60ft trimaran technology - pt2

Today we look at wingmast that cant and can their rake changed

This article follows on from our interview with Sergio Tacchini's Damian Foxall and yesterday's look at appendage technology in the 60ft trimaran class

Sails

The sail wardrobes on the 60ft trimarans are all fairly similar maintains Antoine Mermod, who handed the technical side of Karine Fauconnier's Sergio Tacchini 60ft trimaran campaign. A majority of sails are built in 3DL or D4 if they are made by the popular French loft Incidences, otherwise Cuben fibre is used. Unusually laminates sails are not used for their potential weight benefits.

"They are not so much lighter than panel sails, but they have a very good shape and it keeps it for a very long time," says Mermod. "So in comparison with a Kevlar sail it is the same weight. I'm sure they will try to make them lighter, but the problem is to keep a good shape for a long time and not to break the sail. Under our rules we can have 15 sails over two years. So we can have three mains, three Solent jibs, three trinquettes, three gennikers three RORC (storm jib) and so we have to make a good choice for that. We use Cuben fibre for the genniker because it is very light which is good for short handed racing and it is waterproof which is better if it is on the deck. And sometimes we use Cuben for the little jib for the same reason - it is always on deck and very light, but for the mainsail, trinquette, solent, we use Kevlar or carbon 3DL or D4."

Masts

The powerhouse behind the 60ft trimarans are the towering rotating wingmasts. Sailing with this equipment is quite a unique experience says Damian Foxall. "It is not like a dinghy rig where you are trying to bend the rig or reduce sail shape, it is fundamentally an aerodynamic thing and you just want to split the average apparent wind. When I say average - low down the apparent wind is further forward and as you get up towards the masthead apparent wind is further back. If you are upwind maybe you want to privilege more the apparent wind at the bottom because it will affect the slot quite a bit or if you are downwind you maybe want to be closer to the apparent wind at the top of the mast because the slot is bigger. But basically you are only talking about a 2-3 degree difference and fundamentally you just want to split the apparent wind." On Sergio Tacchini normally the apparent wind angle is about 24degs off the bow upwind and 40degrees when sailing 'downwind'.

Thanks to the use of giant hydraulic rams attached to the bottom of the shrouds they can also cant the entire rig to weather. On Sergio Tacchini the rig can be canted by +/- 9degs. Other boats in the fleet can cant theirs by as much as 12degrees. "Generally you are trying to maintain the maximum projected area," explains Foxall. "You want it to be perpendicular to the horizon. In light airs, maybe there is something to be said for having that little bit of windsurfer effect and you have it kicked a little bit to weather and it lifts a little bit but I find it hard to believe that in this type of class where the boats are so heavy that this lift is going to have any real effect. I think it is more to do with helm balance and maximum projected sail area. Canting the mast is shifting the centre of effort laterally and certainly when the wind gets light that is crucial. It does two things - it shifts the centre of effort to leeward and gives more feel to the helm. It also shifts the weight to leeward as well."



Foncia showing off how much her rig can be canted

Generally when the boat is fully powered up, the mast is fully canted to weather and it is slowly dropped to leeward or at least to 0deg as the wind dies. "So as wind dies you are sailing with less heel. Also to keep the leeward hull in the water and keep the weather one out moving the weight of the rig becomes quite important."

Aside from being able to cant the entire rig to weather they can also rake it fore and aft by around +/- 4degs. "We have found that it is a useful tool, but probably not as earth shattering as you would expect, maybe it is because at the moment we don’t have as much in as we would like. I think it is a bit under-utilised for us - we need to work on that a bit more. Fundamentally you are moving the centre of effort fore and aft - upwind and downwind - or depending upon your different rig configurations. So if you are going from full reef and solent to one reef and solent then theoretically you’d want to drop the rig back to keep the boat balanced. Generally we have it forward upwind and forward downwind at the moment. Reaching or in heavier airs we drop it back a bit."

Most of the boats have removable inner forestays that are tensioned on hydraulics and Foxall says it is pretty vital to remember the state of these when trimming the rig fore and aft. "Normally you have the inner forestay in place, so you don’t want to be easing the rig back and forgetting to release that as it wouldn’t be too healthy for the rig..."



Mast and boat breakage

Over the last three years the 60ft trimaran class have seen a ridiculous number of wingmasts come tumbling down. Mermod thinks that no one reason is to blame.

"When you design the mast you have three things: first you have the theoretical load you take. I think the theoretical load was too low because of carbon mainsails and the stiffness of the new boats and also because they are now racing in grand prix with full crew and good teams and hard racing - so the maximum load was higher than people thought.

"The second thing is that when you calculate the loads in the mast you have a mathematical model which simulates the boat through numerical equations. This model was not so good for this new situation - the new way of sailing the boats and especially for the sail combinations we use. So we always test the boat with full main and genniker, but we don’t think about for example what it will be like with staysail and full main, and so we reached the limit with the mathematical model.



"The third thing was the materials and the characteristics of the materials that we had - between the theoretical numbers and reality there is a big difference. Also we have built 20 masts in perhaps the last two years, before it was maybe one mast every two years. And the problem is that we need a lot of carbon for the hull - not only for the mast but for the hulls too - and I think perhaps we didn’t have the best materials because the army or Boeing get that. Then afterwards the quality of the material is proportion to the ability of the guy working with it - we always want masts quickly and we want a lot of masts, so the companies who build them need extra guys and they don’t get taught very well. The last thing is that the teams want to have a lot of system like hook, so we put a lot of things on the masts and sometimes there have been mistakes..."

Mermod says that although they build in a safety co-efficient of two when calculating the structure of the rigs with all these possible imperfections and variables this co-efficent is not enough. He adds "And all the reasons of all the dismastings were different. There are titanium padeye which broke on TIM, so it was a mistake of the crew because we know never to put a titanium padeye in this place. Groupama dismasted because the mast broke and we don’t know why, so all the reasons are different."

One effect of the carnage in last year's Route du Rhum was that the class opened up a lot and there has been an exchange of information, particularly about the structures of the boats, between designers and engineers. Several points were identified - in particular that Nomex honeycomb as a sandwich material creates too brittle a laminate, as does high modulus carbon fibre. As a result the class have limited the modulus of the carbon fibre to M46. "It is much more reliable and the co-efficient of security is much bigger," says Mermod.

The principle reason for the float breakages on the Irens tris last year was that compared to the older generation boats the giant rams used to cant the rig were moved from the deck of the floats to the rear face of the aft crossbeams and so what was thought to be superfluous structure was removed from the floats. Mermod thinks that the Nomex core and its ability to accept a regular thrashing from breaking waves was to blame.

Thus in areas such as the fairings for the crossbeams and the floats that are subject to constant wave impacts, foam is now the core material of choice over Nomex. Also in these areas considerably more internal structure has been added to the boats in the form of stringers, frames and bulkheads. "The idea is that if we had a panel then we divide it into three or parts with a frame or a bulkhead - every designer has got different ideas, but the general idea was to have small areas which were unsupported."

The problem of hulls fracturing has not been limited to the Irens design. A month prior to the start of the Transat Jacques Vabre the van Peteghem-Prevost designed Belgacom experienced a similar problem (albeit not as catastrophic) which is also though to have been a failure of the Nomex.

So what next for the 60ft trimarans? Despite winning the Transat Jacques Vabre Franck Cammas has a new 60ft trimaran nearing completion and there is rumour that Baron Rothschild may be ordering a new Gitana. In the meantime the class is holding it breath awaiting the arrival of Yves Parlier's new 60ft twin rigged catamaran - the first two hulled craft in the class for more than a decade, which if it is successful could send the designers back to the drawing board...