Leading British yacht designer Hugh Welbourn first contemplated the fitting of foils that create lift on the leeward side of a yacht when he sailed around the world doublehanded with the first Whitbread Round the World Race in 1973-4. Today his innovation has been realised through the company Dynamic Stability System (DSS) and its much developed foil systems, the latest iteration of which is now fitted to the DSS-equipped Baltic Yachts 142 Canova – the first foil-assisted superyacht.

Welbourn and his DSS business partner, another British round the world sailor Gordon Kay, first met 20 years ago when Kay was looking for someone to optimise the famous Whitbread maxi, the Baltic 80 Martela. This culminated in a class win in the 2001 Sydney to Hobart Race. Recognising they were kindred spirits, Kay commissioned Welbourn to design the 93ft Bols maxi, one of the fastest monohulls in the world at the time.

For many years prior to this, Welbourn has been refining his early foil designs and validating his concepts through tank testing for what would become DSS. When it was presented to him Kay immediately appreciated the simplicity and brilliance of Welbourn’s ground-breaking concept and so the Dynamic Stability Systems company was born.
Early full-sized DSS boats were tested during the mid to late 2000s. The foil system has since been both retrofitted to some of the world’s most significant yachts, such as the multiple Rolex Sydney Hobart winner Wild Oats XI and the American maxi Rambler 88. However, there are now many yachts to which DSS was central to the design from the outset. These include the Infiniti range including the 36 and 46 and the Swiss Quant range, initially the Quant 28 and 30, culminating in the extraordinary fully-flying Quant 23, the much-praised European Boat of the Year in 2015.

Among the French classes, Alex Thomson raced his DSS IMOCA 60 Hugo Boss to second place in the last Vendée Globe and DSS-style foils are now wide-spread across the fleet of round the world race boats, which in this next cycle will not only be used for the solo round the world race but also fully crewed in The Ocean Race (formerly the Volvo Ocean Race) in 2021-22.

As Kay puts it: “For some perspective, when we started sailing foiling monohulls with DSS, the America’s Cup was still being contested in 24 tonne monohulls and the Volvo Ocean Race in boats slower than our first Infiniti 36 daysailer.”

Today DSS has been tried on yachts of most sizes and types, but the association with Baltic Yachts and the launch of Canova marks the start of a new chapter of DSS-equipped superyachts, says Kay: “We always believed that DSS would fundamentally impact different areas of the industry, but superyachts benefit from the stability and comfort DSS brings, perhaps more than any other genre. On smaller boats draft and bulb weight can be increased to add stability. On superyachts increasing draft proportionally creates logistical issues such as not being able to enter harbours. But with DSS stability can be increased as it is required by deploying the foil. Superyachts are always looking for more stability, it is a simple question of physics.”

Achievements of DSS-equipped yachts:
European Yacht of the Year 2015 – Quant 23 – world’s first fully flying keelboat

25ft Brace Brace Brace including the Bay to Bay Race in Queensland, Australia and several similar results in Hong Kong.
Quant 28 won some big races in Switzerland – (awaiting details)

Quant 30 class established in Switzerland/Austria – (awaiting details)

Quant 23 class established – first class of fully flying keel boats

SEAir Mini – fully flying Open 6.50 Mini ocean racer, fitted with DSS

Fully flying 35 footer, launching next year for the Swiss lakes

Infiniti 36 – two ground breaking gentleman’s day sailors – third Palermo-Montecarlo 2012

Infiniti 46 – 1st in class Rolex Middle Sea Race 2016, 1st in class Rolex Middle Sea Race 2017, 1st in class RORC Transatlantic Race 2017, 1st in class Newport to Bermuda Race 2018, 2nd in division TransPac 2019 (1st boat under 50ft)

Wild Oats XI with DSS – two line honours wins 2013 & 2014

Hugo Boss – second Vendee Globe 2016

How does it work?
Stability is one of the principle drivers of the performance of any yacht as it allows greater sail to be carried in increased wind strength, which results, to varying degrees, in increased performance and speed. However, the traditional devices used to increase stability all have detrimental side-effects.
-Increasing draft limits access to shallow ports and anchorages on larger yachts and many superyachts have to fit lifting keels.
-Increasing bulb weight, increases drag and raises the boat’s overall weight requiring more power to drive it in the form of increased sail area causing more cost and complexity.
– Canting a keel to windward is effective but adds complexity in the keel attachment, the necessary hydraulics and requires an additional foil or foils to prevent leeway.
– Increasing waterline beam increases the stability generated by the hull but increases drag, detrimental to light wind performance.
– Pumping water ballast up to a tank inside the weather rail is effective but again adds weight and takes up valuable interior space in a cruising yacht.

Aside from increasing hull form stability, all of the above solutions effectively add downward force to the weather side.
DSS – the genius solution – instead provides upwards force on the leeward side, effectively at the opposite end of the stability ‘see-saw’. The foil is deployed to leeward where it provides lift while passing through the water, exactly as an aeroplane wing does while passing through air.

Of the above solutions, all aside from the canting keel and water ballast, provide a fixed amount of righting moment, regardless of conditions or the requirement for added stability. The ‘D’ in ‘DSS’ refers to ‘dynamic’ which means that the faster the boat goes, the more upward force the DSS foil automatically provides to counter heeling moment.

One of the “S” in DSS might also refer to ‘simplicity’, because unlike the foils used on America’s Cup multihulls and monohulls, DSS foils are inherently designed to work well across a broad range of conditions and points of sail without the need for additional trimming (be it manual or computer-controlled). With DSS you simply deploy the foil and forget about it until you tack or gybe.

As mentioned, DSS works by using the forward motion of the yacht combined with a retractable foil to increase stability. The DSS foil, set to leeward of the yacht and submersed in the water, creates lift. This lift is produced ‘dynamically’ – so when a gust hits, the yacht heels and accelerates and this acceleration through the water causes the DSS foil to produce extra lift to leeward, countering the heeling force. This extra stability, kicking in automatically whenever needed, translates into a marked increase in performance.

But the DSS has several additional benefits. The added dynamic stability it produces means that a boat can be designed with a narrower hull shape. In light conditions the DSS foil is simply retracted leaving a slippery low drag hull shape. In high performance yachts it can result in a reduction in keel bulb size and drag.

The lift the DSS foil produces, not only creates stability countering the yacht’s rotational heeling moment, but in strong conditions it also serves to lift the entire vessel, thereby reducing drag, again increasing performance.

For superyachts, DSS offers two additional and perhaps less obvious benefits. The added stability reduces heel, the foil encouraging the yacht to sail upright. The foil also reduces fore and aft pitching. Both of these motion-reducing features significantly improve on-board comfort – very welcome features for all yachts, particularly superyachts where comfort is a priority.

Why now?
While Baltic Yachts was insightful enough to consider DSS ten years ago for application within a project at the time, there is a deep conservatism within the superyacht industry to adopt new technology particularly one so ground-breaking, despite the array of evident benefits DSS holds.

Today DSS is becoming ever more widely accepted. It has proved itself in so many spheres of yachting and has now come of age adequately for superyacht owners to consider it for their new builds or, where suitable, for retrofitting. The Canova project has provided the perfect fusion of ambition, vision, experience.

How will it change the industry
Following the 20 years DSS has already spent in evolution and development, along with the incontrovertible proof of its concept, Canova is the first application of DSS on a superyacht. Aided by her DSS foil package, Canova is proving herself to be faster and more comfortable than any comparable sailing yacht.

If motor yachts often get chosen in preference to large sailing yachts because of the added comfort they offer, the reduced heel and pitching DSS offers to sailing yachts may help correct this imbalance. The additional argument that the fixed speeds capable of displacement motor yachts helps make the most of the guests’ time on board during passage is also much reduced by the increased speeds achievable under sail with a DSS-equipped yacht. The sailing yacht option also has a hugely reduced carbon footprint – a welcome feature being demanded increasingly by ecology-conscious owners today.

The brief for Canova
While DSS has worked with Farr Yacht Design on previous Infiniti projects, DSS had very little to do with the initial brief for Canova. However, as soon as DSS became involved, due diligence was carried out by all sides and with the ambitions of the owner understood, an immediate rapport was built. The DSS foil rapidly became an integral part of the design, Farr and Baltic embracing and exploiting the benefits that DSS brought to the yacht. Specifically, this meant that due to the added righting moment and resultant loads, the engineering of the rig and sailing systems was revised to take full advantage of the benefits of DSS.

DSS – early decision
It should be noted that if DSS is integral to the design of a yacht from the outset then the knock-on benefits are significant. A DSS yacht is typically lighter overall, in turn offering increased efficiency and lower cost construction, simply through less materials being used. This is not an idle boast, but a process that has been proved repeatedly and one that is more relevant the larger the yacht. Optimisation of all systems and the sail plan around the DSS foil is the hallmark of the Infiniti design process and one the company is developing with Baltic Yachts for some ground-breaking future projects.

Gordon Kay, CEO, Infiniti Yachts


Hugh Welbourn, Naval Architect