DSS (Dynamic Stability Systems), could be how more of us start ‘foiling’. It’s currently the best way to use foils for speed gain in conventional monohulls. The lateral wing is deployed to leeward, generating lift which increases righting moment while partially lifting the yacht. As the speed goes up, so does the stability, meanwhile drag is dropping as there is less hull in the water. It’s a perpetual speed/fun increase and can feel like a fast multihull at times.

DSS is something most people will doubt until they try it, but as more experience the technology, it’s now appearing less experimental and more like a very effective way to increase speed while achieving a smoother ride.

Stability from speed, not weight

Three years ago I wrote a feature on DSS for this magazine following a quick blast on the 27ft prototype. That sail was enough to convince me of its potential but I left wanting to feel it all scaled up.

That opportunity arose last year, when I took a job working on the Infiniti 100S design, while overseeing construction of the second Infiniti 36. Fresh from 20,000 nm on a canting keel IMOCA 60, it was the start of new adventures in achieving stability and this took a bit of adjustment. No more excessive beam and massive rigs, DSS means a narrower hull and smaller, manageable sail-plans combined with very light displacements. Sailing the yacht is also different and speed takes a very high priority since this is ‘supplying’ your extra power, but most people seem to get the hang of it after a few hours.

These days, there are more DSS foils out there, and several other new-builds on the way, so it’s time to look at these and how the technology is progressing. English sailor Gordon Kay and Naval Architect Hugh Welbourn created and patented DSS, and aside from Wild Oats, Hugh is responsible for designing all recent DSS launchings.

Quantyachts

At the smaller, but by no means ‘slow’ end of the DSS scale, are Quantyachts. Michael Aeppli of Switzerland approached Hugh Welbourn several years ago with the challenge of creating a lake yacht with DSS that could enter production. To test the concept they launched the Quant 28 in 2011. A narrow, skiff-on-steroids with wings and a single DSS board, she won almost every race entered, including the famous Bol d’Or against a fleet of over 500 yachts.

The Swiss lakes are notorious for light airs, and sailors counter this with huge rigs and inventive ways of keeping upright when the breeze kicks in. Michael describes why he wanted to try foils, “With DSS you get ‘two yachts in one,’ the first yacht for light airs benefits from the foil indirectly. Thanks to the stability insurance from the foil you sail a very light and slender yacht with a lot of sail area. Boat two provides multihull-feelings in more breeze. There is a direct benefit provided by the foil to give the yacht a real afterburner as soon as you can open sails a bit.”

There is some dramatic footage on YouTube, showing the yacht reaching in the teens over glassy water, the hull raised up with the transom free of the surface, clearly showing the foil’s effectiveness.

Following this success, four orders were placed for the Quant 30, an evolution of the 28. Michael explains, “The main task for the Q30 was giving passionate sailors the performance of the Q28 and the effortlessness of ‘normal sports yachts of the European type’. Easy handling on and off the water.”

Key developments in the Q30 are the use of twin foils, which are curved and retract forward into the yacht, giving the following benefits:

Both foils can be used at once, providing a very stable platform downwind, trainer wheels if you like.They never have to be moved when loaded: the foil for the opposite tack can be deployed before the yacht flops over.The foil shape and structure can be optimised, as it’s only ever out one way. The sliding mechanism can also be simplified for this reason: On the Q30, lines are used as on a large daggerboard, instead of rollers.At the dock, or in light airs, the boards are retracted to be almost flush with the hull side.

There is a small weight penalty but so far everyone is satisfied with the twin board arrangement. The Q30 is also fitted with a furling jib on a self-tacker, retractable rudder, keel and wings that fold up to be level with the boom when docked, reducing beam to 2m. This is an all-carbon yacht, and could be popular in Australia, perhaps with a slightly smaller rig to match the breezier conditions. Retail price in Europe is around $200,000 AUD ex. works, with a rig from Applied Composites in Melbourne and Ronstan deck gear. www.quantyachts.com

Infiniti Yachts

Infiniti markets top-quality DSS equipped fast cruising and racing yachts. Their designs combine high performance and technology, sleek styling and lightweight interiors. Two Infiniti 36’s have been constructed by Danish Yachts, and although conceived as a day-sailor, both have competed in offshore races in the Mediterranean and racked up thousands of miles. They’re sophisticated pre-preg carbon creations, with carbon masts, rigging, foils, and even a lifting propeller system. I’ve sailed a lot on the second yacht, which features a gear/rack foil drive (think rack/pinion steering system on a car) instead of rollers, operated by buttons at the helm. The foil moves from one side to the other in 6 seconds, driven by an electric motor.

Without sounding too biased, performance in the light is spectacular, where her low drag and light displacement (2400kg) make her very responsive. In medium airs, the foil might be extended when going upwind to dampen pitching motions, but it doesn’t give a big speed gain.

As you crack off, and your speed rises to 8 knots, you start to feel it pushing the yacht upright. At 10 knots yacht speed, she’s sitting level and as you go faster, it keeps getting better. At 12-14 knots, you look behind and see the transom starting to lift from the water. The foil can support up to 50{7ab277620c5331e8b7880e6f86cbb80254c5854d4a7043b2f5807dffb54e9218} of displacement, so as you accelerate, the drag from the hull decreases and the speed rises easily, as on a multihull. What I’m impressed by is the trim when the foil kicks in, the bow rises slightly making it easier to steer in waves and there is no pitching or sharp changes in trim.

Like most people, I had some reservations about the system even after following the build and understanding its peculiarities. It wasn’t until we were on sea-trial in a choppy Mistral that I really ‘got it’. Running deep in 20 knots of wind for a few hundred miles, the yacht would just accelerate down a wave and keep going faster and faster while remaining very stable. I didn’t expect the foil to be much use at these angles, but it was seriously lifting the yacht which made for great sensations at the helm and a lot of fun, speeds steadily in the mid-teens.

Seeing the foil perform so well at higher speeds reassured me the Infiniti 100S, which we’ve been working on over the last year, will perform impressively. It’s a very light and relatively narrow 100 footer with a minimalist interior, designed to be comfortable cruising at +20 knots. The most challenging and interesting part is the quest to keep everything light and simple while providing enough luxury for six guests and four crew to live onboard. It’s the classic compromise designers are faced with, made all the more interesting by DSS, where the rewards for staying light seriously multiply.