Feature 4 | COMPOSITE CONSTRUCTION
the-world race shows that hard-learned lessons in terms of composite structures have been taken on board. A sign of the rapid technological
evolution taking place in grand prix yacht racing is the fact that skipper Alex Tomson’s second Hugo Boss is some 25% lighter than his previous Open 60 of the same name, which was unfortunately lost in the Southern Ocean as a result of keel failure during last year’s Velux 5 Oceans Race. Tis weight reduction was achieved despite a significant increase in loadings, up to 20% in some cases. ‘Tese latest Open 60s are a lot more
powerful than the previous genera- tion,’ says Paolo Manganelli, one of the engineers with SP (the marine business of Gurit) that was responsible for the craſt’s structural engineering. ‘Tere’s hardly a design load in the latest Hugo Boss that is not substantially greater than the previous generation.’ Improved materials, for instance lighter
sandwich cores, helped reduce the overall weight while SP was able to optimise the structure on the basis of better knowledge of loads experienced in ocean-going events and improved structural analysis. Te structure was modelled using finite element analysis and other tools, and utilising load measurements made on Tomson’s previous Hugo Boss. Declares Manganelli, ‘By the time we
get to design the next generation, we’ll probably be able to go further. With every race we move forward our collaboration with the yacht designers and have access to new and better structured materials.’ Precise details of performance craft
laminates are hard to come by in the early stages, but it is believed that top-grade materials specified for the vessel hull and deck structure included high-elongation unidirectional carbon for the carbon- epoxy skins, together with a core of Kevlar honeycomb plus Nomex aramid and Corecell styrene acrylo-nitrile (SAN) structural foams, the SAN being used for areas of the forward hull that are most subject to high slamming loads. Several different densities of hexagonal and over-expanded honeycomb core were used. High-modulus carbon was employed for the keel fin, twin rudders, and mast. UK-based boat builder Neville Hutton
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A V24 racing powerboat (courtesy Jory/Raymarine).
used female moulds to produce the boat and this, with scrupulous care from the build team, resulted in an exemplary finish, the 18m structure requiring a minimum of fairing and finishing aſter demoulding. Mould shells were of carbon in vinyl-ester resin held in shape by wooden backing frames. Major items were cured in ovens for up to 16 hours at temperatures of 70°C-80°C. Watertight structural bulkheads were fabricated on a laminating table with carbon/epoxy skins over honeycomb core. Reinforcing stringers and beams were moulded into the hull and deck to augment strength and rigidity. Most of these are cored, though a few are monolithic.
Powered performance Te high strength-to-weight properties of reinforced plastics are also key to a wide range of high-performance powered craſt, including racing powerboats. It is hard to imagine some of the shapes of these craſt being produced in anything but mouldable plastics, while orientating the reinforcing fibres along load paths provides the ability to tailor strength and stiffness precisely where they are needed. A useful example is the V24 powerboat
designed by Ocke Mannerfelt, who also designed its Batboat predecessor. Tese craſt are distinguished by the wing-like appendages at deck level that contribute
some lift and account for the bat comparison. (At speeds of up to 80knots, these boats could also be referred to as ‘bats out of hell’!) Mannerfelt is one of the designers who
helped drive the move away from the traditional chined, flattish hull form once used to achieve planing speeds to the now ubiquitous ‘V’ hull having fore and aſt running strakes for directional stability. Te V24 has a V hull bottom that is
also stepped in two places to minimise wetted area as the boat rises in the water at speed and to help aerate the water’s surface layer, so providing a more forgiv- ing ride. Te hull rounds off to a convex deck, the resulting compressed circular form providing high hoop strength. V24 was intended for enthusiasts of
average means so limits for price and minimum weight were pitched to rule out ‘exotics’ like carbon fibre/epoxy while allowing a level of structural integrity consistent with repeatedly racing at top speed across choppy water and the occasional ‘stuff’ into a wave. Sandwich construction was specified above the waterline and solid laminate beneath. Te transom and area towards the stern had to be strong enough to withstand the propulsive force, torque, and vibration of an affordable 320hp engine, either outboard or inboard with outdrive unit. Builder of the first dozen boats, Mark Pascoe Ltd of Swanwick, UK, used an
Ship & Boat International May/June 2008
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