Father of Canaan

Designer Steve Killing talks us through the development of Fred Eaton's C-Class Canaan

Yesterday demonstrated that once again the top dog in the rarified world of C-Class catamarans are the present defenders from Canada, Fred Eaton and Magnus Clarke aboard their immaculate Canaan.

Eaton’s C-Class cats now number four and this excludes Patient Lady VI following its sale to Antoine Koch’s French team. He had two boats built prior to the 2007 Little America’s Cup - the unsuccessful foiler Off yer Rocker, and their winning machine, Alpha. In this cycle they built Orion, being raced by Glenn Ashby and James Spithill in Newport this week, following it up with the ultimate masterpiece Eaton and Clarke are sailing this week - Canaan.

The man behind the design of all their C-Class catamarans, although this is far from a one man effort with crew Magnus Clarke in particular involved with the design of the wings, is Canadian, Steve Killing.

While the focus for the last Little America’s Cups has been primarily on the exotic solid wingsails the boats use, this time around there has been much more development with hulls.

The hulls of all the Canadian boats have had even less volume that Steve Clark’s benchmark Cogito. Over the four C-Class cats that they have built they have experimented in particular with volume distribution and the degree of rocker.

“Orion is a very good boat in flat water – it has tiny bows and a lot less rocker in the hull,” says Steve Killing, by way of comparison with their latest Canaan. “It goes through waves well and doesn’t pitch very much, but we found the drag of going through the wave is greater than going up and over, which is why it is not our number one boat. In flat water it is quite potential.”

Compared to Alpha, the two new boats Orion and Canaan have more volume in their bows and more rocker.

“In our analysis, the two things you are always trying to get rid of are straight frictional drag and wave-making drag,” explains Killing. “It seems more and more that because these hulls are so skinny, the wave-making drag is not a huge part of the equation, it still comes in but it doesn’t take over like it does on a monohull. So getting rid of surface area is critical and the way to do that is to have slightly more rounded sections and a little more rocker in the boat.

“The secondary benefit seems to be when you are about to fly a hull it is much easier to get the windward hull off the water - it floats off very nicely as opposed to the flat rocker boats which are stuck on for a little while. So the take off and landing are very soft. Fred [Eaton] is very happy with the way it behaves in waves and he is feeling very good about the boat.”

According to Killing the boats can fly a hull in as little as 3-4 knots, although this requires the crew being down to leeward and having the helm in the middle of the trampoline. As he puts it: “If you are not flying a hull at any wind speed you are not sailing right.”

Another development between the 2007 generation Alpha and the new Canaan is that the latter is unique in the C-Class fleet for having her rudders mounted beneath the transom, like larger catamarans.

“Getting the rudder underneath is more efficient so you have got the nice end plate from the hull giving you a significant amount more lift from the top of the rudder,” says Killing. “The other rudders that are out the back – at the surface the lift has to be zero because it is turning to air there, so we have cavitation plates there to stop the air from sucking down on Alpha. But still there is quite a bit of disturbed water coming out of the back of the boat hitting the rudder. So [on Canaan] we moved them under the hull and it has cleaned up the flow a lot and it has allowed us to put on an even smaller rudder. I think in the camp we have eight sets of rudders for the different boats, some with elevators on them and some without and every time we make a smaller rudder, Fred still likes it more, so we have some pretty tiny ones now!”

Obviously the main issue with having rudders under the hull on what are effectively large, highly refined beach cats, is that practical issue of launching. Understanding this Killing came up with a system that would make this as easy as possible. The boat is launched, the rudder stock in each case inserted from underneath, and then there is a pin and sliding wedge arrangement to ensure that the rudder is fully pulled up into the hull and locked in place. Killing is pleased with the result: “It is faster than installing our external rudders. So I would do that again for sure.”

They have left any extreme developments with the daggerboards to others. Orion and Canaan have higher aspect boards than Alpha and they are curved, but this is not for any cunning ORMA 60-style reasons of trying to induce more lift into them, but that they remain street-legal under C-Class rules, staying within the permitted 14ft beam.

Steve Clark’s new Aethon platform takes a more extreme approach to the boards and has them hinged at the exit through the bottom of the hull, allowing them to be canted laterally.

Killing says that they tried curved boards on Patient Lady VI and explains why they haven’t gone down this route: “The challenge is that at high speed in the C-Class as you go faster and faster you want to pull the board out, because if you don’t then you start making negative leeway which is creating more drag on your hull. So you’d like the leeway of the leeward hull to be zero. So the goal is that you are pulling area off the board as you are going faster and faster, but on a curved board that means you are reducing lift more and more which is the time that you want it. So we didn’t like having the lift tied in so closely with the amount of board you have down.”

Obviously the part of the boat we are keenest to hear about is the magnificent solid wing sail, that under C-Class rules must measure (measuring is no mean feat in itself) no more than 300sqft upwind or down. This time around the wings all have the same general concept, unlike when we attended the Little America’s Cup in nearby Bristol in 2004, when Team Ronstan  a more 'solid' wing and Invictus Challenge had her 'split flap' wing. This time around all the wings comprise three vertical ‘elements’, the middle one being a flap attached to the back of the front element, featuring a ‘slot’ between the middle and rear elements.

They all have essentially the same controls: to adjust the wing’s overall angle of attack; camber between the three elements and the twist in the front and rear elements. The hard/complex parts from the wing designer’s standpoint are how to ensure that the control line settings automatically tack and control of the slot size. The slot is integral to the solid wing sail design as it allows flow to Venturi from the high pressure side of the wing through to leeward encouraging flow to re-attach on the low pressure side of the wing. The designer's headache is how to keep the slot size constant when the camber of the sail is adjusted – typically the slot should be closed at zero camber then open out as camber is induced, but to open out no more once the camber goes beyond a certain point.

Steve Clark demonstrates on video how all this worked on the recently deceased Cogito wing here.

The wing on Canaan has all these controls, including the main twist controller affecting the front main element, plus a separate twist controller for the rear element. “Steve Clark refers to it as 'wash out' in the wing,” says Killing of the latter. “I’m not sure myself if it is washout or twist, but it is doing a similar thing - it permits the depth of the sail to get smaller as you go up and the upper leech to open out more."

In terms of how the Canadian wings have evolved - two identical wings built for the Canadian teams 2007 generation boats were identical. However a significant difference with them compared to the Cogito wing was that they were only half as thick. “We did a lot of work in foil shapes that were appropriate for that wing and we felt that with the narrow size we got more maximum lift and we got a little less drag upwind, but in downwind it proved out on the water that we had a little more max lift too," says Killing. "The other benefit of having a narrow wing is that you can build it lighter - there is just less material and light weight in these things is pretty critical.”

But the principle evolution on from the Cogito and Alpha wings and on to Canaan is the increase in aspect ratio. “The Cogito wing is [was] about 39ft high, the Alpha wing is 41ft high and Canaan’s wing is 43.5ft high, so we are going taller and narrower. Aspect ratio is always good for reducing induced drag at the top of the wing, so it is a small chord length at the top and we have also pushed the area up higher in the wing. So it is a smaller bottom, because there is a fair bit of loss at the bottom of the wing and it is pretty disturbed air and it is pretty slow air down there too."

While the centre of effort of the Canaan wing is a little higher, its drag is reduced while producing the same amount of lift. The result is that hull flying can happen in even lower wind speed, while the taller rig can also benefit from the potentially stronger winds aloft.

In terms of their slot control and how this has developed Killing says: “It is quite critical how big that is and the time you want the slots to be working really well is when you camber the wing up to maximum to go downwind - you have a 40deg camber on the back of the wing and at that point you want to close up the slot. In the past we have had little fingers that stick out from the front edge of element 3 to hold on to the slot and control it but they weren’t adjustable at all. So we have got rid of the fingers and we now have little control lines that come out to change the size of the slot. You don’t change it actively as you are going up the leg but you would change it at the windward mark and put it on the setting for going downwind - so you can control the slot size.”

For the Canaan wing they have an additional control to adjust twist in the top of the wing. “Normally the twist from the hounds, where the forestay comes in, up to the top of the mast is natural, based on the stiffness of the wing, but now we have a small control up there, so we can keep the camber or flag it off to dump power at the top if we need to.” The downside of this control, says Killing is that it is not self-tacking.

In terms of numbers for the performance improvements between Canaan and Alpha, Killing says that at present they genuinely don’t have them. “We are comfortable that it is faster and it is easier to sail and part of that is the hull shape, but I can’t quantify that.”

Going higher aspect with the rig, typically the performance improvement would be in light conditions, and at present the C-Class does seem to be geared up for this. Killing says that the perfect wind strength is 8-10 knots, as above this you are starting to depower. “The wind speed we would like best is the 10 knots or less range. I think if you ask any C-Class sailor, they’d like that. 15 knots is really exciting and 20 knots - we don’t want to be out there.”

Compared to what we are used to in the big boat world, design development in the C-Class is fairly empirical. Killing says they did some VPP work on the hulls, but the development of the Canaan wing was more a case of them feeling it was right to go higher aspect.

Killing attributes part of the success of their Alpha campaign three years ago down to weight. “We had a crew that was superb sailing in light air, a crew that was lighter than the American team, they were 30lb (13kg) lighter, and the platform was also another 30lb lighter. So it was a powerful product for sailing in the lighter breeze.”

According to Killing the weights of their latest boats are “no lighter”. “Canaan’s wing is higher aspect wing – we haven’t weighed it, but I think it is a little bit heavier because it is taller so it is more difficult to get the structure in. The hull is very similar to our other hulls in construction.”

Typically the platform and the wings are around the same weight 150-170lb (68-77kg) in the wing and about 160-170lb (73-77kg) in the hull. It is a 350lb (158kg) total. “It is about the same weight as the crew. So the crew is 350 and the boat is 350 when you are sailing.”

The following detail shots of Canaan's rig are courtesy of Helena Darvelid of Team Invictus/www.vestassailrocket.com