Composites analysis

Case Study

Design of carbon fibre mast, turret and boom components for a new yacht rig

Carbonworks was approached by one of its clients to design and supervise the construction of carbon fibre yacht mast, turret and boom components for a fast-cruising 49 foot (15 metre) catamaran being built on the Gold Coast in Australia. To help optimise the design of the rig, linear buckling analysis, composite analysis, material testing and static stress analysis was carried out using LUSAS Composite.

The rig differs from conventional rigs in that it is a free-standing mast and "swing-rig" with an unusual headboard, which has been called the "turret". The turret enables larger sails to be fitted to produce more power. Being an unusual rig there was much debate on defining the design loadcases. Carbonworks developed several draft loadcases and commissioned two other companies to do the same. These loadcases were developed using non-linear rig models from specialist sources. Over a period of two months this information was compiled and compared until a final design loadcase was settled upon. The critical loads were determined to be ultimate mast compression and forestay catenary tension. Ultimate load was developed at 40 knots apparent and full sail of 120 square metres. Ultimate load is intended to be when the mast breaks. This represents a mast compression in the order of 25 tonnes and a distributed load down the 20m mast of 2N/mm. The turret transmits the full compression load from the rigging to the mast, and is consequently very highly stressed.

Parallel to this work, draft material specifications were developed from information provided by the material suppliers and the preferred fabricators. The mast was made as a pressure moulded component and the turret is to be made as a shrink-wrapped consolidated, wound mandrel piece. Draft material specifications were used to produce preliminary mast and turret models. The turret had a target weight of 60kg. The draft turret model showed this was feasible, so the turret design was developed further resulting in a 57kg component. The LUSAS Composite modeller proved to be very capable in allowing changes in specifications and geometry to be implemented rapidly. Some designs were imported from Autocad and Cadkey drafting packages using the IGES translation and import facility. Tsai-Wu and Tsai-Wu-Cowin theories were used to determine First Ply Failure situations. Linear buckling analysis was used to ensure that mast and turret buckled at a load factor of 1.2 or greater.


The turret is 6m long, approximately 230mm in diameter, and made from prepreg carbon fibre. The turret was modelled in LUSAS Composite using semiloof thin shell elements and consisted of laminates with 7 to 22 layers. The turret has several holes for halyards and control lines in areas of maximum compression. LUSAS Composite was used to determine if these holes contributed to premature buckling, and to assess how much unidirectional carbon fibre was needed each side of the holes to act as a bypass for the loadpath. In addition, the attachment points to the mast are slender webs and LUSAS Composite helped determine their minimum thickness to prevent buckling. The design cycle consisted of building a very thin model of about half the target weight, based upon hand calculations. Linear buckling analysis was done to determine where it would fail. The failed area was thickened, then run again, usually moving the buckle to somewhere else. When the model was failing at about a load factor of one, a stress analysis was done to check the stress regime. Some areas had to be reinforced due to overloading, either by ply orientation changes or using more sublaminates in patches.

Solarrig turret assembly

LUSAS model of boom showing first mode of failure
Turret modelling Boom modelling
Tsai-Wu stress in selected ply around holes for halyards in underside of turret
 Tsai-Wu stress in selected ply around holes for halyards in underside of turret

Tsai-Wu-Cowin failure plot of turret central rib

Carbon-fibre turret - typical composite failure results plot
Tsai-Wu failure plot for turret tacking track rail
Carbon-fibre turret - typical composite failure results plot

When the component designs were complete and agreed to by the Client, Fabricator, and the Designer, material samples were made and tested to verify the draft material specifications. A couple of surprises were found with low laminate modulus and low tensile strengths. LUSAS Composite was also used to carry-out simulated tensile and compressive tests in parallel with the physical tests. The laminate failure criteria was then tuned to the physical tests, a safety factor added and the draft models re-analysed and modified to accommodate the changed material specifications. Changes were not too dramatic and again LUSAS Composite allowed easy modification of the models. After a review of the models and checking up to date information, final drawings and laminate schedules were released and the mast was built.

The project provided an opportunity to complete a design using the linear buckling, composite analysis, material testing and static stress analysis capabilities of LUSAS Composite.  

"With the associative modelling capabilities of the LUSAS Composite modeller, design changes were easily incorporated into the finite element models. This resulted in rig components that were designed to the client's specification, had a high reliability, and were optimised for the imposed loadings".

Peter Schwarzel, Carbonworks


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