Super Nikka boasts aggressive chines albeit sited relatively high up in order not to prejudice performance upright and in light airs. With relatively conservative and rounded aft sections a single rudder is felt to be more than adequate for good control


minimal negatives in the light-airs upright condition, and was clearly beneficial when heeled over in a breeze.


The balance when drawing hulls of this type is firstly to try to use as much hull length as possible, especially when heeled, without a wetted transom that results in a drag increase, and then to gain as much sta- bility as possible in the powered-up heeled condition upwind and reaching without an imbalanced helm or ending up sticky as a result of too much wetted surface area upright in light airs. Boats just intended for reaching are less troubled by these issues, while boats racing on windward-leeward courses find that balance more difficult, explaining why hard chines aren’t common on inshore designs like TP52s and Mini Maxis. However, with a significant reach- ing component Super Nikka has a wide enough performance profile to make chines an attractive compromise, while retaining the need to perform in light conditions and carry added loads in cruising trim. The North Sails VPP integrates the lift and drag solutions produced by the Das- Boot panel code with other speed-produc- ing factors such as sail area, aero coeffi- cients, stability and so on, to produce the final performance output. Use of panel code allows a wide range of potential solu- tions to be evaluated more quickly thanks


to a simplification of the governing equations (in essence their validity excludes boundary layer effects), but this does have the tendency to over-predict powerful solu- tions like wide transoms and full bows. Validating the final stages of hull shape development using RANS CFD is an inte- gral part of the process. 3D Reynolds Aver- aged Navier Stokes Equations (RANS) yield the most accurate solutions at the cost of a large volume of computation (thou- sands of iterations on multimillion element grids). In return, one can expect a very good assessment of the wave and viscous drag and to catch any drag under-predic- tion from the panel code stages. Using a set-up developed for the KND Volvo 65 RANS program, the appended model featured 10 million elements, evalu- ating drag, rudder angles across the range of heel, and helm balance. Appendage sizing and positioning are a major compo- nent for performance, especially upwind in light airs. In the past it was common for designs of this size to find it difficult to achieve good balance, requiring large amounts of rake to get reasonable rudder angles – which is a key factor in upwind performance. Having resolved this issue during the design of Alegre we were confi- dent regarding predicted balance, even on a relatively wide hull form with a single


rudder and sizable sail plan. The RANS phase confirmed the design was on the right track with smoother stern sections, a relatively high chine aft, and moderate bow sections which produced the most promising combination in our race model. Having originally proposed a relatively large rig for a racer-cruiser, we agreed after discussions with the team and their North sailmaker Alessio Razeto to ensure no compromise was made in terms of per- formance in light conditions, and went back to compare increased rig sizes with their rating impact. One factor in this decision was our experience that VPPs are insensitive to the negative effects of right- ing moment in light conditions. This may partly be down to sailor expectations that heeling early in the light feels faster; but it seems to be backed up by experience racing in the Mediterranean that heeling moment (HM) and righting moment (RM) work best in a certain range. Our revised rig sizing moved the HM/RM relationship towards the better feel end of that band, a step made possible by the powerful hull shape being amenable to the increase in power further up the wind range. Once the hull shape was finalised we prepared preliminary deck shapes to com- bine an effective racer-cruiser deck layout with the aesthetic demands of the client for a sleek, powerful machine, in his words ‘A missile’! At a meeting in Viareggio with Roberto and Alessandro and the other key players in the team this initial idea for a wide, low coachroof with chines and angu- lar cockpit sides to complement the hull shape was refined into the final configura- tion, allowing the boat to be sailed by a range of crew numbers as well as creating a safe, confined space for family sailing. The interior is a development of Roberto’s previous Lady Nikka, similarly finished with minimalist Italian style. It boasts a large, open saloon with galley and desk either side of the main hatch, double guest cabins aft and a large owner’s cabin forwards. Carbon/foam construction incor- porates many techniques and ideas from the practical and resourceful Alessandro Vismara and his team, who have one of Europe’s best track records with stylish performance racer-cruisers, albeit one that perhaps is not so well known outside Italy. Yet again for Mills Design the best projects exhibit a team mentality. The Super Nikka project has been one of the most pleasurable we have undertaken, working with a gifted, enthusiastic owner and a very professional yard as partners. I look forward to enjoying the launching and trials with the team in March 2015, and to working with Vismara Marine on other new projects in the future. Mark Mills, Ireland


q SEAHORSE 47


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