This paper presents an advanced and accurate integrated system for the design and performance optimization of fiber reinforced sails -commonly named string sails- developed by SMAR Azure Ltd. This integrated design system allows sail designers not only to design sail-shapes and the reinforcing fiber paths, but also to validate the performance of the flying sail-shape and have accurate production details including the overall sail weight, material used, which means costs, and length of the fiber paths, which means production time. The SMAR Azure design and analysis method includes a validated and computationally efficient structural analysis method coupled with a modified vortex lattice method, with wake relaxation, to enable a proper aero-elastic simulation of sails in upwind conditions. The structural analysis method takes into account the geometric non-linearity and wrinkling behavior of membrane structures –such as sails-, the fiber layout, the influence of battens, trimming loads and interaction with rigging elements, e.g. luff sag calculation on a headstay, in a timely manner. This method has been extensively validated and used to optimize several racing and super-yachts sailing plans. Specifically, this paper presents a validated optimization of a real fiber reinforce membrane sail plan of 140’, 240 ton aluminium Super Yacht, carried out in collaboration with Paolo Semeraro (from Banks Sails Europe), who designs and produces the MEMBRANE™ and BFAST™ string sails, the latter with Marco Semeraro. Both BFAST and Bank Sails have been using the SMAR Azure technology for almost a decade and notwithstanding the long experience of Mr. Semeraro in using the technology, given the sailplan-size and detailed customer requirements, among which improved durability, strength and reliability and smooth use of in-boom furling, this project was carried out incooperation with the SMAR Azure technical team. A total of 1000 sqm of upwind sailing area was analyzed and optimized. A combination of Dyneema TM Sk 90 and black Twaron 2200 was chosen for the fibers and a triple step lamination under hi-pressure plus laminated patches utilizing the same fibers where added to prevent local deformation of the corners. A long term vacuumed post-curing period sealed the production phases. The final sail plan is -as anticipated by the analysis results- holds the desired shape and is stronger. The final fiber layout shows a reduction in maximum stress by 22% compared to the initial design; this was achieved with only 11% (4kg) gain in fiber weight.

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