from the transatlantic classics. Signifi- cantly, however, nearly all the Class 40s in the region were originally conceived for crossing oceans; for example, all five of our designs on that side of the Atlantic are classed for Category 0 ocean races. Recognising this, when OCD were contacted by our latest client it was clear from his brief that we should be looking elsewhere ‘within the box’ to produce a design somewhat different from the very high righting moment, high wetted surface, reaching designs that have been developed in the past four years in Europe. Nevertheless, as part of the design process we developed candidate designs of that type, running computer simulations against a series of ever narrower waterline, lower wetted surface alternatives. It’s important to understand that all Class 40s are limited to the same minimum displacement, sail area, maximum stability (measured at 90°), maximum beam and draft. Thus all the main performance dri- ving numbers are a given. Significantly in terms of performance, what remains for the designer to exploit is hull form, appendages and sail plan. Everyone knows that once you change the target events and the result- ing weather environment, the ‘optimal’ boat changes. To take this onboard and thus extract an advantage required some lateral thinking by ourselves, backed by a forward-looking owner and project manager who share an open-minded logi- cal approach to decision making, and are not afraid to stand out from the crowd. At the very first design kick-off meeting the client also made it clear that he was looking to innovate, but add reliability, using where possible US contractors and materials, and to promote the Class 40 in North America. This emphasis on innova- tion while maintaining reliability put some pressure on yard and designers to come up with ways to manage some of our choices since these two requirements obviously don’t always go hand in hand.
Construction
After three weeks in the United States in May, working on the design with the owner, project manager and visiting various yards, finally, Carbon Ocean Yachts were selected as the builders. Clearly almost every owner’s aim when starting such a project is to launch the most competitive Class 40 possible within any limitations set by time and/or budget. Very quickly all parties arrived at the inevitable conclusion that we’d be building in a female tool, not only to save weight in the hull shell but in the hope that it would encourage others to build in the US. Since that initial choice the decision has been taken to go one step further and a female carbon tool has been produced, carbon being a more stable material than glass. This also gave ourselves and the builder the confidence to lower the height of the deck to hull joint down into the vertical panels of the topsides and also to aim for a
40 SEAHORSE
The plug (top) for the female tooling for the new OCD Class 40 (above) illustrates a softer approach to the bow sections reflecting more emphasis on light-air performance
clear-coat topside finish… that judging by the test panels will be absolutely stunning. At the time of writing the 3D files for the deck, cockpit and coachroof have just been released to MouldCam in Bristol RI who are responsible for the five-axis machining of the female deck tool. Prior to this the hull plug had been scanned by laser to confirm its compliance with design tolerances. The manufacture of the hull mould in carbon and the CNC machining of the deck tool provided the builders with the accuracy required to undertake the hull to deck joint in the yacht’s topsides while maintaining that clear finish all over.
Hull
Last month’s Seahorse article Fashionable Logic touched on details of the hull design programme and the weather studies under- taken to target the performance of the hull for the prevailing conditions in northeast America. I won’t dwell further on that but will draw the reader’s attention to the 3D graphics which show some of the results of the latest hull development programme undertaken by OCD in co-operation again with Annapolis-based designer Clay Oliver. While our previous generation of 40s and the majority of later designs carry a hard chine all the way from the bow we have been careful to reduce upright and heeled wetted surface towards the stern by round- ing off the aft sections so that they are more in common with our early first-generation and less powerful designs such as Bolands Mill (2006). This rounded topside to bot- tom section quickly develops in a way that does create a hard chine aft of the yacht’s centre of buoyancy which carries on past
the max waterline beam of the yacht until forward of midships, where the hull form is such that the chine gradually disappears. In the past four years the European ‘Transat-optimised’ 40s have featured a range of bow volumes that by and large have been much greater than 2008/2009- generation boats. These shapes make for a faster reaching boat in medium airs. The resulting hull form produces a chine that (as on our earlier design, 40 Degrees) extends to the bow. With our new boat, although the bow volume is very much greater than on 40 Degrees, we have been careful not to induce excessive upright or heeled wetted surface area in the forward 25 per cent of the yacht. The result is that this new design has, for approximately the same waterline beam, 2m2
less upright and
heeled wetted surface area than an Atlantic-optimised boat, for very little reduction in righting moment. In effect, the hull form in the middle of the boat contin- ues to develop the form stability for good upwind and reaching performance while we shed wetted surface area towards the bow and stern to improve performance at lower speeds and angles of heel. Weather studies for the Bermuda races and for the east coast of the US between Charleston and Newport around the timing of the Atlantic Cup for the past 12 years provide the clues as to why the final design headed in this direction…
Bermuda races: % of distance sailed in true wind speed of 10kt or less = 41% % of distance sailed in true wind speed of 16kt or more = 29%
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