Simon McGoldrick explains how DSS works.
The adoption of foils in the 34th America’s Cup transformed the event. It’s hard to imagine anything more captivating than high-speed 72 footers racing at close quarters while literally ‘flying’. So how can you make your own sailing more exhilarating? Even going half that speed would satisfy most, but unless you’re agile enough for a Moth, or have the space or money for a multihull, what options are left?
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 boat. 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 boat 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.
At the smaller, but by no means ‘slow’ end of the DSS scale, are Quantboats. Michael Aeppli of Switzerland approached Hugh Welbourn several years ago with the challenge of creating a lake boat 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 boats.
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 boats in one,’ the first boat for light airs benefits from the foil indirectly. Thanks to the stability insurance from the foil you sail a very light and slender boat 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 boat a real afterburner as soon as you can open sails a bit.”
There is some dramatic footage on YouTube:
http://www.youtube.com/watch?v=s9ilCx8B0A0, showing the boat 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 boats 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 boat, 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 boat 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 boat, 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.quantboats.com.
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 boat, 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 boat upright. At 10 knots boat 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% 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 boat 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 boat 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. Visit www.infinitiyachts.com or www.danishyachts.com.
Following the 2012 Sydney-Hobart, the Wild Oats team began searching for ways to stop the bow of their 98ft maxi burying in heavy downwind conditions. Numerous options were investigated, but they chose to install a ‘short’ DSS foil to achieve the bow-up trim required.
It would be deployed when needed off the breeze, even when travelling at high-speed.
Already fitted with a canting keel, they were not seeking to increase stability as this would place too much load on the structure and rig.
Wild Oats’ foil is moved using a gear/rack system as trialled on the second Infiniti 36, driven by a hydraulic motor. Clever support bearings allow them to slide the foil in/out when it suits, without having to slow down to reduce load on the board.
Although it’s early days and the system has yet to get a proper work-out and calibration, John Hildebrand has stated, “We’re sort of saying 10 per cent more sustainable speeds, from 18 knots upwards boat speed. That may be 20 per cent more depending on wind speed.”
Interestingly, DSS has always been marketed as a stand-alone system, to be used in place of a canting keel or water ballast. But I’m not alone in being very curious about a combination, and would love to see Wild Oats with a longer foil and a reduction in bulb weight. The potential for the foil to be effective over the entire polar range improves with speed: so a boat that already travels around at 10+ knots all the time will see great returns.
Creating a DSS Mini presents a conundrum – you are bound by the three metre maximum beam limit. What this means is that with the foil extended, the sum of the boat plus extended foil must be three metres or less. Hugh Welbourn’s solution, a 1.8m wide hull with the DSS foil and water ballast. It looks rather narrow compared to the rest of the fleet and this does little for the skipper’s ‘accommodation’ space.
But the Mini Transat story is filled with victories that resulted from radical innovation, not least the 2011 race being won by Magnum, a scow designed and skippered by David Raison. This boat was hardly an ‘all-rounder’, but its reaching prowess was so great that no one could catch it after the doldrums.
The race course has also recently changed, with the finish now in the Caribbean (instead of Brazil) which means a deep-downwind course after the Canaries.
In these conditions, and in the light, the DSS mini will be particularly fast thanks to its low wetted surface area and displacement.
The boat was constructed by Dominique Pedron at Isotop composites (who have incidentally made the majority of DSS foils). Hugh recently sailed her and commented, “It achieves its VPP targets easily enough even at this early stage, and is the lightest boat out there.” It will be proving itself on the French mini circuit in 2014, but since Dominique is too busy to take on the 2015 Transat, the boat is still up for grabs and a charter/sale is possible. Any takers? Contact firstname.lastname@example.org
But how does it rate?
The golden question for anyone who doesn’t have a chance at line honours is rating; how much is the foil penalised? Curiously, at the smaller end of the scale IRC punishes light weight, and even for the Infiniti 36 without the foil, the rating is a little tough. Yet move up in size and look at the Welbourn 53 Hi-Fi, which incidentally is structurally ‘ready’ for a foil, and the rating increase is very small.
The Infiniti 100S shows a similar trend, but things should become clearer as more boats hit the water.