SOLD FROM THE BEGINNING – Charles Bertrand


I was still a student when DSS went ‘live’ for the first time. Hugh Welbourn and Gordon Kay had just gone public and the idea immediately appealed to me as a very sensible way to use foils on monohulls. At that time DSS had already been tested but only on a handful of boats, mostly under 30ft. It took another few years before I got the chance to experience the foil for real on an Infiniti 36; truth is the acceleration and increasing stability with speed were pretty convincing – as was the reaction of other guests onboard. The owner of my latest project (Plume) wanted a yacht around 9m with moderate beam (3m) for transportation, maximum performance and low sailing weight. The canting keel was already part of the brief but I immediately saw the benefits of adding a DSS foil. The boat would be faster in many conditions and the foil would make this light-displacement boat more powerful and smoother to sail. I believe a DSS foil combines well with a canting keel, which brings the extra stabil- ity upwind and at lower speeds when the foil does not deliver of its best.


We compared two 9m concepts: the first had twin asymmetric daggerboards, the second featured the DSS foil plus a single central daggerboard. The benefit of this set-up is versatility: the foil can be deployed to generate vertical lift independently of the side force requirement.


Time available was limited, so I asked Hugh to use his VPP to compare the two versions. The polars from the VPP were convincing enough for the owner to choose DSS… the path of innovation. But it was important that innovation did not come with high risk; helpfully Hugh and Gordon gave us full access to their knowledge of how to make the DSS foil work best. Given the size of Plume we elected to stay with the single foil sliding from one side to the other through the bilge to keep a maximum of space available down below. The foil span is also smaller than the over- all beam to reduce the hassle coming in or out of a berth, but it is still enough to lift 50% of the displacement at speed. Since we had chosen to cant the keel using hydraulics we decided to use the same method to move the foil, installing a very compact hydraulic motor to drive the foil from one side to the other via a belt. Charles Bertrand studied yacht design and marine CFD in Southampton, going on to work as a yacht designer as well as taking over the lead role for board and hydrofoil design at kiteboarding company F-ONE


FOILS GOLD – Brett Bakewell-White


I think we must accept that while the yacht design and construction world is often touted as cutting edge, a maritime space race, or some iteration of F1 on the water, the reality is that much of the development is more to do with rulemakers and fashion,


Left: Charles Bertrand’s Plume splits out the resolution of lift and side force with a daggerboard plus DSS foil; class rules force Imoca 60s to address both functions with a pair of ‘wavy’ foils. 2005 and this 30m maxi (above) is one of the first DSS designs to be run in the Wolfson Unit tank


with image just as important as function. New technology is always interesting and exciting, and sometimes quite amusing in how it is marketed as the latest thing and how hi-tech the industry is and so on. The reality is most things have been done before in some way or another, but they haven’t been embraced by the mainstream either because the materials and construc- tion techniques of the time were not up to the job, or in many, maybe even most cases, because the ‘rules’ didn’t allow it. The current wondrous new technology of foiling multihulls is an excellent example of something that was developed and played around with in the 1950s and 1960s and yet now in the post-AC34 period it is the new modern idea that we all must have. A previous example of post-AC hysteria was the winged keel that became a must-have for every production yacht in the world in the mid-1980s. So when a ‘new’ idea comes along I


usually take a bit of time to consider the context, the marketing, some history, and then look to see whether it is something that applies to our work. In most cases the tech- nological ‘breakthrough’ has limited applica- tion and once the hype has died down there is a realisation that it isn’t really going to transform yachting for the great unwashed. I have always subscribed to the notion of appropriateness – yes, all things are possible, but are they appropriate to the project at hand? I also subscribe to the KISS principle – too often the added complication of a technology will diminish the enjoyment of sailing, rendering it inappropriate. So where does DSS fit within this? Is it the new nirvana? Should we be fitting boards to all of our yachts? Probably not. But there is a difference here.


The development of DSS has not come from a single high-level rule-driven campaign coated in glitter and hype. The concept has been developed by a couple of individuals who went looking for a solution to a perceived problem – an alternative to a different technology which they saw as an unhealthy development in sailing. You can almost claim that it is a tech-


nology travelling against the flow and one that is only now making its way up into the higher echelons of sailing – the current crop of Imocas taking the technology


onboard, although with the DSS concept hampered by the limitations of class rules. This interest from various campaigns and more established mainstream design- ers can only be good for the developing technology; we will see the DSS concept applied in different ways and in combina- tion with other technologies. Although Dynamic Stability Systems have already developed, with a number of yachts using the technology and showing that it works, there is still plenty of untapped potential to be investigated.


One of the current issues is that the tools and budgets available to predict the performance of the system are limited. We are currently working on a design that will be using DSS in conjunction with what we see as complementary technologies, and our biggest headache is figuring out what level of performance we will actually see. Conventional VPP analysis is giving some pointers but some of the figures seem so optimistic as to be unbelievable. While CFD in some ways supports these predic- tions, currently there is simply a lack of solid data to confirm our predictions, partly because our project is of a scale yet to be explored in the real world. The decisions regarding the size and aggressiveness of the foil and its position in the yacht are possibly the most difficult. How complex do you make the control, and when do you stop research and simply build something and go sailing? There are a lot of unexplored avenues that could lead to interesting developments in the future. There are of course structural and space considerations that will vary depending on the size and purpose of the yacht in question. The loads can potentially get quite large on a big yacht, but not unman- ageable. To date Hugh Welbourn has conceived and proved a number of options for deploying and controlling the DSS foils and I am sure that others will continue to develop alternative methods.


It would be foolish to expect DSS to solve all the world’s problems – the level of performance will be dependent on condi- tions and the design and style of yacht to which it is being applied. The new Imocas are an example of this, where there is a trade-off in one corner of the performance matrix for a bigger benefit in another area. Outside the racing arena there is also room for considering the use of this tech- nology for cruising and superyachts, where righting moment might be restricted by draft limitations and where a designer might be looking for sea-keeping benefits as much as speed alone.


DSS cannot be all things to all men, but it does offer an interesting addition to the options available to designers. And, thank- fully, rather than banning the idea through ignorance, most rulemakers appear to have embraced the concept and are offer- ing to rate yachts using DSS, even if with a fairly blunt adjustment until more is known about the performance profiles of yachts armed with the technology.


q SEAHORSE 45


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