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Caterham Composites Designs Coach Roof for Alex Thomson Racing's IMOCA 60 Yacht

23 October 2012

Caterham Composites was asked by Alex Thomson Racing to bring its expertise to a number of areas of Alex’s IMOCA Open 60.

Alex is the youngest skipper ever to win a round the world race, claiming victory in the 1998/99 Clipper Round the World Race, a record he still holds today. Alex then broke the world distance speed record in 2003 and with his current yacht, he has recently broken the transatlantic solo sailing record, crossing the ocean solo more than 24 hours faster than the previous record.

A key area that Caterham was asked to look at was the development and production of the yacht’s sliding coach roof. The coach roof is designed to offer Alex protection from waves crashing over the deck whilst still allowing him to sail the boat to its full potential. The design of the roof also allows it to slide into a forward position to maximise the cockpit area available for Alex to work in. Caterham explains it had a limited budget, limited material options and the project required completion within a tight timeframe to fit into the overall refit and training schedule. Given the requirements of the project, it used the HyperWorks Suite and the experience of Altair ProductDesign to handle the optimisation of the roof and its composite development capabilities.

Caterham engineers used readily available materials of intermediate modulus carbon fibres in various forms for the outer part of the coach roof. For the core of the product, the engineers used foam and Nomex. The main difference between this and other projects was the production method, led by some time and budget limitations often common in the sailing industry, compared to motor racing. The tooling was made from plywood, which although accurate, cannot resist changes in temperature or pressure. As it could not be autoclaved, the lower volume fraction as well as lower mechanical properties of room temperature curing resin had to be taken into account, all of which was successfully integrated into the project in its final outcome.

One of the primary challenges was to create an item that was light enough not to add excess weight to the yacht’s basic structure, but that would still be able to withstand the huge volumes of water across the deck as the boat powers through the world’s oceans. To meet the expected load requirements, Caterham worked to the ABS and ISO standards for surface pressures and added appropriate safety factors where needed.

Taking all these constraints into account, the engineers started to create the structural design of the yacht’s roof. The materials decided upon were A500 foam and Nomex honeycomb for the core and T800 carbon for the skin. Various forms of woven and UD carbon fibre were used in the analysis and a discrete number of angles were chosen to limit complexity. The cores of the roof were fixed at a thickness of 20 mm. Five load cases were considered in the optimisation process. One load step considers water pressure of 0.65 kNm2 acting on the entire roof while the other four simulate Alex standing on the roof in dynamic situation and in a variety of locations. A two-step optimisation, with a Free Size and a Size Optimisation of the roof followed. In the first step, the free size optimisation, the optimum shape and location of the ply patches are determined, essentially answering the question: Which fibre angles are required where in the structure?

In the following step, size optimisation, Caterham says the optimum thickness for the previously found ply patches were discovered. The engineers optimised the system to reach the following targets:

  • Minimize compliance
  • Constrain mass to 40 kg
  • Constrain deflection to 10 mm
  • Constrain failure index to 0.5