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Kokomo III: 3,000 Square Meters of Doyle Stratis

Doyle Sailmakers will be delivering the latest 58.4-meter Kokomo with the largest Stratis sails to date. The new Alloy Yacht designed by Dubois Naval Architects is fitted with the world’s 2nd biggest carbon fiber mast at 75 meters tall. Doyle Sails New Zealand is fitting Kokomo with 3,000 square meters of Stratis sails.

Doyle Sailmakers have become one of the leading manufacturers of superyachts sails with 4 of the 5 finalists in this year’s Superyacht awards sporting Doyle STRATIS™ sails. Doyle Sails head designer Richard Bouzaid explains the process for developing a STRATIS™ sail for a Superyacht, from the sail design and fit to the boat, through the engineering and manufacture of the STRATIS™ membrane at the 21,000 square foot temperature and humidity controlled plant in Auckland New Zealand.

As with any sail, the first stage in the process is the sizing of the sail. This is especially important on large yachts as errors are costly and often require cranes or the like to take sails on and off a yacht. Accurate measurements are required of all the parameters of the boat to ensure that this process is done correctly. Our first stage in the process is to build an accurate 3D model of the yacht within our design software. These models are accurate to millimeters and include all of the relevant detailing that can effect the fit and performance of the sail. The model shown below is the new 58 meter Dubois designed Kokomo.

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These models include all details of the sail attachment points, furling units, head swivels, mast detail with halyard positions, spreaders and other potential conflicts with the sail such as communication equipment, genoa cars in potential positions, stanchions etc. This allows us to then fit a sail to the model and know with certainty that the sail will not only fit correctly to the 3 attachment points, namely head, tack and clew, but also where and if the sail will have other stress or chafe points due to fittings on the boat. They can then be suitably reinforced or the geometry altered to avoid this conflict. The accuracy of this type of modeling has been one of the biggest steps forward with sail design software in the last 10 years.

Shape optimization is the next stage in the sail design process. Base sail shape molds are used for certain geometries and applications and then adjusted for the requirements of the actual sail that is being designed, for example a cruising genoa will have more shape in the back to be more effective when the sheet is eased. During this process the sails will be accurately aligned to the actual attachment points so that mastbend and headstay sags can be incorporated into the sail design. Loadpath (custom fiber laid sails) as a sail is engineered to stretch a certain amount, rather than to a % of its ultimate breaking strength. For a high performing sail we would be typically looking for a maximum elongation anywhere in the membrane in the region of 0.15-0.2% and it is important that the elongation (stretch) is as uniform as possible in the membrane in all areas of use. This dictates how much fiber is required in any area of the sail. The graphic shows the stretch through the sail and where the sail has more stretch than the desired amount, shown green.

During this process of establishing the correct fiber alignment and density, different combination of fibers may be used to get the best balance between weight and overall durability. There are various fibers that we use in a STRATIS™ sail depending on the application. Performance cruising boats will typically use Vectran or a combination between Vectran and carbon fiber. Performance racing boats will use twaron (Kevlar), Carbon fiber or a combination of twaron and Carbon fiber.

Once the orientation of the fibers and the density has been finalized the fiber map for the sail will be programmed into the 12m wide x-y plotters that will lay these fibers onto the surface that will become one of the sides of the finished sail. These fibers are all laid under tension to exact paths determined by the earlier studies.

The final process in the membrane manufacture is the application of the top surface.This is also a film sheet, often with a polyester taffeta on the outside, and pre coated with glue. This is finally vacuum bagged to the table and the laminator, which uses infrared heat lamps and 12000KG of downward pressure. The laminator will then make computer controlled passes over the membrane to activate the glue and expel and remaining air in the laminate. The factory has 2 of this style of laminator operating. The membrane is left to cure for several days before being moved to the Doyle New Zealand 30,000 square foot sail loft floor for finishing, or shipping to one of the many Doyle Lofts worldwide for completion.

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