On a Wing and a Prayer
Brothers Greg and Patrick Johnston have been pioneering and perfecting the wing sail for 30 years, admitting that their hobby (“obsession”) developed into their livelihood.
They say their Semi Rigid Wing (SRW) system is suited to almost any sized yacht, from small craft to superyachts. The simple and robust design means it can withstand the rigors of ocean sailing and racing.
In the early years, the market just wasn’t receptive to their concept. But then three things changed: “First, the 33rd America’s Cup came along and Oracle beat Alinghi convincingly,” explains Greg. “That put wing sails on the agenda. Then, the cost of exotic materials like carbon fibre has reduced by an order of magnitude over the years, and the cost of computing power has also dropped.”
The duo’s introductory production rig is fitted to the world’s first one design sports boat featuring a wing sail, the K8, which is already attracting worldwide attention, winning Yachts and Yachting Magazine (UK) 2016 Sportsboat of the Year.
Now, at the production ready stage, Greg and Patrick share their innovation and insight with Sails.
Why is your wing sail design unique?
[Greg] Our wing sail is novel as it uses mast rotation to force shape into battens in the wing membranes. So once put into shape the mast and battens form a semi rigid aerofoil frame that is covered by the wing membranes. This allows the shape of the wing to be changed to increase thickness and camber and for it to be set up on either tack. The mast becomes an integral part of the wing so mast drag is eliminated. This system is very light and very simple. It can be hoisted and reefed like a normal sail and it about the same weight.
How did the concept come to light – what inspired the first discussions and designs and when was that?
[Greg ] Patrick became interested in the hydrodynamics associated with the winged keel on Australia II in 1983. Consequently he started reading about hydro and aerodynamics. One of the texts that had really big influence on him was “Aero-hydrodynamics of Sailing” by Czesław Marchaj, which was published in 1979.
A topic in that book that gets quite a bit of attention in the effect that both the sharp leading edge of the jib and the mast of the mainsail have on sails. Patrick started thinking of ways to eliminate the mast drag from a mainsail and at the same time provide a better aerodynamic wing section.
What are your backgrounds?
[Greg] Patrick and I have had boats together most of our lives, the first when I was six and Patrick was seven, from sailing Mirrors and Flying Ants, to 16-foot and 18-foot Skiffs, to an 18-foot Hobie cat.
In my late teens and early 20s I got interested in Ocean Racing and while I was studying electronics engineering I also developed a range of Gore Tex offshore wet weather gear under the name of Nautical Systems. The Nautical Systems wet weather gear pioneered the use of Gore Tex fabric for sailing applications. At about the same time Patrick came to me with the wing sail concept and jointly we developed that through to a working prototype on an 18-foot Skiff.
I have worked in a variety of fields from mining and mineral processing, to telecommunications, to software development. I have an engineering degree and a Masters of Business Administration.
[Patrick] From a very young age I had a passion for sailing and building things so I pursued a career in boatbuilding. I had exposure to the early Australian AC 12-metre campaigns and when I first saw the A2 wing keel my life changed. I wanted to know how and why it worked. I started reading as my understanding of aero/ hydrodynamics grew so the SRW was born. I worked as a shipwright in 1987 for Taskforce 87 AC defence for Australia, while at the same time with my brother Greg building an 18ft skiff equipped with the first version of our wing sail. I have done a multitude of jobs in many different industries, went to university to study Environment, then taught construction of aluminium ships and ended up being in charge of a flight deck on an offshore oil rig.
My real passion is building high performance yachts. While making money doing such things, Greg and I were putting whatever we could into building and testing the SRW concept
What were the main challenges you had to overcome in its evolution?
[Greg] Initially our biggest concern was that the air pressure would cause the wing membranes to be sucked together, which would make the idea unworkable. Our first prototype was a 1-metre high rig made using balsa wood battens and spinnaker cloth on a wooden mast. We couldn’t afford wind tunnel testing so we had to improvise. We knew from our calculations that to get anything like the right sort of flows on a 1-metre model we needed about 60-70km/h of wind.
So we pressed Patrick’s Holden ute into action. We rigged the model up above the cab so that I could ride in the back and observe and adjust the sheet angle and it worked just fine. At about 70 km/h and 10 degree angle of attack the loads became a bit high for the materials used and it pretty much destroyed itself. A great success! Unfortunately it was before gopros! Another issue was dealing with twist in a 3-dimensional structure. Masts are inherently resistant to twisting. Wings (and sails) need to twist to account for wind shear and also to provide depowering and gust response. Twisting a pair of battens around a mast results in the wing section becoming thicker, which is exactly the opposite of what you want.
So we had to find a means of allowing twist to occur and yet either maintaining or reducing the section thickness. The result of this is a unique control system. We can now actually make the top section of the wing flat so that it feathers in gusts, or thicken it up if you require more power in light airs.
Staying a rotating mast on a narrow platform and getting adequate rig tensions was another challenge. We have now developed a rotating spreader system that allows us to carry normal rig tensions on a rotating mast.
Getting the mast shape right was also something that required some effort. The mast forms the leading edge of the aerofoil. It also rotates to create the aerofoil frame. It has to work on both port and starboard tacks. There is a relationship between the mast shape and size the effect that rotation has on thickness and camber. There is also a relationship between the mast rotation and the spreader rotation design. It took quite a bit of computer modelling to determine the right combination.
This also fed into batten design. We reviewed different mast shapes in combination with different batten characteristics, and modelled these at different rotation angles and other rig settings. The result is that we now have a good understanding of the mast shape and size requirements and limitations. This gives us parameter limits to work within for practical designs. This influences the structural engineering requirements. So all in all there is quite a lot of experience that goes into the design of any rig.
Eliminating weight is always a challenge for rig designers. Our goal has been to get our wing sail down to conventional sail weights. This has required the elimination of unnecessary parts and minimising the weight of the remaining parts. At the end of the day reducing the part count has multiple benefits. It reduces the complexity which in turn increases the reliability and reduces the cost.
All this has to be considered in the context of ensuring that the product is usable by normal sailors and can be manufactured easily. We are now at the point where we believe our designs are capable of being deployed in production boats.
What kept you motivated over these 30 odd years?
[Greg] Moments of shear brilliance in performance! Times when the set-up was just right for the conditions and the performance was just too good to ignore. Over the years of sailing with the wing had enough performance highlights to keep us motivated. When these happened, it surprised us how easily the performance came.
Learning how we did it was the turning point, once we were able to replicate performance over a range of conditions we made the commitment to build for production. For many years it was really a hobby for us. We had explored the market in the late 80s and really found that it was not receptive, but we just could not let it go.
The 33rd America’s Cup was the catalyst for dusting off old prototypes and for exploring the aerodynamics in a lot more depth. Venturing into CFD to explore the performance of the section shapes we were achieving was a breakthrough. I was surprised at just how good the numbers from the modelling were. The modelling also helped us refine our setups far more quickly that we could by prototyping.
What were some of the “moments of brilliance” and what did they indicate to you would make the project worthwhile/commercial?
[Greg] One poignant example was when we had re-assembled the prototype on our old boat, Shapeshifter, after quite a lot of computer modelling to optimise the setup. On the first sail we were sailing upwind in 15 knots of breeze. A strong gust, in excess of 20 knots came through. Rather than sheeting out to depower we just wound the boat up through 10 to 15 degrees to windward. It didn’t slow at all, if anything it went faster and way higher. And all of this was with very light helm and very easy control. Our 23 foot boat felt like a 40 footer going to windward.
Why do you believe in this system – how would it advance sailing, both racing and cruising?
[Greg] From a racing perspective, the wing brings into play new tactical options. You hear the AC sailors talking of modes – low and fast or high and slow. The SRW’s wide range of performance actually means that there are quite big differences between these modes. So you have a lot more flexibility in terms of race tactics.
From another perspective, foiling is the rage at the moment but I think this is ultimately going to push conventional sail technology to the limit. Foiling upwind results in very low apparent wind angles. The aerodynamic stability of a wing is really much better suited this type of sailing. Furthermore, a wing sail can enhance both upwind and downwind performance of modern non foiling designs. A more stable aerodynamic package will open up design options for yacht designers. Ultimately there is an opportunity to optimise the whole yacht/wing package. A more stable aerodynamic package will ultimately allow the size of control surfaces, like rudders to be reduced.
We are just at the beginning of a new technology curve and I think our wing sail has a part to play in pushing the performance envelope.
The application to cruising boats has the great benefits due to ease of obtaining high performance and the robust stable nature of the SRW. The SRW is much more forgiving than a conventional sail. It is much easier to sail a course with far less trimming and that translates to increased comfort and easier sailing. The inherent stability of the SRW means that it does not flog or flap. This means that the sails last longer. Tacks are quiet and far less dramatic. You basically sail the boat through the breeze, simply swapping the asymmetry from one tack to the other on the way through. When in “neutral” (when there is no induced shape in the wing) it just feathers, with still no flapping or flogging. All in all, this makes for a more pleasant, safer sail. Hoisting and reefing are much like on a conventional sail and the wing easily drops into lazy jacks.
Who else is onboard – do you have supporters, funding, people who believe in it too?
We are self-funded, which has limited the rate of progress, however, interest in the project is growing. We can always do with more support, so we are open to discussions with interested parties.
We have had great support recently. Elvstrom sails have worked with us to develop light wing membranes. NKE Marine Electronics are working with us to develop an instrumentation package suited to the SRW.
Our rigging partner Upffront Performance Masts and Rigging have developed a textile rigging package for the K8 Sportsboat and we will be working with them to provide rigging for other designs as well. C-Tech in New Zealand are working with us to put the SRW into production. We have had great support from Ropeye, who have supplied all of the soft rigging attachments for the K8. We have also had a pretty good deal from Harken who have supplied all of the deck for the K8.
And, of course, there is the team behind the K8: G Yacht Design Naval Architects designed the K8 around the SRW, Katabatic Sailing in Valencia have been working with us to promote the K8 and the SRW. There are other ‘believers’ and we will be making further announcements about other products soon.
When will we see it in mass production?
[Greg] The design is production ready now. We will be producing rigs for the K8 in the first half of this year. We are also looking to expand the range and have completed designs for an extruded aluminium “cruise” version. There are a couple of other things in the pipeline as well but it is too early to announce anything.