Wing of desire

We look at the changes made to the BMW Oracle Racing tri and speak to Design Director, Mike Drummond

So finally BMW Oracle Racing’s solid wing sail has been revealed, but the sailing pics of the boat reveal substantial changes to the platform too. Significantly, considering the legal machinations going on over measurement - specifically whether a transom hung rudder is included in the measurement or not - the rudder and the daggerboard on the centre hull of the trimaran have gone, while the rudders in the floats appear to have been enlarged.

This rudders on floats only is something we haven’t seen on a racing tri since the days of Formula 40 when they tried this on Jean le Cam’s Biscuits Cantreau tri. The loss of the daggerboard in the main hul – the board fitted with a trim tab - is more significant as the loss of this is likely to have a considerable impact on the tri's pointing ability. However clearly the team believe that they can get enough lift to weather from the curved daggerboards in their floats – the photos show a small vertical portion of the bottom of each board still sticking out when the boards are in their ‘raised position’, although this doesn't seem to be the 'hook' that featured on the end of the boards on the ORMA 60s.

We hope this move to boards only in the floats doesn’t result in the same unfortunate outcome as that of Herve Cleris' Multi50 Prince de Bretagne, which also only had boards (albeit straight up and down ones) in her floats.

So in short, the BMW Oracle Racing tri is heading towards becoming more of a D35-style quasi cat-tri. When it is light and the main hull is in the water, in theory she should have less wetted area than Alinghi’s cat (assuming the cat is also not flying her weather hull).

In addition to this the pictures show that the aft beams has been under the scrutiny of the ‘aero’ team. With the advent of the wing rig, gone is the main sheet track in favour of a single point main sheet (ie no traveller) and there is also a ‘soft’ fairing on the back of the aft beam. The trampoline between the beams has also all but disappeared – another step to reduce windage, although one imagines that for James Spithill this now makes the passage between his helm positions on the rear beam a little more death-defying. A soft fairing for some reason hasn’t been added to the rear of the forward beam, presumably because it would be in the way of the lines running athwartships between the floats and the main hull.

But the big news is obviously the solid wing rig, coaxed out of the America’s team design closet possibly a little prematurely following their recent dismasting.
Long term readers of thedailysail will be familiar with solid wing sails following our look at Steve Clark’s Cogito, the state of the art C-Class cat. This the former Vanguard Sailboats CEO built to challenge for the Little America’s Cup in 1996, winning it off Lindsay Cunningham’s Yellow Pages team. Clark only lost to Fred Eaton’s Canadian team two years ago. Clark is now believed to be beavering away in his shed in north Rhode Island, building a replacement for his 13 year old Cogito...

C-Class cats (as well as A-Classes) vary significantly from the competition BMW Oracle Racing is entering since they are limited to 300sqft maximum sail area - both upwind and downwind. Thus they are limited to using their solid wing rigs downwind (where they are undercanvassed by today’s standards), whereas the BMW Oracle Racing tri can fly headsails - as was the case with Stars & Stripes wingsail cat in 1988.

BMW Oracle Racing’s Design Team Director, New Zealander Mike Drummond, has masterminded the solid wing rig project and is both a big C-Class and an A-Class officionado too. “It has been an interest for a long time,” he says. “It is just a thrill to be given the opportunity. Larry [Ellison] has backed us to the hilt to try and improve the performance of the boat and taking the risk of the unknowns...”

Drummond confirms that they will be using genniker downwind and when conditions are light we can expect to see them flying genoas if they think they are underpowered. One gets the impression that at this stage it remains a slight unknown whether they think this will be necessary or not.

Due to their rig’s ability to fly headsails, another significant difference of the BMW Oracle Racing rig to Cogito’s is that is doesn’t have to be as efficient. Hence it only has two vertical elements, compared to the Clark C-Cat’s three.

“What they [the Cogito team] call the number two element, on the trailing edge of the main element, like a trim tab on a keel - we haven’t done that for a few reasons, the main one being that we will sail downwind with gennikers. The C-Class, because they sail downwind with the same sail area they go upwind with, their rig is optimised more for the downwind because they are lacking power, whereas we just put up a genniker in front of it to get the extra power. That second element increases the potential lift co-efficient by quite a bit, but we have not gone for that option.”

So the BMW wing rig is not quite the ultimate lift machine, built like a Stradivarius as Cogito’s wing is. However Cogito’s wing does not have to be 190ft tall...

While both Alinghi 5 and the BMW Oracle Racing tri will be capable of a fair lick of ultimate speed, what will be most impressive is what they can achieve in low wind strengths and the wing rig will certainly be superior to an equivalent-sized soft sail equivalent when it is light. But how robust is their new spar? “That is to be determined, but experience in the small boats I think we can manage this in 20 knots,” says Drummond. “If it is blowing 20 knots tomorrow, I guarantee we’ll chicken out! But I think we’ll learn to handle it pretty quickly and I don’t think there is any fundamental reason why we can’t sail in that much wind.” That will certainly be worth watching!

Due to the massive scale difference of the BMW Oracle wing sail compared to Cogito’s, its make up is quite different. Construction issues of something this size are likely to have also pushed the design team towards a simpler two-element wing, but they also have divided the trailing elements into seven independent sections.

“We built the trailing edge in sections partly for handling reasons and partly because we wanted to be able to control the twist a bit better,” says Drummond. “So in reference to the Cogito wing, there is only one control arm about two thirds of the way up and a few hinges. So because of the scale we have gone for more control arms. It is a bit of a trade off of weight - you have more arms, but then the spar of your second element can be lighter, so some of it is for practical reasons.”

Thus there is potentially a lot of string coming out of the bottom of the rig – however on the Cogito rig this is simplified with for example one control line pulling on several points of the rig to different degrees... The inside of a C-Cat rig has been described as being like the inside of a piano! According to Drummond they haven’t reached the simplification stage just yet.

“We have seven control arms, so seven pairs of lines. Potentially we can operate them all of them independently. How much we simplify it to one control - that will come out of the sailing. I am certainly expecting that we can simplify it to quite a degree. Obviously having them independently controlled, there will be some days with different twist or sheer or even wave conditions, where we will want that extra control. It is not going to be very complex to sail with, I don’t think.”

That, one would imagine, would rely on a significant re-jigging of the crew roles on board. However Drummond says this isn’t the case. “It doesn’t change that much in that the control lines are relabelled, if you like. Previously you used main sheet tension to control the twist as well as the camber, whereas now you have two separate controls for that – and the traveller is the traveller. So even though it is quite a different concept, what propels the boat is still just pressure forces on the sail.”

We figured for example that it would take at least one person to keep an eye on the twist in the sail given that there are seven elements - and twist can also be induced in the forward element, although to nothing like the degree it can in the Cogito rig.

“No, it is the same as a sail where you have to make compromises between how much camber and how much twist you have with regard to not just what the breeze is like, but how hard the boat is to steer in waves and the acceleration requirements and so on. So you will be globally trimming, just like a normal soft sail,” states Drummond, who is adamant that they will even let trimmers on board who don’t need PhDs!

While we have already mentioned the change in traveller arrangement, Drummond confirms that they have moved the mast step forward - presumably a fairly significant operation for the boatbuilders - but other than that they haven’t had to change the platform to accommodation their dramatic new spar.

In terms of area, Drummond couldn’t tell us off the top of his head, how the area of the wing compares with the upwind configuration of their previous soft sail rig. It is certainly very much smaller. ‘Two thirds the size?’ we propose to him and he reckons it is somewhere about there.

As to the performance gains over a soft sail, Drummound reckons it will be pretty much globally more efficient and thus faster, although he hedges his bets. “I think there will be a few points of sail and a few wind strengths where there will be either no difference or a slight advantage to the soft sail, but over an average range of conditions we’re not expecting that.”

Interestingly he points out that it would be possible to make a softsail to be as efficient as a solid wing, only that it would have to be a sail designed to a very very specific wing strength and angle. “I think that is the advantage and disadvantage of soft sails. The advantage is that they go through a huge range of conditions, and their disadvantage is that they are not as good as they could be in any conditions.”



Those involved in the design of the BMW Oracle Racing wingsail are: Joseph Ozanne (Research Leader), Dimitri Despierres (Wing Engineering Leader), Ian Burns (Design Coordinator), Tim Smyth (Wing Construction Manager), Michel Marie (Technical Director), Mike Drummond (Design Director), Scott Ferguson (Wing Designer), Herve Devaux (Wing Structural Leader), Thiha Win (Control System Leader), Thomas Gaveriaux (Platform and Interface Design), Steven Robert (Wing Composite Designer) and Andrew Gaynor (Wing Modelling).

However a name not appearing on this list is that of C-Class veteran Dave Hubbard, who is the man who back in the 1960s was attributed as begin the first to use a slotted wingsail on a C-Class catamaran and who’s designed subsequently won the Little America’s Cup on four occasions.

“Dave Hubbard - he’s been involved with us for about a year advising and doing some design work and just providing us with his experience and observations and insights,” says Drummond. “It has been great. He has got more experience of these types of rigs than anyone else. We’ve also had quite a team of guys doing the aerodynamic design and the detail design. It has been great having Dave for an overview. It is not new what we have done here, but we have applied modern methods and we have put in a few little innovations of our own and taken it to a higher level on the technical side. In aircraft terms this concept has been around since the 1920s or so - it is not a new concept at all. We have just taken it to a higher level.”

Construction-wise we haven’t learned a lot from Drummond, who had to race off to go yachting when we spoke to him, however like the Cogito wing, it does appear the individual elements are covered in a heat shrunk mylar film. “It is just a thin film so there will be some distortion around the ribs. But it will be acceptable. We had to make it light,” he says.

As to how they will put the wing to bed at night - they seem to be taking a slightly cavalier approach at present. The last two nights it hasn’t been taken down. “It stayed up all night dancing,” as Hubbard puts it.

We look forward to seeing the wing being used in anger and we wonder if it something that might ever see wider acceptance in yachting, rather than just fascinating but highly esoteric areas of the multihull world.

More photos on the following pages...

Further reading on C-Class cats/solid wing sails:

Steve Clark describes Cogito's rig - here
Christian Fevrier's Little America's Cup photo gallery - part one and two.
Video of the C-Class cats in action at the Little America's Cup in 2004.
Steve Clark demonstration on video how Cogito's wing works