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

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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.

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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.

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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.

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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.

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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.

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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.

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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.

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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: 32m2 (345ft2)
Headsail area: 16m2 (172ft2)
Gennaker area: 50m2 (538ft2)