complete removal on light wind conditions. Then a retractable double rudder set up stands up natural too with leeward rudder matching perfectly with heel and increasing righting moment.

Performance

Initial VPP studies show reaching and downwind foiling points already at 12kt TWS with boat speeds between 19kt and 30kt across normal wind range. There is also potential upwind foiling with TWS above 15kt yet with full use of the foil in winds above 10kts in what is usually called semi foiling or skimming modes with TWA in the range of 65-75. Further work will be carried out for an optimization of the rig and sail wardrobe towards defining final VPP figures and sail crossovers.

A double wheel was chosen to steer smooth and firm, integrated to the cockpit seats to save space. All running rigging is centralized around the back of the cabin as usual on offshore boats with a central pit and winches on the sides. Traveler track at the back made sense as its own bridge will conform part of rudders support structure and make for a safe cockpit enclosure. Also, room for a coffee grinder will be necessary to allow quick trimming of the mainsail when foiling although the details has yet to be developed as rig power management is crucial for a steady flight. An offshore styled type of cabin intends to cover the crew as much as reasonably possible completes the general exterior look.

A standard two spreader mast that stays inside the beam of the boat (no outriggers nor rotating mast) made sense to keep things simple and docking of the boat standard. Room for deck poles to optimize Code 0 type sails size and sheeting angles it’s on the plan in order to optimize both foiling and floating polars.

For more information and/or request of a bidding package please contact with  [email protected]

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Monofoil: The pocket rocket that can foil in just 8 knots of breeze

• Matthew Sheahan
• October 1, 2019

Built and developed in secret, the 8m Monofoil is a super-fast one-off foiling monohull, originally designed as a lake racer

The spectacle of a flying catamaran, be it an Olympic Nacra 17, a GC32, the recent America’s Cup 50-footers, or anything in between, has become almost normal in today’s racing world, so rapid has the shift to foiling been among multihulls.

But, even 17 years after they first appeared, the sight of a diminutive foiling Moth still turns heads. Foilers don’t have to be big to be impressive, balancing a single hull on a single foil is enough. Like those who can ride a unicycle, there’s something awe-inspiring about watching sailors who have pitch perfect balance fly a twitchy monohull while making it look like the most natural thing in the world.

There have been plenty of attempts to bring monohull foiling to bigger boats and to the masses. Yet no one has yet cracked the code, at least not for production boats.

Little surprise then, that whenever a new monohull foiler comes onto the scene it attracts plenty of attention. One of the latest is the 8m Swiss-built Monofoil. This extraordinary and complex looking boat is essentially a sportsboat with an open cockpit but with outrigger foils, like bicycle stabilisers, that generate righting moment by pushing upwards on the leeward side.

She was designed by Swiss match racing sailor Eric Monnin and built by Damian Weiss, both of whom shared a common goal: to create a fast foiling monohull for the European lakes.

Interestingly, neither had any desire to create a production version, nor tell the world that this was the answer for others. Instead, they simply wanted to find out if they could fly fast enough on one hull to stand a chance of winning some of the big prizes at Europe’s top lake races, including the famous Bol D’Or Mirabaud.

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Launched in the spring of 2018 after two years of secret development, the initial signs looked good as the 8m sportsboat delivered an impressive opening performance, topping 25 knots on one of her first outings.

After a winter of tweaking and refining, where the team had increased the foils by 20% and reduced her overall weight by 50kg, the Monofoil was back afloat for this season. Shortly after her re-launch at Easter, it was clear that the team had raised the game.

“We can now foil upwind in just 8 knots of breeze,” said Monnin. “And when the breeze builds to 12 knots we are travelling at 16-20 knots at a true wind angle of around 50-60°. When it comes to downwind performance we can happily sit at 22 knots in 12 knots of wind with the gennaker. After that, when the breeze is up to 15-20 we are holding 24-27 knots with just the main and jib,” he continued.

The carbon bowsprit is 1.2m long and cants so the tack of the gennaker can be set further to windward, allowing the Monofoil to sail deeper

All impressive stuff for an 8m monohull. This is a proper pocket rocket that weighs just 650kg and can be rigged off the road trailer and launched in a couple of hours. Indeed, Monnin explains, her performance was in part limited by the need to keep the maximum beam down to 2.5m to meet European towing regulations.

Single hull foiling

So how does the Monofoil work? Setting the foils to one side to start with, the 8m long sportsboat flies a self-tacking jib upwind and a gennaker off a canting bowsprit downwind. She is designed to be raced by a full crew of four, including the helmsman, with two on trapezes to boost the righting moment.

She has a large square-topped mainsail that makes full use of the available space in a sail plan that sees the boom extend all the way to the transom where a full width traveller allows plenty of mainsheet tension to keep the head of the main stand up. This does mean she has a pair of running backstays rather than a single fixed stay, but double aft swept spreaders provide sufficient fore and aft support for the mast.

The foil deployed, but in the raised position. Normally it wouldn’t be underwater but the boat was heeled at the dock

Being a potent performer, she sails at high apparent wind speeds with the apparent wind ahead of the beam. This makes the full width mainsheet traveller an important feature to allow the mainsail to be dropped down to leeward while still maintaining leech tension, much like a multihull.

Her rudder is mounted on a transom-hung gantry to ensure greater efficiency for the T-foil blade. The rake of the rudder can be adjusted to alter the fore and aft trim of the boat.

While the foils look large and complex, their operation is surprisingly simple and belie the amount of work that has gone into designing a complete system that allows the curved foils to slide through a set of bearings in the hull.

A simple rope-driven worm drive alters the rake of the T-foil rudder, which in turn alters the trim of the boat. The rudder is mounted on a gantry off the transom to minimise cavitation

Much like the Beneteau Figaro 3, the idea is that both boards are lowered when sailing. Yet unlike the Figaro, the windward board is lifted partially to help raise it above the water’s surface and reduce the chances of it becoming immersed where it would create drag.

The clever part is the small amount of movement that is required to lift and lower the boards, especially when compared to the amount of movement required to raise and lower daggerboards on a modern multihull.

Also unlike the Figaro, the Monofoil’s boards are fully retracted in light winds. With very little of the foil in the water there is minimal drag and the boat can be sailed like any other monohull.

A custom bearing lets the daggerboard slide vertically to be raised or lowered. Rake is adjusted by the green line winding a worm drive

In these conditions the skinny and efficient 2.2m deep keel, with its 160kg bulb, is a good combination when the breeze is below 8 knots and allows the Monofoil to perform like any other similarly sized sportsboat.

The dihedral (upwards angle) of the foils is also an interesting feature that provides a degree of automatic heel control. As the boat accelerates and comes upright, so less of the foil is in the water, which reduces vertical lift.

Deceptively simple

At rest this boat does look pretty complex, yet once she’s rigged and underway you realise how simple she is to operate as well as how much effort has gone into designing her that way.

Below decks the full carbon construction is clear to see

This is an ingenious trailer-sailer that will fly in light conditions and be stable on foils right up through the wind range, something the crew demonstrated during this year’s Mirabaud Bol d’Or. As a vicious 50-plus knot storm swept through the fleet, she and her crew were one of the few to survive unscathed and go on to complete the overnight race.

The irony remains that – unlike many others in the Bol d’Or – this is not a boat that was intended to be the prototype for a new range of production foilers, even though she appears to provide answers to plenty of questions.

The bottom line is that the Monofoil seems to work. Irrespective of what speeds she clocks up, what is most impressive is how she performs across such a wide range of wind speeds.

Rectangular cut-outs in the hull allow the foil to be lowered completely on the leeward side. The windward foil is raised slightly in a similar way to pulling up a normal daggerboard

The Monofoil is no one-trick pony and while the concept wasn’t created for production, it could provide an appealing route for those who are realistic about their ability to learn how to balance like a Moth sailor, or ride a unicycle.

Specification

LOA: 8.0m (26ft 3in) Beam: 2.5m (8ft 2in) Displacement (empty): 850kg (1,874lb) Mast height: 12.2m (40ft 0in) Mainsail area: 32m 2 (345ft 2 ) Headsail area: 16m 2 (172ft 2 ) Gennaker area: 50m 2 (538ft 2 )

Discover the Magic of Hydrofoil Sailboats

Last Updated by

Daniel Wade

December 11, 2023

‍ Key Takeaways

• Hydrofoil sailboats blend speed, stability, and innovation for a fun sailing experience.
• Their design lifts the hull above water, reducing drag and enabling high-speed travel.
• Advanced control mechanisms maintain stability in varying wind conditions.
• Sails and hulls are meticulously engineered for optimal aerodynamics and lift.
• Ongoing innovations in foil technology continue to propel hydrofoils to new heights.

‍ Based on their innovation and nature, the world of hydrofoil sailboats are magical, to say the least. But what exactly makes them so exceptional?

The magic of hydrofoil sailboats lies in their extraordinary speed. They can achieve remarkable speeds that were once thought impossible for sailboats. Their unrivaled stability and cutting-edge technology redefine sailing, offering a thrilling blend of innovation and performance.

Over the years, I've dedicated myself to mastering the intricacies of the yachting world, not just as an observer but as an active participant in the hydrofoil sailing community. My knowledge extends beyond the surface, encompassing the technical aspects of hydrofoil design and the thrill of high-speed sailing. As such, I’ll provide a comprehensive and engaging exploration of what sets hydrofoil sailboats apart, making them truly magical on the waters.

Table of contents

‍ Discover the Magic of Hydrofoil Sailboats

Hydrofoils saw their early development as a concept for enhancing speed and efficiency on the water. From Alexander Graham Bell's experiments to the application of foils on sailboats in the 1950s, the quest has always been for greater speed.

But it wasn't until Russell Long championed these designs with the CEC foiling catamaran and the development of the Hobie Trifoiler that hydrofoils began to carve a distinct niche in the sailing world.

This sailboat operates on a simple yet ingenious principle: as the speed increases, the foils submerged beneath the boat generate lift. This lift thrusts the boat's hull above the water, dramatically reducing drag.

It’s similar to how air flows around the wing of an airplane, only with water's denser environment offering a different dynamic. This revolutionary foiling system allows boats to glide over waves, offering an incredibly smooth ride.

The variety of hydrofoil sailboats is astounding, from the foiling catamarans that have revolutionized the America's Cup to the twin sail trimaran designs. The fastest production sailboat, the Hobie Trifoiler , showcases what hydrofoils are capable of.

Additionally, boats like the innovative Emirates Team New Zealand vessels continue to push the boundaries of technology in competitive sailing. Whether for recreational purposes or high-speed racing, the range of hydrofoil sailboats caters to different sailing experiences and preferences.

Now, let’s explore the various aspects of hydrofoil sailboats that make them truly magical.

The Thrills of Hydrofoil Sailing

When I first stepped onto a hydrofoil sailboat, I knew that sailing would never be the same for me. Harnessing the power of the wind to achieve remarkable speeds while hovering above the water was nothing short of revolutionary.

It's an adrenaline-infused blend of sailing, flying, and innovation that promises high performance and stability with a significant reduction in wetted areas.

The allure of hydrofoiling is not just about the speed; it's the sensation of flying over the waves, defying the conventions of traditional sailing. With each gust, my hydrofoil sailboat becomes a silent, swift car, slicing through the air rather than merely sailing on the water.

When sailing with hydrofoils, you get to experience the following benefits.

• High Speed: With hydrofoils, I've seen and achieved speeds I never thought possible on water.
• Less Wetted Area: As the hydrofoils lift the hull out of the water, drag is reduced, further contributing to the craft's efficiency and speed.
• Stability: Surprisingly, the flying sensation is accompanied by stability once airborne, making the ride smoother.

The America’s Cup Competitive Foiling

Over the years, I've witnessed first-hand how hydrofoil technology has radically altered the landscape of competitive sailing. The introduction of hydrofoils has not only redefined what we consider possible in the sail area but has also brought a fresh surge of excitement to the racing circuit.

The most illustrious event in sailing, the America's Cup , underwent a transformation with the embrace of hydrofoils. Emirates Team New Zealand, a frontrunner in hydrofoil innovation, redefined the America's Cup racing in 2017.

Alongside them, the US team and Luna Rossa played pivotal roles in reshaping the landscape of America's Cup racing.

With their AC50 class catamarans soaring above the waves at top speeds that defy traditional sailing limits, they clinched the title and shifted the focus of competitive racing toward technological prowess.

The spectacle of these vessels racing is not just about the crew's capabilities but equally a testament to engineering marvels.

Also, the advent of hydrofoils in racing has certainly led to a spike in performance metrics. Here's a concise table highlighting the before and after impact of hydrofoiling in competitive Sailing:

This table illustrates just how much the racing landscape has shifted; it's not only sailing anymore.

It’s similar to piloting a high-speed aircraft, with each crew member playing a crucial role in harnessing the raw power of the strong winds in harmony with state-of-the-art technology. Watch this video for a more detailed explanation of hydrofoil sailboats and their magical power.

Technical Aspects of Hydrofoil Sailboats

In diving into the technical aspects of hydrofoil sailboats, I'll give you an insight into the intricate designs that enable these marvels to glide above the water, as well as the cutting-edge foil technology propelling them.

The design of a hydrofoil sailboat revolves around its capability to elevate the hull above the water, reducing drag and enabling high wind-speed travel. Control mechanisms are central in maintaining stability, especially when the sailboat interacts with varying wind conditions or maneuvers through shallow waters.

The hull's length and overall design are calibrated for balancing aerodynamics with hydrodynamics. In designing sails and hulls for foiling, one must carefully balance the need for power with the propensity for lift.

The sails are tailored not only to harness the wind's energy effectively but also to match the unique mechanics of a vessel in flight. Meticulous engineering ensures that the sail configuration works in harmony with the foils to propel the sailboat forward swiftly.

Additionally, the foil technology, which is pivotal to modern hydrofoils, has undergone significant further development over the years . From the materials used to the manufacturing processes, every element incorporates the latest in technology to yield extreme performance.

Advancements have led to foils that can automatically adjust to sailing conditions and speed, which is instrumental for achieving and maintaining high speeds.

Currently, the future of hydrofoil technology seems bound for even further breakthroughs. Customization and refinement of foils for specific water conditions, such as the challenges posed by shallow water, are ongoing.

Each new iteration builds upon the last, consistently advancing the field and informing the next leap in hydrofoil sailing. This persistent innovation in foil and hull technology is a testament to the potential that lies ahead for hydrofoil sailboats.

Are Hydrofoil Sailboats the Right Options for You?

Hydrofoil sailboats offer a unique and thrilling sailing experience, but whether they are the right option depends on your preferences and goals. These high-performance vessels are known for their exceptional speed and stability, making them ideal for thrill-seekers and competitive sailors.

If you're passionate about cutting-edge technology and want to push the boundaries of traditional sailing, hydrofoil sailboats could be a perfect fit.

However, they may require a learning curve for beginners and are typically more expensive than traditional sailboats.

Consider your skill level, budget, and desire for speed and innovation when deciding if hydrofoil sailboats align with your sailing aspirations.

The Future of Hydrofoil Sailboats and Their Transformative Potential

Over the years, I've been captivated by the evolution of sailing and the recent advancements in hydrofoil technology, which promise a thrilling future for these marine crafts.

The technology supporting hydrofoil sailboats is rapidly advancing, bringing us closer to a world where boats gliding above the water's surface is a common sight.

These boats use 'wings' or foils submerged in water to lift the hull above the surface, reducing drag and allowing for greater speeds. This innovation is not just limited to racing but is expected to influence recreational and transport vessels in the future.

Today, we see hydrofoils in action with hydrofoil kiteboards, which have become popular among thrill-seekers. This is due to their ability to harness wind power and achieve impressive acceleration and agility on the water. This same principle is being applied to larger sailing vessels, where performance and sustainability converge.

The further development of hydrofoil technology involves intensive research into materials and design optimizations that can handle the challenges of varied sea conditions.

Electric and solar-powered hydrofoils are on the horizon, poised to significantly impact our world by offering greener alternatives to traditional boats.

Notably, the trends in hydrofoiling indicate a shift towards more sustainable sailing, utilizing advancements in electric propulsion systems to complement the inherent energy efficiency of hydrofoil designs.

The goal is a fleet of sailboats that are not just faster but more eco-friendly, promising an exciting future where the joy of sailing is in harmony with the health of our oceans.

Related Articles

I've personally had thousands of questions about sailing and sailboats over the years. As I learn and experience sailing, and the community, I share the answers that work and make sense to me, here on Life of Sailing.

by this author

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Solo Challenge

Sailboats with foils: the evolution seen by Sirena, Soldini and Pedote

• Marco Nannini

In this article we tried to consult authoritative voices of sailing in explaining the evolution of sailboats with foils. Max Sirena of Luna Rossa, Giovanni Soldini of Maserati and Giancarlo Pedote of Prysmian Ocean Racing – IMOCA class.

Note: This article is a translation, we apologize in advance for any mistakes.

However, we also wanted to explain before moving on to the actual interviews why there are currently three “currents of thought” in the world of foils for sailboats. First, the purely flying monohulls like those of the America’s Cup, then flying multihulls, flying but capable of facing the oceans like Maserati, and then the partially flying monohulls like the IMOCA and the Mini 650.

As you can imagine, the three types are linked to the different rules, which in turn reflect different objectives and ways of facing the sea and navigation.

For the sake of completeness we should point out that there is a thriving world of other types of foilers. For example, inshore flying catamarans, legacy and evolution of the previous America’s Cup. Many dinghies are also emerging in addition to the first flying dinghy, the Moth. Foils have also entered the world of windsurfing and kytes.

The increasingly widespread use of foils for all types of boats prefigures one of the most drastically and rapidly innovative historical moments, comparable to the introduction in the 1800s of the modern forms of jib and mainsail: today, as then, the paradigms of navigation seem to be definitively changing.

An introducion on foiling sailboats

If we talk about sailboats with foils we must first of all specify what is meant, since every sailboat is naturally equipped with many “foils”. In fact, in its semantic definition the “foil” is a “profile” capable of generating a force when it crosses a fluid. For example, sails have a “profile” very similar to that of an airplane wing and are therefore foils. Being flexible they change concavity on each tack. But it is precisely their air-foils that allows a boat to go upwind.

Even the fin of a keel or a rudder, if we observe the section, has its own profile, this time symmetrical, unlike a sail which has an asymmetrical profile. The study of the forces generated by sails, keels, hulls and rudders is a very complex subject, and the optimisation of shapes in naval engineering is constantly evolving, as can be observed looking at the boats produced today compared to those of only ten years ago.

For example, the keel in contrasting leeway also manages to create a force, called “lift”, which “pulls” the boat to windward. This is because of the leeway the profile of the foil has an angle of incidence with respect to the water that is not equal to zero (even if we do not notice it and we think we are going perfectly straight). The water then hits the keel at a slight angle and this means that despite being symmetrical, the keel foil generates an upwind lift and allows us to go upwind better.

Based on the same principle, the rudder blade also generates an upwind lift when sailing upwind. The sails work as foils as long as they are hit by a “laminar” air flow that follows the sail. On the other hand, when the sail simply opposes the wind from behind we travel in a turbulent flow and we are not talking about foils.

Sailboats with foils: so what is meant?

Keel and rudder have a specific role in the ability to sail of a sailboat. Their “foil” function comes into play from a reach to when sailing upwind, avoiding excessive leeway. They avoid it primarily by simple lateral resistance but also generating lift to windward.

We have seen so far that the sails are nothing but the great wings of our floating airplane. They exploit the kinetic energy of the wind with the  difference that a boat does not have an engine to generate apparent wind. Sailing upwind, sails transform a large part of the wind pressure into heel. Only a small part is transformed into propulsive force that makes the boat advance thanks to their wing shape trimmed to reduce heel and increase speed.

Old sails, for example, lose their “airplane wing” shape. They resemble C shapes or worse they have a claw near the trailing edge. When this happens, the wind hitting produces a heeling force force and any propulsion force is greatly diminished. Keel and rudder, on the other hand, counteract leeway when sailing upwind upwind according to the principles we talked about before, i.e. lateral resistance and lift.

Heeling: hull shape, ballast and stacking

It becomes clear that a sailboat is subject to different forces, some of which are useful to go faster, others that are not useful to generate any forward movement, instead they only waste energy in generating heel and leeway. The contrast to leeway exerted by the keel and rudder also introduces friction that reduce the “useful” forward forces. The evolution of racing boats, in order to avoid heel, has been driven towards the search stability of form or shape of the hull, i.e. hull shapes that resist to being heeled. The result has been wider and flatter hulls, and if we leave the world of monohulls, obviously catamarans and trimarans.

In an attempt to maximise the righting force, when the keels were still fixed, ballasts were introduced. Ballasts are tanks placed inside the hull and in the most lateral position possible with respect to the centreline, filled by hand or with a pump with sea water. Their role is to act as a counterweight, exactly the same as the crew sitting on the gunwale. The disadvantage of the ballast is that while making the boat more powerful, it weighs it down and therefore increases the resistance to movement.

In the classes where it is admitted, such as Mini 650, Class40 and IMOCA, the movable weights on board are used to generate righting force. That is, any bag containing water, food, clothing and other materials, as well as sails, everything, is moved to windward with the same effect of having someone sit on the gunwale and without the disadvantage of having to carry any additional weight.

A more advanced solution was possible, but it took time before we saw the first canting keels.

The canting keels and the first sailboats with vertical foils (daggerboards)

If we talk about keels, at first lead was inserted into the construction of the keel which constituted the bottom of the hull. Then keels then became separate elements from the hull, built for example in cast iron with the shape of an airplane tail wing. To increase the righting force and allow to increase the amount of sail (and therefore of “useful” force), the keels lengthened and the weight was moved to the bottom.

The fin is an empty box or a full blade shaped with fiberglass, which supports a lead bulb where the weight is concentrated. The advantage of this solution is the lowering of the centre of gravity of the keel and the consequent increase in the force that right the boat.

The modern solution is that of allowing the keel to tilt, so that in cross and upwind it can be canted to windward. By doing so, the righting force of the bulb weight increases considerably. However, this poses a problem: at the foil section is more and more horizontal it loses its function to counteract leeway. For this reason, looking at old IMOCA or Mini 650s we saw the introduction of “daggerboards”. These were addtional “weightless” fins inserted like swords in the hull, either a single central one or more efficiently one on each side, slightly inclined, to take on the role of the blade of the keel that is lost once it is canted to windward in counteracting leeway.

So what foils are we talking about when we say sailboats with foils?

The term foil has become fashionable, should refer to many types of foils but has started to take on a specific meaning, and represents the latest evolution in hull design. It indicates a specific type of appendage, which does not exist in “traditional” boats, which can have one of the following functions (or generally a mix of the two): increase the straightening force and counteract gravity and friction in the water.

These two objectives are therefore obtained with special profiles, “foils”. These are suitably angled to create new forces in the water that are more efficient than simple weight displacement or traditional shapes. Sailboats with foils can counteract friction by lightening themselves with the vertical thrust of the foils. We put “wings” in the water to lift and fly the sailboats with foils and we will progressively avoid the friction of the water until the friction of the hull is eliminated. The friction of the foils remains, which is not zero, but is much less than that of the hull.

It may seem incredible to you but the first experiments in this direction date back to the twentieth century. These were motor boats that accelerated and exploited submerged wings to lift the hull from the water. Nothing strange, you will say, today there are many hydrofoils around that use this principle to navigate at high speeds. There is a very famous foil sailboat that introduced this type of V-shaped foil to lift out of the water. This is the Hydroptere, a flying V-foil trimaran that has set many speed records.

The evolution of foils on sailboats

From here on, we will talk about foils in the sense of appendages immersed in water to increase righting moment or counter the weight of the boat. That is, we will not talk about sails or other traditional appendages. We will try to understand the evolution of the latest generation foiling sailboats. These include the America’s Cup boats, flying multihulls, and the recent generation IMOCAs.

The first evolution, as mentioned, was to try to increase the straightening force. After tilting the keel, why not put a “wing” in the water, downwind, that would generate and upward force? This type of side “blade” foil was introduced on boats such as Sidney Hobart’s winning Wild Oats XI. One of the first ocean sailboats with a foil to get results in races. In this case the foil was a straight blade that came out laterally creating a straightening force.

The second evolution was to give the foil an L shape. Why introduce this fold? The horizontal part has the role of generating upward lifting force. The vertical part has the role of creating that “lift” we lose when tilting the keel. These sailboats with foils are said to have “whisker” appendages. These foils revolutionised the Solitaire du Figaro with the Figaro 3 although in fairness here the keel isn’t canting so the role of the foil is not quite as extensive as we’ll see for an IMOCA.

Flying sailboats with foils

After the Hydroptere which had V-shaped foils like hydrofoils, the America’s Cup catamarans were the first to sail completely raised from the water. To achieve this, the foils a were in the shape of an inverted T or L so that the vertical part remained to counteract the leeway. The horizontal part instead serves purely to lift the hull. To improve the balance of the multihull it was preferable to have two lifting points. In fact, there is a second foil on each T-shaped rudder.

In the world of monohulls, on the one hand, there are two worlds: on the one hand, the totally flying boats of the America’s Cup. On the other, the world ranging from the Mini 650s to the IMOCAs where you never sail completely raised from the water. The two configurations respond to different objectives. A boat designed for the America’s Cup is designed for sheltered and flat waters and they fly within a span of the water. The design solutions would never pass the safety and stability criteria for ocean classes.

In fact, America’s cup foil sailboats depend on the foils themselves for their ability to stay upright. That is, if a foil accidentally comes out of the water due to a wrong manoeuvre, the boat will lie down. This without the ability to straighten up on its own as happened to Luna Rossa. Such a boat would not be allowed in either the Mini 650 class or the IMOCA class. Classes that require positive righting force when the boat is heeled at 90 degrees.

Sailboats with foils: a dichotomy between the world of inshore and offshore?

So far we have dealt with two types of foiling sailboats: America’s Cup inshore boats and ocean foiling sailboats such as IMOCAs. However, there is a third hybrid type, represented by multihulls with ocean foils. A multihull relies entirely on its enormous stability of shape to stay “straight”. Making it fly was a temptation that was imagined even by Leonardo da Vinci. We have seen that a multihull relies entirely on its enormous stability of form to stay “straight” and that beyond a certain maximum heel angle it is unable to right itself.

From that point of view, an America’s cup monohull and a foiling Multihull are more similar than to an IMOCA. An IMOCA without one of its foils loses performance but can still sail. Alex Thomson proved it at the 2016 Vendée Globe by finishing second despite having irreparably damaged the starboard foil in the first half of the race. In the world of IMOCA, external foils have existed since the 2016-2017 edition won by Armel Le Cleach in front of Hugo Boss.

The 2020 edition will be the second for IMOCA with foils and the evolution of the foils themselves has been immense. Giancarlo Pedote reports speed differences between his boat and new IMOCAs that reach 4-5 knots. The foils have been modified to make the average speeds more consistent. The first foils in fact created a huge lift when the boat accelerated. But when it slowed down due to a wave, it decelerated very violently. The boats were very tiring for the skipper and all the developments were in the direction of making them more manageable.

Let’s pass the word to our experts to talk about sailboats with foils: Max Sirena, Giovanni Soldini and Giancarlo Pedote.

What do you think of the evolution of foila in both monohulls and multihulls?

Max sirena – monohullls, america’s cup.

Bio from Pirelli Prada website: “Born in 1971 in Rimini, Massimiliano“ Max ”Sirena is in his seventh participation in the America’s Cup. Of these he won the 33rd edition with BMW Oracle Racing in the role of head of the wing shaft. The 35th with Emirates Team New Zealand in the 2017 edition of Bermuda. Max was skipper of the Extreme 40 Luna Rossa and winner of the Extreme Sailing Series championship in 2011. “

“With the Luna Rossa team he participated in the 2000 challenges, winning the Louis Vuitton Cup. In 2003 and 2007 in the role of assistant bowman. He then became Skipper and Team Director of Luna Rossa in the campaign for the 34th America’s Cup, held in San Francisco in 2013. Today, still in the role of Skipper and Team Director, he is at the helm of the Luna Rossa Prada Pirelli team. Ready for the challenge for the 36th America’s Cup which will be held in Auckland in 2021. “

Max Sirena’s point of view on sailing boats with foils – America’s Cup

“I believe they are the present and the future of world sailing. It is part of a development and research process, which will lead more and more sailboats to use foils. Performance and speed at a certain level are the maximum expression of design that you can find today. Everyone wants to go faster and faster, there are ocean speed records to beat. Compared to boats of the past, today certainly a well done project that uses foils is definitely faster than a displacement boat.

I believe that the use of foils in the America’s Cup has spread this concept in various classes. From there it has greatly increased the technological development used by teams or solo sailors. Along with the foils there are automatic flight pilots, new sail profiles and so on. This has given the opportunity to new sailors and new designers to make their way into a very narrow and niche world. The foils should not be seen as a substitute for the traditional way of sailing. It is a new discipline that still uses the wind as a driving force. So it is always and in any case a sailboat, but with different technical and performance characteristics “.

Giovanni Soldini – Ocean multihulls

Bio from the Maserati site: “He was born in Milan on May 16, 1966 and began sailing as a child. He has 25 years of ocean racing behind him, including two solo circumnavigations. The Around Alone won in 1999 where he went into the history books for the rescue of Isabelle Autissier.

He took par in the 1995 BOC Challenge, where he finished second overall. Then the Québec- Saint Malo, winner in the monohull category. Six Ostars, two victories in the 50 ‘and 40’ class, three Transat Jacques Vabres, one victory in the 40 ‘class and more than 40 transoceanic crossings.

On board the Vor70 Maserati he set important records such as the Cadiz – San Salvador record (2012) and the New York-San Francisco, Gold Route 13,225 miles in 47 days 42 ‘and 29 “. His is also the new record of the Tea Route. 3300 miles in 21 days 19 hours 32 ‘established in 2015 on the San Francisco – Shanghai route. In 2016, after an intense three-year period on the Maserati VOR70, a new challenge with the Maserati Multi70 began for Giovanni Soldini and his team. A return to the multihulls on which he had raced as a crew with the 60 ‘Tim trimaran “.

Giovanni Soldini’s point of view on sailing boats with foils – Oceanic multihulls

“Everyone has to live within his time and whatever is considered modern at that time. I am fortunate to have experienced a great evolution, I did my first circumnavigation still using SSB radios and the radio amateur Pierluigi from Ravenna who called me once a week. Now that we have ADSL on board the trimaran, and boats too, they developed and took their different paths.

The modern IMOCAs seem like crazy boats to me, even the new, flying mini transats, Verdier has designed one for the Pogo that will be standard, with these T-foils they are impressive, it is a revolution. An account with a multihull, a navigator is more used to being an airplane, while on a monohull it is really crazy. “

“The advantages are that the boat is faster and the distances get shorter. There are disadvantages in light winds because with all these appendages you have in the water they slow you down. If there is not enough wind to make you fly, you are slowed. With 3 knots you take a Moth and a Laser and the Laser will turn around the Moth that can’t even sail. In long crossings we do for records the impact with the waves is reduced. It is less than traditional boats, as long as the wave doesn’t get too high and doesn’t make you fly.

There is a limit in which you become less aerial and more displacement. When the sea is very formed, multihulls are more disadvantaged in this case than mono hulls. It becomes almost dangerous for the multis slamming on the waves. A boat that flies over the water and goes so fast is a lot of adrenaline, then every boat is special for me”.

Giancarlo Pedote – IMOCA

Official biography: Giancarlo Pedote, 44, has lived for some time in Lorient, France, one of the capitals of ocean sailing. Here he moved to live his profession to the full. Its history begins with windsurfing and crosses different classes of ocean boats. Mini 650, Figaro, Class 40, Multi 50 (the parenthesis of the Moth) and the IMOCA 60.

Winner of the Transat Jacques Vabre in the Multi 50 class in 2015. 2 times Champion de France Promotion Course au Large en Solitaire. 2 times World Champion in the Mini 650 class. 2nd at the 2013 Mini transat, Sailor of the Year 2013 and 2015. Pedote will be the only Italian present at the Vendée Globe 2020, a race dedicated to IMOCAs.

Giancarlo Pedote’s point of view on sailboats with foils – IMOCA

“I felt privileged to experience the introduction of foils in displacement boats, I wonder if such an important revolution will have followed in sailing. That is, we left the principles of Archimedes to make a boat fly. So something very important from a historical point of view. I am not sure it can be repeated from a qualitative leap point of view. Technology will continue to develop many things. But, as airplanes have changed the transport when they were invented, foils will significantly change the way of navigating .

I believe that for me to experience this transition at 40 is a great privilege. Our IMOCA class monohulls in terms of sensations are very close to multihulls and I have done a year of multihulls. The boats are very violent, very physical, the positions inside are difficult to find. The impacts are important and clearly they have become very demanding from a technical point of view.

With foils all the loads on the mast increase, a certain number of load pins are needed because if you increase forces too much something breaks. You need to know how many tons are on your mast and how they are distributed. All this requires meticulous preparation without considering all the development that still exists on the foils. Just look at Prysmian Group is a first generation foil boat, now many boats have changed the foils.

The differences between the recent generations of IMOCA with foils

The results are remarkable: boats sail upwind with 18 knots of wind and go at a speed of 18 knots. The boats that have newer foils do 4-5 knots more than me. So there is still a lot to develop on this.

As far as I’m concerned, witnessing this change and having the awareness of it given by my maturity in my career is extraordinary. I await future evolutions with curiosity and interest. “

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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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Home » Blog » Sail » Hydrofoil boats for the rest of us

Hydrofoil boats for the rest of us

By Author Fiona McGlynn

Posted on Last updated: August 18, 2023

Glide Free Foils Laser on foils. Photo credit: sailboats.co.uk ,

Watching foiling boats fly around the America’s Cup race course, is enough to quicken any sailor’s pulse. But unless you’ve got a spare few million kicking around, most hydrofoil boats are still very much out of the average boater’s budget . There are however a few ways to experience the magic of foiling without racing towards bankruptcy.

HOW DOES HYDROFOILING WORK?

Much in the same way that air flows over and under aircraft wings to create lift, water flowing around a hydrofoil lifts a boat’s hull out of the water . Once the greater part of the boat’s surface area is out of the water, friction is greatly reduced and the boat can “fly” at faster speeds .

How fast? The 2021 America’s Cup AC75s are expected to reach top speeds of 40 to 50 knots!

Like sails, foils are not a matter of “set it and forget it”, instead the foil-attitude must be adjusted to keep the boat in flight . On the 2017 America’s Cup boats these adjustments were made by the skipper/helmsman but powered (via a hydraulic system) by crew grinding winches (or in New Zealand’s case, pedal bikes ).

Because we don’t all have Jimmy Spithill ‘s magic touch, developing highly sophisticated flight control systems is key to bringing foiling into mainstream boating. Candela, a new 25-foot production e-foiling powerboat (and 2019 Best of Boats award winner) offers such a solution with foils that change position 100 times per second! Still, at ~$240,000 it’s well beyond most boating budgets. 

Fortunately, smaller foilers (dinghies and boards) don’t require high tech flight control systems and are far less expensive . Here are a few options for (more) affordable foiling:

HYDROFOIL DINGHIES

Laser foiling kits.

Clip a foil onto your Laser and fly over the surface of the water. Two Australian based companies, Foilsz and Glide Free Foils , offer Laser foiling kits. The Glide Free kit doesn’t require any permanent fixtures, so you can easily remove it (for those days when you’re in a displacement mode mood). They say that speeds of 18-25 knots are possible with their kit, which sells for just under $4,530 AUD (~$3,00 USD). 

UFO foiling multihull

For a few bucks more you can buy a foiling catamaran. The UFO was launched in 2017 and can fly at 15-20 knots. With a price tag of $7,000, it may be the most economical multihull foiler on the market.

Take a foiling course

Some clubs and community sailing programs are adding foilers to their fleets. For example Nantucket Community Sailing offers a 3-hour semi-private class for $100 per person . Or if you’re looking for a more exotic locale, the Provela Foiling Centre in Spain offers a range of foiling classes from beginner to advanced. Their two-day “Try Fly – Foiling” class costs 200 euros and their fleet includes Foiling Moths, White Formula Whispers, WASPZs, and F101s.

HYDROFOIL KITEBOARDS

It’s not like kiteboards are sluggish to begin with, but hydrofoil boards take the sport to a whole new level, delivering speeds of 40 miles an hour ! By using a foil to lift their boards out of the water, foiling kiteboard enthusiasts get an exceptionally quiet and smooth ride – so much so, that   kiteboard riders in Silicon Valley have been spotted taking calls on their cell phones. Set up costs start at around $1,000. Take a foil boarding course and buy protective gear, this extreme water sport is not for the faint of heart.

HYDROFOIL WINDSURF BOARDS

Foiling is taking off in the windsurfing world with world champions like Robby Naish and Atoine Albeau leading the charge. It has been confirmed that windfoiling will be a class at the 2024 Olympics in Paris . Set up costs start around $2,500. 

With foiling technology trickling down into the mainstream, you can expect to see more and more high speed foiling boats and boards on the water .  Is foiling the future? Let us know what you think in the comments below.

Fiona McGlynn is an award-winning boating writer who created Waterborne as a place to learn about living aboard and traveling the world by sailboat. She has written for boating magazines including BoatUS, SAIL, Cruising World, and Good Old Boat. She’s also a contributing editor at Good Old Boat and BoatUS Magazine. In 2017, Fiona and her husband completed a 3-year, 13,000-mile voyage from Vancouver to Mexico to Australia on their 35-foot sailboat.

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Four small boat pvc-foil furlers.

The development of reliable headsail furling must rank high on any list of devices that have significantly changed the way boats are sailed in the past two decades. Hanked-on sails, while having certain advantages, are disappearing in favor of roller furling jibs and genoas. Furlers keep the crew off the bow and reduce time spent sail handling. And thanks to improved designs, the sight of a tattered furling genoa flogging itself to death also is disappearing. Jams, once the bane of furlers, are much less frequent.

Practical Sailor has tracked the evolution of headsail furling for many years. In 1988 we undertook a comprehensive evaluation of available models and followed that in the May 15 and June 15, 1995 issues with a follow-up evaluation backed by a reader survey, which showed marked improvement in performance, reliability and customer satisfaction. At that time, 77% of all survey respondents said they would buy the same furler again, led by Cruising Design Inc. (CDI) and Famet (an older system) at 100%, followed by Profurl, Schaefer, Harken and Furlex.

In the November 15, 1997 issue, we again updated the group, highlighting the new Hood SeaFurl 5 and redesigned Furlex.

The Small Boat Market Average boat size in the 1995 reader survey was 32′. The number was drawn down a bit by the 25′ average size of boats equipped with CDI Flexible Furlers. Indeed, CDI has made a living selling furlers to owners of smaller boats, especially so-called “trailer sailers.” And while the other major manufacturers, such as Profurl, Harken, Hood, Furlex and Schaefer, have long offered their standard furlers in small boat sizes, and even some simplified models such as Hood’s Line Drive, none tried seriously to compete with CDI’s PVC luff extrusion.

The advantages of the plastic luff are several. First, unlike rigid aluminum luff extrusions, which are shipped in lengths of about 6′, and must be connected with splices or link plates and fasteners, pliable plastic extrusions are one piece and require no assembly. More and more boat owners are buying furlers from mail-order houses and doing the installation themselves. Secondly, the PVC can take a fair amount of abuse and is not as easily dented as rigid aluminum extrusions, an important consideration for any owner when stepping and unstepping the mast. It is of particular concern to owners of trailerable sailboats who handle the mast a lot. Thirdly, cost is less, making furling more affordable for owners of small boats.

Plastic won’t corrode, of course, but is subject to ultraviolet attack. Nevertheless, the addition of UV inhibitors should give them adequate life spans.

Three years ago, CDI’s dominance seemed about to change when Harken announced its first Heli-Foil, which used a PVC luff extrusion with an inner polypropylene sleeve over a braided stainless steel core. There were problems with it, however, and they took a long time to solve. Undaunted, Harken persisted and the new Heli-Foil is now available.

Not to be outdone, Hood Yacht Systems introduced its economical Sea Flex and Schaefer developed its SnapFurl.

We obtained furler kit packages of each, roughly sized for boats up to 24′ with maximum headstay lengths of about 30′ and maximum turnbuckle pin size of about 3/8″. Exact specifications are given in the table on p. 14.

Considerations All four foils come tightly coiled with warnings not to start cutting the bindings willy-nilly. There is a lot of energy packed in these foils that could cause an injury if handled carelessly. Most tell you to make sure the air temperature is at least 70°F and to uncoil outdoors; if it’s colder than 70°F, warm the foil indoors. CDI urges installers to uncoil within 24 hours of receipt so that the foil doesn’t take too much of a set. Observe directions regarding which end of the coil to start cutting free first as there will be a feeder near one end.

While all are flexible, they should be stored flat in the off season (assuming you’ve unstepped the mast). Allowing them to droop deeply also can cause them to take a set. They can be removed and coiled again, but Harken cautions that repeated tight coiling can reduce the life of the foil.

Because PVC is temperature sensitive, the manufacturers warn against exposing the luff extrusion to high heat—around 130°F-140°F. Such temperatures might be found under a boat cover in hot climates.

Presumably to reduce costs, only one of the four offers a line guide attached to the drum; that’s Schaefer and it’s a $23 option. This makes proper placement of the first lead block critical so that the line doesn’t chafe on the cage as it exits the drum.

The luff tape sewn to the jib or genoa will be #5 for Harken, Hood and Schaefer, #6 for the CDI Flexible Furler 2.

Ease of furling is affected most by the bearing surfaces, but also by the ratio of the foil diameter to the drum diameter; after all, the difference in the two is what gives you a mechanical advantage. The higher the ratio, the more advantage. We measured all four and developed these approximate ratios: Harken 2.5, Schaefer 2.14, Hood 1.65, and CDI 1.45.

Installation for any system will be easiest with the mast down but because you won’t have to completely remove the headstay for shortening the wire it is possible to do with the mast stepped. Nevertheless, you will have to unfasten the forestay from the stem to slide on the luff extrusion and torque tube/furling drum. Take a halyard forward to a strong attachment on deck, such as a toerail, to hold the mast while you work.

All four systems are fairly simple, with few pieces. The average do-it-yourselfer should be able to install his or her own with basic tools. The one critical job is cutting the luff extrusion to the right length. All manuals give explicit instructions—measure twice, or three times, and cut once.

Halyard restrainers may be necessary with any furler (except CDI with its internal halyard) if the angle of the halyard to the upper swivel is less than about 5°. A restrainer is a simple fitting that is screwed to the mast and through which the halyard is led to increase the angle. This is to prevent “halyard wrap,” in which the length of exposed halyard between the mast and the swivel wraps around the headstay as the sail is furled. You don’t want this!

Compared to larger boat furlers, these—especially the CDI and Sea Flex—are simpler and lack such features as integral adjusters.

CDI Flexible Furler 2 Joe Dahman bought CDI in 1984. At that time, Dahman said CDI was building furlers “on the floor” with metal luff extrusions and plastic links, which had a tendency to break. His first idea was to switch the materials. In the course of investigating and testing plastics, he came upon the idea of making the luff a continuous length, thereby omitting the link plates that trouble nearly every furler. If made of the right material, this single-piece luff extrusion would be much less resistant to damage when raising and lowering the spar, and enable CDI to ship the extrusion coiled in a box. He sold his first Flexible Furler in 1987 and since has delivered more than 10,000. He holds a patent on the flexible luff for which Schaefer is licensed by CDI; Harken and Hood are not.

Price is $515 list, and discounts through Defender Industries (800/628-8225) to about $300.

Unlike most furlers, the CDI uses an internal halyard, which eliminates the halyard swivel at the masthead. This places the furler in compression, not tension, and so the bearing is under less load. The halyard runs up inside one of two opposing grooves in the luff extrusion, through the Halyard Top Fitting, then back down to the head of the sail. The luff is not tensioned by this halyard, however, but by a short length of 1/8″ line seized in two to three parts between the tack of the sail and the downhaul shackle on the spool flange.

The standard furler comes with a UHMW polyethylene bushing as the bearing surface, though an optional bearing race is offered for $70 list. But instead of lots of small bearings, the FF2 model has seven 1/2″ Torlon bearings in a small race. Dahman says that a few large bearings work better and are more reliable than lots of small bearings, which have a greater tendency to get hung up on dirt or other debris in the race. The bearing kit is available as a retrofit; you can do the job in about five minutes.

Dahman has refined the system over the years, adding a few parts here and there. In 1990 a thrust bearing was added and in 1994 he replaced the aluminum cup or cage with stainless steel. For 2000, he enlarged the center hole to accept 5/16″ turnbuckles, crimped a ferrule to the halyard to secure the core to the cover where the line has been decored, and uses a larger 1/4″ braided halyard. Because the 42″ x 40″ coil size of the FF2 requires some straightening of the luff, CDI now offers a 6′ large hoop that is slightly less expensive but costs $60 to ship air freight. It does not require straightening.

There is no stainless feeder, like the Schaefer and Harken, just a slot in the foil, same as the Hood Sea Flex.

The manual with photos and drawings is adequate, if a slight bit confusing to follow at a few points.

The 3/16″ furling line is small to handle; we’d upgrade to1/4″.

In answer to criticisms that plastic luffs twist more than an aluminum luff, Dahman counters that aluminum twists more than people realize, principally at the section links, and that some twist is beneficial in spilling air in gusts.

CDI makes eight sizes of the Flexible Furler, from the FF1 to FF8, which is for maximum headstay lengths of 47′, 5/16″ wire and 1/2″ pin size.

CDI offers a lifetime warranty to the original buyer.

Bottom Line: The least expensive of the four, the Flexible Furler is simple and has a good track record with PS readers. It would be our choice among non-ball bearing models.

Schaefer SnapFurl Schaefer Marine has been making headsail furlers longer than just about any other company, dating to the 1970s when it made simple upper and lower bearing swivels for use with wire luff headsails.

Schaefer entered the modern era with its 1000, 2000, 3000 line in the early 1990s. It has since refined those models and more recently added its SnapFurl small-boat furler. It discounts to about $365.

SnapFurl’s single-groove foil is made of round, extruded PVC in two parts that snap together and interlock, which probably helps it resist twisting. The opposing forces of this joint also help the PVC straighten itself; Schaefer’s Fred Cook nevertheless recommends laying the PVC out in the warm sun for a while before assembly. The foil coils in a 34-1/2″ box.

The torque tube and drum are also injection molded plastic, a “long-grain nylon composite with UV inhibitors.” Bearings are Torlon, with two races in both the head swivel and drum. The two-part cage is stainless steel as is the sail feeder. The fasteners are captive so they won’t fall out if you have to disassemble the feeder.

The six-page manual with drawings is adequate.

Cook said that his company’s intent was to design a furler that was price competitive with CDI but retained some of the features of its other furlers, such as Torlon ball bearings and the ability to fit over the existing turnbuckle. It was also advantageous to use the same foil material as their Tuff Luff racing foil. They also wanted to price the SnapFurl lower than the Harken 00 Heli-Foil. About half of all SnapFurls are sold in Europe—France, England and Germany—Cook said.

Bottom Line: Innovative snap-together foil; stainless cage, feeder and aluminum upper swivel, and ball bearings make this a premium system at a low price.

Harken 00 Heli-Foil The Heli-Foil uses a PVC foil but with a polypropylene interior for what it says is an improved bearing surface. The PVC is cored with braided stainless steel for greater torsional rigidity. Of the four examined, Harken’s looks like it will resist twisting the best. Also, Harken’s foil is the only one of the four that has double grooves; this enables you to hoist a new sail before completely dousing and removing the existing sail.

With racers in mind, the two-part drum also may be removed as well as the halyard swivel, though the latter is probably more trouble than most owners will want to endure (you must rig a temporary headstay and disconnect the turnbuckle).

Discount price is about $700.

The drum is made of plastic while the cage, torque tube and halyard swivel are black anodized aluminum. Double races of Torlon bearings are used in each bearing. A torque tube key locks the foil inside the torque tube. A special clevis pin is required for your turnbuckle, available from Harken when you order your furler. It is longer than your existing clevis pin and locks the lower bearing fork to the turnbuckle and stem fitting.

Like Schaefer, Harken manufactures a complete line of accessory hardware.

Harken’s manual is excellent, with clear step-by-step instructions and accompanying photographs—the best of the group.

Bottom Line: The most expensive of the four, the Harken 00 Heli-Foil is also the most sophisticated with its stainless braid-reinforced PVC foil and aluminum parts; it’s also more versatile, should removing the drum for racing be of interest. Ideal for a J/80 or F/24.

Hood Sea Flex Sea Flex’s one-piece PVC foil is flat, like the CDI Flexible Furler, but has only one slot as it does not employ an internal halyard. It is reinforced with a 1 x 19 stainless wire running its length. This is supposed to help keep the foil from twisting but probably won’t be as effective as Harken’s larger diameter reinforcement.

The torque tube and upper swivel bearing are injection molded parts. The upper bearing has two races of Torlon ball bearings. The lower bearing is simply the stainless steel fork (which attaches to the turnbuckle with a clevis pin) turning inside a Teflon-impregnated Delrin insert in molded grooves in the lower end of the torque tube. Obviously this isn’t going to be as friction-free as one with ball bearings. However, it turned fairly easy…until we assembled the cage.

Like Harken, Hood’s lower bearing fork fits over the turnbuckle so that the clevis pin locks both to the stem fitting. On CDI and Schaefer, the pin simply passes through the slot in the turnbuckle body, which could cause it to unthread if sturdy cotter pins are not used to prevent the studs from turning in the body.

The fork has a second set of holes in case one wants to raise the unit with link plates.

The torque tube is cast in two pieces with threaded brass inserts for the six fasteners. The top and bottom of the drum are also black plastic and snap into grooves in the torque tube. They are easily removable for racing. The cage looks just like those on the SeaFurl 5; it is stainless steel. Assembly is quick, intuitive and actually quite clever.

The cage is held stationary by two pins snapped into the fork and also fits into grooves in the top and bottom cage parts. Thus, the plastic top and bottom cage parts revolve around the stainless, creating what we felt was excessive friction—certainly the most of the four furlers examined. When we queried Hood Yacht Systems’ Mike Haber, he admitted it turns roughly at first, but said that as the system wears in during actual use, there will be no problems furling.

Like the CDI, there is no metal feeder, just a slot cut in the foil.

The 8-page manual has drawings and is adequate.

Bottom Line: Hood Yacht System’s aim was to price the Sea Furl close to the CDI FF2, and it has done that—$311 at discount. While cleverly conceived, friction is a concern.

Conclusion Between the two least expensive—Hood and CDI—the latter has a bushing bearing at the bottom, with optional ball bearings. Hood does not. In addition, CDI’s internal halyard reduces friction. While we like Hood’s clever design, the CDI is a bit less money and has a long track record of customer satisfaction. At least until more experience is gained with the Sea Flex, we’d go with CDI. Owners of the Sea Flex are invited to give us their comments.

Schaefer prices out not much above CDI and Hood. It has just about everything Harken does—ball bearings top and bottom, many stainless parts, and what appears to be a good two-part luff extrusion—at a much lower price. It rates a Best Buy, hands down.

The Harken Heli-Foil is top quality and its split drum and excellent double-groove foil makes it the clear choice for performance sailors.

Contacts- CDI, 100 Cummings Center, Suite 106F, Beverly, MA 01915-3056; 978/922-5936; www.sailcdi.com. Harken Yacht Equipment, 1251 E. Wisconsin Ave., Pewaukee, WI 53072; 262/691-3320; www.harken.com. Hood Yacht Systems, 7712 Cheri Ct., Tampa, FL 33634; 813/885-2182; www.pompanette.com. Schaefer Marine, 158 Duchaine Blvd., New Bedford, MA 02745-1293; 508/995-9511; www.schaefermarine.com

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Home » Homebuilt Hydrofoil for Sailboats test sailed – end to hiking out?

Homebuilt Hydrofoil for Sailboats test sailed – end to hiking out?

Launching our Homebuilt Foil stabilised dinghy – this article is to use our experiment as the basis for low cost foiling that anyone can use to build or modify a boat – it sailed nicely in 5 to 10 knots and I didn’t have to do any hiking.

This is not about outright speed (wrong hull type for a start). It is about stability without hiking out. On the other hand if it works on this boat … it will work on anything!

No worthwhile video I am afraid – little wind when the photo boat was available on Sunday. We will get some next weekend with luck.

This is part of a four article set

• Part 1 – Sailing Trials in 5 to 10 knots of the hydrofoil stabilised dinghy.
• Part 2 – Building a Hydrofoil Stabilised dinghy – and proposal for comparison using any hull. Up later today
• Part 3 – Video in more wind – Next weekend if there is wind!
• Part 4 – Three Homebuilt hydrofoiling Projects – democratising foiling! Up Next week

Myth busting Foiling Boats – you don’t need a factory and you don’t need carbon fibre.

Everyone knew this once – because the recent history of making foiling work was achieved with homemade foils using timber and fibreglass.

The great Myth about foiling boats is “that it is high tech and everything has to be carbon”. But all the significant development in the Moth Class was with wooden hydrofoils that were fibreglassed with only small amounts of carbon or stainless steel.

The specification itself is to provide a basis for cheap experimentation and comparisons of performance.

The Foiling Moths advanced so quickly because there was a specification and people messed around with the spec and shared information. Wood and glass make fast modifications to homebuilt hydrofoils easier (and cheaper)

Maybe even racing if anyone has a mind to. But also as the basis of comparison with boats in other areas.

What does it feel like – a homemade foil stabilised boat upwind

We had good luck for the first day of testing – 5 to 10 knots and a well sailed Oz Goose as a pace boat. Started to get a feeling of the speed potential.

This section is about that.

Second day when we had a chase boat with cameras – of course the wind died. Hopefully we will have video next weekend.

The lateral foil to leeward needs to be kept in the water in the lulls. In 5 to 10 knots this meant sitting a little to leeward.

Initially as gusts hit I would follow instinct and make the wrong move. Hiking out brings the foil would to near the surface, would ventilate (suck air from the surface) and then the boat heel and slow.

Well … it is obvious … sit to leeward in the lulls, when the gust comes let the foil do the work – don’t move out to windward.

No Hiking. But with the same sail they were hiking in the accompanying Oz Goose .

So what to do when a boat with a lateral foil heels?

Don’t move your butt! Ease the sail and point a fraction lower to get the boatspeed up. The lateral foil starts to rise because of more lift – fly it up again.

Then I could wind in the sheet again to increase the heeling force. It is a feeling like flying. Boat heels then get speed without increasing the heeling force. Wind drops, move your body a little to leeward. Sheet loads seem higher – greater stability than hiking?

It becomes quite mesmerising watching the foil a foot or two below the water surface.

As the foil produces lift there is a depression in the surface of the water above the foil – which turns into a series of waves that make up the foil wake stretching back. It it like being followed by a small Loch Ness Monster.

It does also show that the homemade hydrofoil is developing lift at low speed.

The photo is at a very low windspeed/boatspeed. These wavelets go quite a way back. On Saturday with more wind and boatspeed I thought the transom was digging in and making a commotion.

But, it was the combination of the hull’s sternwave and the foil’s wake making a noisy quarter wave on the leeward side

So this is the exciting thing – not pure speed but less physical effort

At the moment many foiling systems are more or less being retrofitted to conventional boats.

Many of those boats are very wide – like the IMOCA 60s or some of the supermaxis.

Interestingly it is more moderate beam boats that win most races. They are faster in light winds, faster upwind and can sail deeper angles downwind without losing speed. A bit easier to steer too.

The question is … if we gain stability from a lateral hydrofoil – what is the beam for?

Canoes are light, fast and easy to store and transport. But can be hard to hold upright. PERHAPS this is a good place to start.

Another aspect is that modest length boats for disabled sailors have limited stability (and speed) because the centre of gravity of the crew is so high.

I also think about what will happen when I can’t hike out so hard. That’s why I win Oz Goose races. But I can certainly feel it in my 60 year old bones. The day is not close, but it is coming.

The inspiration of the Quant 28 and 17

Normally a keelboat this size without a canting keel would need 5 to 7 people on the rail.

Same lateral foil but a more beautiful version by Hugh Welbourne for Quant Boats in Switzerland.

The lateral foil is the simplest possible lifting foil.

In terms of stability – see how the crew on the Quant 17 go from full trapezing and hiking to sitting inside the boat when the foils are deployed and to leeward as soon as the boat has any downwind component.

I’m interested in the stability component.

In homebuilt hydrofoil boats Ian Henehan’s modified Oz Goose saw him chuck the hiking wings and start sitting inboard too.

It was like this with a hiking rack before – no longer needed. Simplification and less effort.

Perhaps: an advantage of some rocker for foiling dinghies

We didn’t fit a rudder foil at this stage – even though we built the rudder extension.

The purpose of a rudder foil on all foilers is to hold the main foil at an optimum angle of attack. Usually the rudder foil is adjustable in some way to allow the adjustment of the angle of the main foil.

If the rudder foil is sent lower then the angle of attack of the main foil is increased.

But with the 8ft boat with the extreme rocker it was possible to move back to increase the angle of incidence of the main foil. The base angle is 2 degrees Angle of Attack relative to the static waterline of the boat.

In the gusts of around 10 knots, going upwind, it was possible to move forward or back to reduce or increase lift – speed changes from doing so were instant. So where you sit in/on a rockered boat is a critical tuning factor.

Less rocker might be OK, but some rocker is going to be important. Maybe concentrated in the back end of the boat. I’m not sure if the foil fitted IMOCAs do this with water ballast.

Overview of comparison sailing the hydrofoiled boat against the larger Oz Goose

This is not necessarily a question of speed, though it is nice to get.

Our 8ft boat is absolutely sub optimal as a foil stabilised boat.

• It is short, so potential hull speed is low – 8ft long. This limits foil lift (square of velocity).
• It has a lot of rocker (fore and aft hull curve)
• Crew weight is a very large part compared to the boat volume – it was meant to be a prototype kid’s boat but the curved cockpit was too hard to build. So we repurposed it.

Saturday it was sailing around in company with Job and Jazmine in a Goose who I compete against in that class. They are among the top sailors in the Oz Goose so I know the speeds they hit. And the new boat has an Oz Goose Rig but is only 8ft to the Oz Goose’s 12ft length.

In the lighter patches it was noticeably slower than the Goose, but it was still sailing properly (felt normal/good). It was a faster choice to retract the foil. Pushed out to windward the hydrofoil is above the water to reduce the wetted surface.

With a bit more wind and foil deployed it started to equal the goose upwind. This is not something the shorter boat should be able to do.

The biggest difference – no hiking. While Job and Jazmine were hiking in the Oz Goose I found it best to move to keep the foil in the water in the lulls – which meant I was sitting centrally or to leeward and not hiking in the gusts. It is low effort sailing.

Downwind differences – was the 8ft foiled boat able to stick with the 12ft Oz Goose?

Downwind the Goose should have walked away from the smaller boat. I’ve a lot of experience with the 8ft Oz Racer and a GPS and know the boat tops out at around 4.2knots or just about 5. It can go quite a bit faster (up to 8knots) but it takes a lot of wind and it drops back to the 4 to 5kn range as soon as the gust drops slightly. The Goose, however just loves to accelerate into the 6 7 or 8 knot range and on stronger wind days gets up in the 8 to 12 knot range. And beyond.

So the Goose should get away from the shorter boat.

It did … but not too dramatically. More comparative trials to come.

Now we hope there is more wind next Saturday when we have the photographer and a chase boat.

Foiling Week 2018 Pt 2 – Foiling Sail for the rest of us!

Our recent articles on homemade foiling and

2 thoughts on “homebuilt hydrofoil for sailboats test sailed – end to hiking out”.

We just post an abstract of your pages about foils in our web site. Thanks for your job. Best regards Danilus

Merci Daniel!

Can you provide a link here to the article on your website.

Also we hope to get more wind to show how the foil behaves. We had one day of moderate wind but no photo/video boat. But last three weekends have had very light wind – sub 5kn. A more active video when Poseidon grants our wish.

Best wishes Michael

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