Nautor was the first company to adopt SPRINT technology in the production of a large structure and this was first applied in the manufacture of the Swan 45. The lightweight decks on this full bred racer cruiser provided practical production experience for SP and allowed the SPRINT range to be refined to increase robustness, flexibility in fabric and resin selection.

The production process also initiated the introduction of tack films for work on vertical surfaces. In turn, Nautor's commitment to the project has seen the company make considerable investment in new production facilities, including a 100ft computer-controlled curing oven that facilitates precise temperature control throughout the curing process.

On completion, the Swan 45 performed beautifully and consistently achieved good results on the race course.

Nautor was obviously keen to capitalise on the successful performance of this first SPRINT production boat and the concept of the Nautor 601 was born. The design house of German Frers and the engineering expertise of the SP structural engineering team was called upon with the aim of producing a superior performance yacht, normally only associated with custom one-off builds, yet produced as a series production boat.

From a production perspective, the vessel had to be uncomplicated to construct without compromising the values Nautor customers expect - superior quality of interior comfort and stylish fit-out, all combined with impressive racing performance.

This brief called for the use of state-of-the-art materials and innovative manufacturing processes, combined with an intelligent approach to engineering. SP was confident it could deliver.

Production processing With the one-design concept, every aspect of the build of the boat must be repeatable.

SPRINT, with its fixed resin content, fibre weights and precatalysed resin systems, means accurate weight and laminate thickness can be produced consistently in a simple process with the opportunity for error removed.

A prototype was not produced for the Swan 601 project, so each boat in the series, including the first, had to be exact and delivered at the correct weight with no margin for error as future modifications could not be made.

The Swan 601 hulls were produced in split female moulds. The majority of the hull's skins consisted of three layers of SPRINT with an extra layer of unidirectional carbon prepreg in certain areas for extra stiffness.

The outer skin was laid first, followed by the fitting of Core Cell® P Foam in the topsides and S-Core in the hull bottom, forward of the keel and below waterline. S-Core, or SPRINTCore, is a unique moulding material that can be used to quickly increase laminate thickness whilst maintaining excellent mechanical properties.

S-core consists of a single layer of a polyester non-woven material with a pressure stable honeycomb structure, applied to a pre-cast, pre-catalysed resin film. The product is highly drapable, making it fast and easy to fit in areas of high curvature, such as in the bow of a yacht. The resulting laminate is very durable and strong, yet lightweight and economical to produce. S-core is also used in areas of the deck for additional stiffness and strength.

Using a team of eight men, the inner skin of the 601 was then laid. This whole process took only three and a half days before applying the vacuum bag and curing - an extremely rapid laminating time by ordinary standards.

Core bonding The inclusion of extra resin within the SPRINT material to facilitate core bonding resulted in further time savings in what would normally be a very time consuming process of priming the core, or the use of glue films, either side of the core material. Not only was the procedure extremely time efficient, it was also very clean, completely eradicating the need for any wet systems and the associated drawbacks.

Good standards and continuous improvement of Health & Safety practices are a very important issue for Nautor which strives to improve the environment for its operators.

All the internal structure - bulkheads, transverse, longitudinal beams, keel box and engine mounting structure - were produced separately in female moulds.

The Swan 601's bulkheads and internal frames are constructed with flanges so they can be sited and bonded into place with high strength structural adhesives - again minimising wet laminating processes and reducing man hours and labour costs considerably. On the recommendation of SP's technical team the structure was bonded into the hull using a combination of SP's Spabond 345, 340LV and 130 adhesives.

Working with SPRINT and female moulds also means the laminate thickness is extremely predictable and repeatable.

This, combined with a consistent surface finish, allows certain tolerances to be achieved, enabling the secondary bonding of the internal structure to be a relatively simple process. The need to compensate for miscalculations that can result in the filling of large gaps or cutting of laminates is also removed.

"Once we became familiar with the process, SPRINT has proven to be a reliable, predictable material, " commented Kjell Vesto, Nautor's technical director. "At the same time as saving valuable man hours, it also enables you to accurately predict final weights and properties of laminates which makes boatbuilding easier."

We are able to repeatedly produce laminates with very low void contents, correct fibre to resin ratios and predict mechanical properties - exactly what a reputable boat builder needs, he added.

At the time of this publication going to print, three Swan 601s have successfully undergone sea trials and are now attracting a good deal of attention on the water.