Simon McGoldrick discovers a successor to the canting keel, and test sails the prototype in Spain.

Dynamic Stability Systems, or DSS, is the acronym on everyone’s lips at the moment. The system uses a curved foil (think horizontal centreboard) that runs athwartships and provides lift, keeping the boat more upright and reducing motion. It is deployed to leeward, and through tacks or gybes is slid from one side to the other. Simplicity is the key here, and it offers huge increases in righting moment without the complications of a canting keel or water ballast. Speed, comfort and easy handling: these are big gains from such a basic installation that impacts little on a boat’s interior. At the heart of DSS development is UK-based designer Hugh Welbourn, engineer Will Brooks and professional sailor Gordon Kay. This is not just a recent idea – they’ve been working on the concept for the last decade and with a number of prototypes now validating their predictions, have patented the technology. DSS is also venturing into the Superyacht arena by way of Infiniti Yachts, who debuted at the Monaco Yacht show with a range of yachts sporting the system. In addition, it has been approved by IRC, IMOCA (International Monohull Open Classes Association) and insurers Pantaenius. The scene is set for a huge revolution in yacht design.

How it works

The most significant benefit of DSS is stability. The foil produces an upwards force at a point well to leeward of the hull, helping to keep the boat more upright. It’s just like having a small outrigger, however the size of this force varies with speed (it is ‘dynamic’). The faster you go, the more upwards lift and therefore stability you get. It doesn’t take a genius to realise this has huge potential. As the boat accelerates, it becomes more level, the sails can be sheeted in and you can sail at a tighter angle. The challenge then comes in maintaining that speed, which means sailing in a slightly different way. The rewards from getting it right, however, make this
very worthwhile.

The second major advantage is motion reduction. Heave (up and down), roll and pitch are all dampened, making for
a smoother ride. Less motion results in a more stable flow over the sails and appendages, increasing their efficiency. The end result is that fewer of the crew will get seasick while reaching their destination in a much shorter time, a true win for those with a sensitive belly.

Out on the water

Canting keels have been the ultimate way to go fast since the early 90’s, yet the DSS promises another level of performance. Speeds up to 10 knots faster than a conventional design sound impressive, even optimistic. Can it deliver? I decided to find out, and flew to Sotogrande in Southern Spain to sail the 27ft prototype. This is a complete scale model of an earlier 100ft design, so is quite low and narrow compared to your typical sports boat. It also looks rather cool and menacing with that foil sticking out just above the waterline.

The boat was built in 2007 from a machined block of polystyrene and was designed from the outset to have DSS. It’s been on test here for several years and we had no trouble finding volunteers for a cool and blustery Sunday morning session. Firstly, you must remember this is quite a narrow, tender boat. Yet DSS allows it to plane at high speed, even close reaching where a conventional design would be on its side going slow. Once the foil has really kicked in it feels more like a multihull, moving rapidly and just gliding over the water. Incredibly fast, upright, and great fun: it’s easy to lose perspective of the wind angle as she is reacting so differently to a normal yacht. By the end of the session, I realised sailing on anything without a foil would
now be pretty boring!

However, the speed doesn’t come for free. The mainsheet must be worked during the transition from normal boat to foiler and the helmsman has to stay on the ball, keeping a careful eye on speed and wind angle.

Once up and going, things are quite steady and only small adjustments are required. If you are moving really fast, the foil starts lifting the hull out of the water, increasing the chance of rudder ventilation (not really a concern in twin rudder examples). But when sailed well, there is huge speed potential and offshore you could really eat up the miles.

Upwind the foil provides some assistance, but you still heel over. Speed is relatively low and therefore only a small amount of lift is produced. However, it continues to reduce motion, typically leading to a 5-10% increase in VMG.

On the DSS 27, moving the foil was as simple as pulling on the control line as we tacked or gybed. As size goes up, it is controlled by rollers, and in very large designs there’s a separate foil on each side operated by hydraulics. The foil’s angle of attack is fixed, and I was impressed with how well the boat trimmed through the speed range, with just the right amount of bow-up attitude.

Although the 27’s foil is oversized, on other examples it can be retracted to fit within the boat's maximum beam for easy berthing.

Racing with DSS: how will it rate?

Canting keels and water ballast never really took off in handicap racing: the added complexity, cost and rating burden relegated them to the Open and Volvo classes. Will DSS enjoy a different fate?

I spoke with Hugh Welbourn, who said, “We’ve been totally open with RORC (Royal Ocean Racing Club, who control IRC) and also ORC (the new version of IMS) with regards to what we're doing. With IRC, I supply them with information and we’ll jointly arrive at a suitable rating cost. We've had provisional numbers run which show that some of the time it will be tough, other times easy to win races. However, as we slowly move the general boat population into quicker boats, this will be less of an issue.”

At the other end of the spectrum, in the IMOCA 60 and Mini 6.50 classes, the use of DSS isn’t penalised and could produce radically different designs. Canting keels dominate this arena and have driven design towards wide, powerful hull shapes teamed with massive sailplans. The critical point here is the stability test – the keel is swung all the way to leeward and the boat must not heel past a certain angle. Designers increase form stability by pushing beam to the max and carrying this well aft, so the keel can be canted further before reaching the limit. The end result is a very high righting moment.

After racing in the Mini Transat, I’m a big fan of fat-transomed, powerful hull shapes. They surf easily, are forgiving under pilot, and the grip from the twin rudders is incredible. I’d choose a Mini over a more conventional design in almost every condition, except going upwind. This is where beam becomes the enemy – pointing is abysmal and the motion is stiff.

An Open 60 or Mini designed with DSS, however, doesn’t have to follow this ‘maximum beam’ path. Since heel caused by the foil to leeward is insignificant, the stability test is not a problem.This means beam can be reduced, and with it wetted surface area and weight. Upwind the narrower hull form will enjoy lower resistance in a seaway, and point higher. In deep running conditions and light airs, it should suffer less from that ‘stickiness’ so common to Open-class designs. When reaching, the foil comes into its own, providing the type of righting moment that would see you steaming past the best cant keelers.

Solo sailors use their autopilot a lot. Some rarely touch the helm. The success of DSS in these classes will depend on how well the pilot can keep up. In a seaway, speed varies and so does stability in this case. The pilot must adapt well to maximise the potential of the system.

Where can you buy one?

DSS are not boat builders, but they license designers and yards to use their technology, and work with these parties to produce a yacht that makes optimal use of the foil. In Australia, the 25ft sports boat Brace Brace Brace was the first DSS design to hit the water. Even shortly after its launch it was thrashing boats twice its size on Moreton Bay, and won the annual Bay to Bay race against a 170 strong fleet. Owner Paul Murphy commented, “The boat has unbelievable raw speed. The DSS 25 is very stable, very quick, and seriously good fun.”

In New Zealand, the aptly named Thompson 30 Drinks Trolley was fitted with DSS. It transformed this normally average racer/cruiser into a +20 knot speed machine. In the UK construction continues on the JK DSS 50 cruiser/racer, which should hit the water early in 2011. A Swiss company also have their pre-production 28ft racer about to launch in the UK. Over on the continent, a Danish group are developing a 50ft racer/cruiser, the first of which will launch in the final quarter of 2011.

For larger custom projects, Monaco-based Infiniti Yachts are targeting the Super Yacht market with a range of ultra fast DSS equipped yachts. They’re aiming to emulate the kind of style, pace and sex-appeal owners are used to enjoying in their Maserati or Aston Martin coupes. This recipe could be spot on – these boats require only a minimalist interior, and glamour on the outside is all about showing less these days. This makes a very light displacement possible and the idea of scooting past even the fastest of Wallys, thanks to DSS, could be enough to seal the deal for many clients. The first Infiniti will be launching in Monaco during the European summer.

Although retrofits are still possible, the designers prefer the new-build approach (or rebuild where a new hull is fitted to an existing deck) where DSS is an integral part of the project. The faster a boat can accelerate, the sooner it can utilise the stability from the foil. Minimising weight and drag becomes a very high priority in the design. The system also places certain demands on the boat’s structure that are best dealt with from the beginning.

So far it seems whoever sails the DSS walks away gobsmacked, with questions such as “where/when/how can I get my mitts on one of these?” This is a user-friendly device that has the potential to make sailing more fun, without breaking the bank. Gordon Kay summed it up well by saying, “Prospective owners can be reassured DSS is no gimmick and will not turn their boats into hard-to-control speed machines that can only be mastered by professional crew. Quite the opposite. DSS will provide a previously unknown level of control, and the handling and stable platform more typical of a larger yacht.”

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