Castorama B&Q technology

In part one of this article we look at developments that were made during her engineering and construction

Allowing readers of thedailysail a small respite from reading about Ellen MacArthur's new Castorama B&Q trimaran, over the next couple of days we look at some of the more technical aspects of the boat including a new sheet release mechanism Ellen hopes to be using and Offshore Challenges' state of the art integrated comms and video conferencing package.

But first off, there is another aspect of Castorama B&Q that represents a more fundamental development over what has gone before - namely her build and engineering.

Engineering

The big tri was designed by Nigel Irens and Benoit Cabaret, both based in France while back on this side of the Channel in the New Forest, John Levell performed the immense engineering study of the boat. In doing this Levell obviously turned for reference to the vessel's nearest equivalent - the ORMA 60ft trimarans, in particular the most recent of Irens' designs.

"The main drive was to make it safe and to try and evolve where Nigel has been on the 60 tris," says John Levell whose backgroud is as an engineer for the aerospace industry. Among numerous jobs he has carried structural work for Airbus, satellites for British Aerospace and a composite float plane.

"The funny thing was that the first month I never even looked at the new boat. I was looking at the strength and pressure loads that three of the old 60s Nigel had designed could withstand and then trying to extrapolate from that in order to come up with our best guess of what sort of loads the new tri would need to be designed for," says Levell.

Levell says that with Castorama B&Q they were attempting to increase the safety factor of the boat by 50% proportionally to a 60ft tri. "Which isn’t very much," he adds. "It depends upon what you think the 60s are designed to. Considering they have just broken you might consider that they have been designed to 1!"

Of concern to all the design team was the structural problems the ORMA 60s had experienced in the 2002 Route du Rhum in particular the core failures in their state of the art carbon/Nomex construction.

With the new tri Levell was keen to prevent any repeat of these catastrophic failures particularly as Castorama B&Q is destined to set out on a round the world record attempt and must tackle the Southern Ocean. "One of the things that was very apparent from say Fuji’s problems [ click here to listen to Loick Peyron's audio account of exactly what is was like on board when her float broke and the mast came down] was that it was strong, but it wasn’t tough," points out Levell. "So as soon as you had an initial failure it was going to run very quickly and become critical. Whereas the idea with this boat is that we have used Airex a lot underwater and we’ve kept the panels quite small and we’ve put quite a lot of skin links in. So when we get damage, which we will get - we have tried to make sure it won’t run." More on this later.

Aside from the floats being of a much much larger cross section that a 60ft tri's, there are also around 68 watertight bulkheads throughout the boat. In comparison an ORMA 60 has around 10-15.

The overall structure of the boat is no stiffer proportionally than a 60ft trimaran, but when it comes to wave impact resistance, the trimaran should be much more robust. "We have gone for structures which are more 45degree-based and are less stiff so that they should attenuate the peaks of the loads - in theory," continues Levell. "But there ain’t a book on this. The whole philosophy is like going from the 60s, evolving, trying to come up with extra safety factor and trying to look back at Nigel’s experience of what has survived in terms of materials such as Airex and saying ‘we’ve got this, ok let’s move forward here and we think this is a really good stab’."

Due to the large amount of development work that went into the boat Levell only carried out a basic finite element analysis of the boat. "We did the whole boat, but only as a stick model. So we have got five tubes - two beams, three hulls - and we used it to work out the relative interactions of torsional and bending moments between each of the five tubes. Once you have got torque in one end it has to come out of the other end, so it was a matter of finding out what those shares are and where the major redundancies in the structure were."



Some of the loads are quite impressive - the main sheet is 9 tonnes, and the ball on which the rotating mast sits is expected to see 56.5 tonnes - roughly eight London doubledecker buses parked on top of it. Of particular concern have been the appendages and their potential vulnerability. For example the daggerboard is designed to take a 'thwhap' of 16 tonnes on its side while around it is perhaps one of the most substantial crash boxes we have seen.

The daggerboard is naturally racked aft by 30 degrees so most objects will simply slide beneath the board. In the event of a collision with something more substantial the daggerboard case is packed with foam forward at the top and on its rear at the bottom. Levell thinks this should allow the board to hinge back by a further 5 degrees during a severe impact. In the event that the board does somehow break, it is double ended and can be inverted.

While the main hull rudder has a kick-up system in the event of a collision, the spade rudders don't have this. However Levell has engineered them to break in a certain way. "We have notched them beneath the bottom bearing to create a weak spot so that if they hit something at 30 odd knots that we don’t end up with a stock broken half way through between the bearings - that would be a nightmare," he says. The rudders are fitted with bearings that will allow Ellen to drop out the old rudder and pop in a new one while at sea.



Peter and Sari Ullrich

The build

Integral to the Offshore Challenges cunning plan for Castorama B&Q was building in the southern hemisphere. Not only was there a cost implication in this, but it also would enable Ellen to repeat the shakedown cruise back to Europe as proved so useful following the launch of her Open 60 in 2000.

Boatspeed was eventually chosen after recommendation from designer Hugh Welbourn who had worked with Peter and Sari Ullrich's yard during the build of the maxi Bols.

If Castorama B&Q has been built for record breaking then it is fair to say she has already set one record already. Located in a new facility 80km outside of Sydney, Boatspeed managed to complete the construction of this highly complex 75ft trimaran in just seven months.

Peter Ullrich says that before this project they had positively shied away from building multihulls. Now they love it. "We have always looked at these things and wondered how they build them - now we know! It was a real challenge. It was like building a super-big 18ft skiff. It was nice to get back into the ‘how the hell are you going to do this’ caper. They are so radically different to monohulls."



The detailed work that John Levell put into the engineering, while ensuring the safest possible construction for the boat, also made for a hugely complex build. Not only were there the huge number of bulkheads to fit, but to prevent core failure the boat is a complete jigsaw of different core materials - almost every type available on the market was used somewhere in the boat.

Everything was built in carbon fibre, but due to Irens' recent experience in the 60ft trimaran class they have only used state of the art Nomex core in some areas such as the deck of the main hull. In areas where the hull is likely to experience wave impact Airex is used (in the bottom of the floats and the decks of the floats) while balsa was the core in the chines in the floats. Around some deck fitting high density Corecell was used.

"We have certainly optimised every area of the core. We’ve never used so many different materials in a boat before, but with justifiable reason for every one of them," says Ullrich. "They have all gone down at different times and the main hull has at least 12 separate component panels with full skin links."

The skin links - a small wall of carbon joining the inner and outer skins - were fitted so that if should the hull experience core shear it's spread would be limited. "That of course adds to the time, but because we had so many cores we still had to have multiple hits anyway. I think the main hull had at least six core pulls on it. Normally we cycle the oven four times in the course of a monohull build. With this we cycled the oven 12 times - that is a lot of cure cycles."

The main hull of Castorama B&Q was built over a male mould, while the beams and floats came off female moulds as both floats and crossbeams are identical in shape (although the structure in them is different). Lamination was carried out using BoatSpeed's own CustomPreg technique (read more about this here).

With the build happening in Australia, the design coming out of France and the engineering out of the UK much emailling went on. In fact the time difference worked to their advantage - as BoatSpeed closed for the day they would present a number of problems to the design and engineering team and would normally find a solution in their inbox when they arrived for work the next morning.

A huge advantage to the proceedings is that Nigel Irens is also a boatbuilder with considerable experience of building 60ft trimrans. Over the years he has developed his own terminology and techniques, that took Ullrich quite a while to learn. "We have learned a fair number of new terms from trimaran circles. We have been using things like band aids which we hadn’t been aware of in the past. Band aids and shims were in the beam laminate. We’ve even got drawings with liquorice allsorts on them and spaghetti laminates and broomsticks. You feel a bit ignorant and have to ask him what he means..."



An aspect which Ullrich said he hadn't fully apreciated was how much space a 75ft trimaran in construction takes up. "We weren’t aware that these boats tend to be built by a number of different yards doing different components. So that was a real issue. This thing takes up as much space as three 100 footers to build because they have so many component parts."

For Ullrich this was the first time he has been really impressed by building a boat directly using lofting created in a 3D modelling package. "It was brilliantly lofted by Benoit in Nigel’s office. All of the cut lines were scribed into our moulds and all the trim lines and the beam-float intersections before we started building the boat and we cut every one of those on the line and those all fitted perfectly. That was really impressive and we got to the point where we just totally trusted them."



The proof of the pudding came when they finally trucked the boat to Sydney and set it up in a shed at the water's edge. "The floats had datum lines so we set everything up to a laser and you were able to hang those in space at the right height and amazingly the bottom of the bilges on the floats were within 3mm of being accurate off the plans and that was after all the moulding processes and working from a set of establish datums. So the thing is awesomely accurate and that is all due to the level of accuracy of the drawings."

In total Ullrich says more than 30,000 manhours went into the construction of the boat with upwards of 30 staff working on it. Some of the tooling particularly for the floats and part of the beam moulding was carried out on a five axis mill in Queensland and shipped down while the moulds for the float were built nearby at Griffin Motor Yachts due to space and time constraints. The last major parts to be built were the beams and during their construction Boat Speed staff worked in shifts around the clock.

Mid-November and the parts were ready to be shipped down to Sydney where they assembled the boat in just three weeks. "It wasn’t until much later that they told us they normally take three months to put together!" says Ullrich.

Tomorrow we will look at the new sheet release mechanism planned for the boat and Offshore Challenges state of the art on board video conferencing