Advanced technologies move into the fast cruising market – and at affordable prices

Today at Vismara we are steadily transferring into all our new yachts – racing and cruising – the same technologies developed during more than 30 years of in-house research and development. From regatta racers to fast cruisers, our research is now particularly focused on delivering to cruising sailors the same great strides in performance that have been seen in recent years in the best racing fleets.

We are now offering a wholly new philosophy in the fast cruising sector, maximising a yacht’s abilities in everything from everyday life onboard to performance on the race circuit. This is what we are calling our prêt-a-porter approach… from a shipyard that since 1984 has successfully launched more than 150 custom yachts.

International design team
In Vismara we used to talk about the Open Company, meaning working with as many leading external experts as possible along with close co-operation with the customer. Our latest models were developed by a multinational team led by Alessandro Vismara.

Mark Mills Yacht Design has put immense effort into optimising the naval architecture of both the new Vismara 62 SuperNikka and the forthcoming Vismara 56 (above). Working alongside the Spanish specialists at KND Sailing Performance, Mills made extensive use of Computational Fluid Dynamics (CFD) while Hernan Salerno took the lead with the structural calculations (something he has done for many years at Vismara). Last but not least, Lucio Micheletti, who previously worked for both ourselves and the Italian shipyard Solaris, is now in charge of developing the interior design of the Vismara 56 along with other new custom projects.

Open co-operation with the best people in their field and continuous innovation are at the heart of our day-to-day work experience.

Engineering structures
There is no such thing as best design without innovation, and innovation is a risk if there aren’t the solid technical foundations already in place. The aim at Vismara Marine Spa is to engineer all the structures of our yachts in-house to give maximum confidence to the end-user.

Easy handling is ultimately what our clients look for when they come to Vismara. Enjoying the sailing experience is what we would like to ensure for all our customers, and this is possible only by employing good engineering, both in terms of structures and handling systems.

To achieve this Vismara recently invested heavily in engineering and design tools to support the launch of two more prêt-a-porter designs: the Vismara V62 and Vismara V50. The first Vismara V50 launches in July and hull number 2 will launch before the end of this year. Shortly afterwards, Vismara V62 hull number 1 – a fast cruising creation all in advanced composite materials that is descended from the custom SuperNikka – will launch at the beginning of 2016.

SuperNikka is an aggressive 62ft IRC racer-cruiser that showcases the performance solutions developed by Vismara: a carbon high-performance dual-purpose design with an efficient lifting keel, plus removable bow thruster and dinghy stowage door allowing her to change modes quickly and easily.

All of our lightweight carbon fast cruising yachts incorporate the lightest possible integrated furniture, again created in-house. As Alessandro Vismara, founder and now CEO of Vismara Marine, likes to say: ‘Each object onboard has to serve at least three purposes, that’s the only way to control the added weight of the necessary comfort features on luxurious but fast boats such as those that we offer our customers.’
Michele Antonini

Vismara 56 Mills Design summary

Introduction
This report describes the design process used to develop the Vismara 56 Mills hull, appendages and sail plan, including a brief description of the tools (CFD & VPP) used to investigate the hull shape performance.
This has involved the following tasks:

• Set-up of the evaluation loop (CFD & VPP)

• Design and testing of hull shapes

• Evaluation of sail plan

Design outline
The Vismara 56 Mills performance cruising design has been prepared for a well-known Italian owner, to conform to a number of requirements based on his experience with previous boats. The brief described a high-performance cruising boat, capable of being sailed shorthanded or with non-sailing family and friends, with comfortable interior and exterior spaces. The boat would be likely to daysail off Sardinia as well as make longer passages around the Mediterranean. Particular emphasis was laid on performance in higher wind strengths, with a desire to avoid reefing below 20kt and to rely on furling headsails of various sizes to cover the full range of wind speeds.

The extensive interior accommodation developed by Vismara Marine with Lucio Micheletti inevitably occupied a significant percentage of the weight tally, reducing the VCG available for the stable upwind sailing in higher winds desired by the client. To compensate for this and to provide the interior volume desired it was clear that a beamy hull shape was required, with a wide beam waterline to produce the form stability necessary to match a reasonable sail plan.

Candidate evaluation: tools and methods
Hull shapes are assessed using the North Sails VPP, taking in drag data from the Das Boot panel code CFD solver and aero coefficients from the KND library appropriate for a design of this type. These lift and drag inputs are then output as predicted boat speeds across a matrix of wind speeds and angles. The matrix we used weights the four wind angles equally, reflecting the allaround use envisaged for the design: VMG beating, 80° reaching, 120° reaching and VMG running.

CFD
A major component of the R&D programme is the generation of hydro coefficients which the VPP will use to predict the candidate hull shape performance. CFD is now considered the most efficient way of generating these hydro coefficients as it is possible to evaluate a large number of candidates in a limited amount of time and it is not bound by the scaling issues tied to tank testing. Two types of CFD were used in this program:

• Panel Code evaluations, thanks to a simplification of the governing equations (in essence their validity excludes turbulent flows), are able to deliver a solution in a matter of minutes. This allows a wide range of potential solutions to be evaluated quickly. The panel code used is the Das Boot code developed by Michael Richelson, used in conjunction with his North Sails VPP that integrates the lift and drag solutions from Das Boot with the other speed producing factors such as sail area, coefficients, stability etc to produce the final performance output. The Panel Code CFD uses the double rudders developed for this design.
•  3D Reynolds Averaged Navier Stokes Equations (RANSE) yield the most accurate solutions at the cost of a large volume of computation (thousands of iterations on million elements grids). In return, one can expect a high-quality assessment of the wave and viscous drag. A new use of RANS in waves has been developed by KND, the Vismara 56 being the second project it has been used on (the original single rudder solution was used for RANS wave modelling to simplify the meshing).

Both solutions must be combined to ensure efficiency and accuracy of the prediction. All candidate hull shapes were evaluated using CFD Panel Code to maximise resources in investigating a wide range of possibilities, while RANS CFD was used to refine the solutions on the final candidate hull to avoid serious pitfalls – for example, panel code is prone to over-predict the performance of powerful solutions such as chine height and stem fullness.

Development of hull shapes
Within the starting parameters of a target length of 17m, target weight in lightship trim initially of 14,800kg (revised after discussions with Vismara to 14,000kg (the weight being saved with the use of an integrated furniture system and carefully minimised cable runs) and the max draft of 2.80m, an initial hull shape was developed to start the process based on the final SuperNikka hull. 112 was a chined-shape drawing from Open Class design where reaching is prioritised with a wide hull shape, mediumheight chines and a reasonably wide waterline beam to produce a stable all-round performer.

Various iterations were tried such as altered Prismatic Coefficient Cp and LCB, narrower beam, more powerful stern and bow shapes, higher and lower chines to identify a hull shape that could perform well across the wind range. As progress was made the improved shapes became the basis of the next iteration to combine the positive attributes. Toward the end of the process a reduction in the target displacement was made to improve performance and reduction in waterline length to reduce fears of transom immersion in light airs, and finally an aftward adjustment to LCB was made to allow the hull to trim correctly based on the preliminary weight study.

The final candidate 130 (above) shows the evolution towards fuller sections forwards, lower chine height (approx 120mm) adding stability when heeled, as well as the raised freeboard to match the Vismara Marine model.
Mark Mills

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