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While the biggest international sail lofts continue to invest in the development of ever more sophisticated proprietary sail and rig design tools the range of open access applications is also expanding steadily...


For sailmakers to continue to innovate and improve sail performance they must have a means of assessing the impact of numerous small design changes. This task is consider- ably complicated by the fact that the sail’s flying shape is the result of the aeroelastic behaviour of the sail structure under the influence of aerodynamic loading. Tradi- tionally sailmakers have used a process of trial and error prototyping in which a sail is made and tested on the water. Quantitative performance gains are


hard to characterise like this due to the vagaries of the testing conditions and diffi- culty in measuring the sail-generated forces. Numerical approaches promise to


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overcome these limitations by giving an unparalleled picture of both the aero - dynamic flow fields and the structural response of the sails and rigs due to the aerodynamic forces. Recent developments by K-Epsilon and


BSG Development, among others, have made such advanced fluid-structure inter- action (FSI) analysis more widely access - ible to the many sailmakers around the world who lack the substantial resources required to create such tools in-house.


Tools and sails The sail design software SailPack developed by BSG has now been in use for a long time in numerous sail lofts. It is a sophisticated tool that allows a sail designer to develop and analyse sails of nearly any form imagin- able and then construct them. To model the rig SailPack can include


nearly any type of equipment thanks to a large library of basic elements (rams, pistons, beams, cables) which gives a very realistic and interactive rig model, even for unconventional configurations. The same approach is applied to the sails


for which all types of films, fibres, fabrics, reinforcements and battens are modelled. The designer can opt to develop the sail


shape considering the rig and its initial dock tuning; the programme offers a precise visu- alisation of the structure under loads and allows you to then modify the sail and rig settings which will of course give a new sail- ing configuration – similar to full-scale test- ing on the water. At each calculation loop it is possible to change the sail trim, structure of the sails and all the mechanical character- istics of the rigging and immediately visu- alise the effect on the state of stresses and deformations of the rig and sails. But just because such tools are becoming


more widely available, do not under - estimate the sophistication of the processes required. To solve the sail aeroelastic prob- lem both structure and fluid must be con- sidered. The structure of a sail is compli- cated and interacts with that of the rig, such that a numerical approach is necessary. K-Struct, a finite element structural


solver developed by K-Epsilon, considers the composite structure of the sail and the structure of the complete rig. Detailed


JEAN-MARIE LIOT/DPPI


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