Why Carbon?

Carbon Meets a Classic

A 42 metre traditional sailing yacht has been fitted with four advanced carbon fibre spars – and all that expertise is hidden under timber cladding

Formula Yacht Spars is one of the UK’s leading companies in carbon fibre technology and one of the premier suppliers of carbon yacht spars for the racing, cruising and superyacht market worldwide. Since it acquired Hood Yacht Spars a few years ago it has increased its capacity and resource base, enabling it to cater for all the different sectors of the market, including superyachts and unusual custom builds.

The company is constantly working on the latest design optimisation of mast laminates and their associated components. The parameters for the mast design analysis require the input of all the boat details to ascertain the stresses and inertias to which the spar will be subjected. Masts, booms and spinnaker poles are engineered using the relevant in-house software to obtain a complete picture of the rig and its stress-load design. Formula Yacht Spars’ engineers use computer-aided design (CAD), Catia V5 and 3D Solidworks software to design and engineer the perfectly customised rig package, while Finite Element Analysis (FEA) is used to validate the complex engineering requirements.

In an unusual recent commission, the company was asked to build four lightweight carbon spars for a 42 metre classic yacht. Carbon fibre was specified as it is currently the most efficient material for mast manufacture. It is considerably lighter than aluminium but has ten times the tensile strength.
The yacht had to keep the appearance of a traditionally rigged vessel, so the spars were timber clad for a more authentic appearance. The company project-managed the entire rig, sourcing the deck gear, furling systems and even the sails.

Formula employs one of two methods of manufacture, using either a male or female moulding with aerospace-quality pre-impregnated carbon fibres that cure at temperatures between 90 and 120 degrees Celsius.

Experts determine the optimum resin content to ensure complete saturation of the fibres, thus preventing dry spots and ensuring that the design weight of the mast is adhered to accurately.

All carbon laminates are debulked during production to reduce air and voids in the lay-up, and autoclave pressures of up to six bars are applied during the curing process.

Where required, extra layers of doubling are applied in the manufacturing process to strengthen high load areas such as the mast step, gooseneck, vang fittings, spreaders, hounds and the masthead. A precise schedule is followed and the masts are engineered to use the requisite modulus of carbon, combining a range of different section shapes with the correct laminate stack to create an almost infinite number of performance characteristics.

For the classic yacht, staff employed the male moulding technique by which continuous structural fibres connect major and secondary load paths to ensure a high-strength integral laminate. The seamless laminate is formed on the rotational male mandrel where the tow is laid accurately at angles ranging from 6 to 88 degrees. As fibre orientation is the deciding factor in the overall strength of a carbon spar, the co-ordination of the different axes of motion that create the various filament winding angles is critical. For this reason the winding is controlled and monitored by custom design software in the CNC winding machine to create an extremely precise composite structure. Because of the thickness of the laminate both of the main spars were vacuum-bagged as well as stretch-taped.

The wooden cladding was applied by specialist craftsmen experienced in both wood and composites, the veneer being glued to the carbon spar using epoxy adhesive and sealed using a clear epoxy resin. It is finished with a UV-stable polyurethane varnish, and all high-load areas will be leathered in the traditional fashion. Throughout the build the Formula team has worked hand-in-hand with the boatbuilders in a two-way transfer of specialist knowledge, to ensure that the final product has the cosmetic finish of a classic rig.

As with many of the custom rigs Formula builds, it will also be supplying the running rigging and deck gear package, including Lewmar hydraulic winches and furlers and Spinlock high-spec clutches. Sails for the project have been made by UK sailmaker Banks Sails, which has experience in this specialist area and has worked closely with Formula to ensure authenticity.

Mark Merritt, group managing director of Formula Yacht Spars, says: ‘This is an unusual project for us as it blends modern carbon technology developed from our America’s Cup and Volvo Ocean Race customers with traditional boatbuilding craftsmanship. The result has been a lightweight set of spars that look exactly like their traditional counterparts. I am extremely proud of our teams’ commitment to the task and it will be exceptionally rewarding when we see the vessel hoist her sails.’

This article first appeared in Boat International, Issue 255, September 2007
Reproduced by kind permission