Surface roughness of fibre reinforced composite sails as quality indicator for their appropriate use

Abstract

Knowing that maximum sail performance or usage can be achieved with an optimal aerodynamic shape of the sails, stability of the initial sail shape, its air impermeability and smooth surface, sailmakers thought that their search for the ideal sailcloth is finished when laminated sails were first introduced in the early 1970s. These sails were made as fibre-reinforced composites (FRC) and had all properties in one: light weight, high strength, low stretch and smooth surface. Although FRC sails revolutionised sail-making and sailing generally, today, after almost 50 years of research and development in the field, the search for a perfect sailcloth, especially in the racing or high demanding sailing, is not finished. One of the sailcloth quality parameters that was not yet been investigated thoroughly and fully understood is sailcloth's surface smoothness/roughness. This is why we started investigating surface roughness of the most often used FRC sailcloth. By using the modified Kawabata evaluation system (KES) measurements, we manage to determine differences in surface roughness and friction coefficient for the face and the back side of the investigated FRC sailcloth. The results obtained could explain why some high-performance and highly sophisticated sailcloths are not appropriate for winning a race.