Creating something big from almost microscopically small parts - North Sails, headquartered in the US state of Nevada, has impressively achieved this feat with its cutting-edge 3Di technology. "The new sails consist of a flexible composite film made from pre-impregnated and spread ultra-thin fibre filament strips, which are applied in multiple axes and formed into a three-dimensional shape under UV radiation," explains the Managing Director of North Sails Germany, Stefan Matschuck.
An excerpt from the sailmakers' reference list shows that the still young invention has already arrived on the maxi scene: "Visione" (45 m, Baltic), "Y3K" (30.50 m, Wally), "Highland Fling" (25.30 m, Goetz Composites) and "Hetairos" (67 m, Baltic) rely on the almost uniform grey laminates, which have a particularly balanced dimensional stability in all load directions due to the precise control over the arrangement and alignment of the material in the sail. "This is why we also call 3Di production 'wing technology'," says Stefan Matschuck. "3Di sails deform so little that the foils provide propulsion almost as stiffly as an aerofoil, even in waves and changing wind conditions."
From 3DL to 3Di. From three-dimensional laminate to three-dimensional interleaved. While the tried-and-tested 3DL foil sails still use continuous yarn threads made of aramid, carbon fibres and UHMWPE (Ultra High Molecular Weight Polyethylene, brand name Spectra/Dyneema) bonded under vacuum and heat as a sandwich in a layer of two Mylar foils, 3Di membranes consist of many thousands of wafer-thin interlaced filament strips. For large maxi yacht sails, up to 400 layers on top of each other are possible.
Sails as stiff as wings
Production and development of the new sail technology takes place exclusively at the state-of-the-art North Sails factory in Nevada. The centrepiece there is a computer-controlled three-dimensional positive mould that can be transformed precisely into the desired 3DL or 3Di profile shape.
A filament strip is a single yarn thread or a filament bundle that has been spread in such a way that the almost microscopically small individual fibre filaments lie side by side, forming a wafer-thin strip that is pre-impregnated with polyester resin and applied to a backing paper.
These rows of filaments, produced in a machine called a "pregger", are then fed into a multi-axis laying machine running on a crane, which is responsible for rolling out the fibre films at the exact angles and positions required. "In order to achieve perfect load distribution in the sail laminate, the North Sails engineers programme the filament strip laying machine, which hovers just above the three-dimensional mould, with the load patterns of the desired sail laminate," explains Stefan Matschuck.
After many thousands of individual prepreg filament strips have found their place on the 3D mould, the curing process, which is also common for other composite structures, takes place under vacuum. Computers control the heat that releases the resin from the pre-impregnated fibres and bonds the individual filament strips together. This turns the many individual elements of a 3Di sail into a solid, integrated structure. And all without the use of carrier membranes.
Martin Hager
Editor in Chief YACHT
