Numerical and Experimental Study of a Sailing Yacht Assisted by the Use of Strain Gauges
This study has been carried out within a framework of research activities regarding the innovative design and manufacturing of a small sailing yacht (called LED - Linen Epoxy Dinghy). These activities have been performed at the Dipartimento di Ingegneria Chimica, Gestionale, Informatica e Meccanica of the University of Palermo, in cooperation with the Facoltà di Ingegneria e Architettura of the University of Enna Kore. The purpose was to evaluate the strain field of a 15' SKIFF type sailing yacht by using strain gauges, and compare the experimental evaluation with the prediction of a Finite Element Method (FEM) model.
Due to the application of the load system, FEM results obtained from preliminary numerical simulations identified the most critical deformed areas, located in the hull (fig.1), and in transversal and longitudinal internal stiffeners (fig.2). The hull material is in particular a sandwich structure composed by Flax Reinforced Plastic skin laminates and by agglomerated cork as core. Strain components were measured on the internal skin of the hull, by means of four three-grid rosettes HBM type RY81-6/350, and a thermal compensator rosette. The sites of maximum normal strains on the transversal and longitudinal stiffeners of the yacht (made of marine plywood), were also considered, by installing four single-grid HBM strain gauges, type LY11-6/350 and a thermal compensator strain gauge.
Each single grid in all installations was wired up by using a four wires scheme, and protected with polyurethane paint from HBM type PU140 and a silicone sealing layer from HBM type SG250 (fig.3 and 4).
A load configuration was reproduced in the lab, simulating a loading scenario acting on the boat during typical sailing conditions (fig.5).
The measurement of strain gauge signals was carried out using Wheatstone bridges. The acquired signals, sampled over a time window sufficient to achieve a stabilized behavior, were then processed to obtain the complete strain state and to compare it with equivalent numerical FEM results.
The matching of experimental and numerical results was very satisfactory, allowing to conclude that the FEM model is reliable. Moreover, the confidence gained about the reliability of the measured data, has opened the way for an experimental campaign of on-site measurements, during real sailing conditions. This procedure will require the connection of a strain gauge controller with a transponder and a GPS system.