In this paper the scantling procedures contained in the “Design and Construction of Pleasure Boats” Rules of the Italian Classification Society RINA, relatively to GRP vessels, are assessed in detail. This work represents the continuation of a joint research performed in cooperation by AZIMUT Shipyards in Avigliana (Italy) and the Dipartimento di Ingegneria Navale of the University of Genova. Scantling procedures contained in Classification Societies Rules are based mainly on minimum requirement formulas, corrected by semi-empirical coefficients and safety factors, which take into account possible uncertainties about material behavior, stiffener sections and geometric imperfections. In order to check the efficiency of these safety factors, a specific study has been started up within the joint research. In the first phase of the investigation a statistical analysis of dimensional and geometric characteristics of a number of medium size motor yachts have been performed, aiming at expressing the main scantling formulas as a function of minimum number of variables. In the second phase several versions of the same part of a 55’ motor yacht, chosen as reference vessel, have been obtained by parametrically varying the main scantling variables In the third phase, for each of the obtained structures, the correspondent finite element model has been created by the FEM code NASTRAN. Finally the safety factors of RINA scantling formulas have been evaluated by studying the stress levels of all models and comparing them with the RINA equivalent stress level.
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