Low - Frequency analysis of super yacht free vibrations

After a long period of crisis and uncertainty the yacht market seems to exit from the tunnel. Many shipyards are developing new interesting projects, especially for vessels over 50 m in length. The high intrinsic value of these vessels fosters technical offices to deepen the research on some critical subjects to increase competitiveness. The onboard comfort, with particular reference to vibrations, is probably one of the key aspects of this trend which nowadays drives most of the design choices relatively to structure lay out and materials for interior outfit. A great help comes from Classification Society new rules and regulations for the evaluation of noise and vibration. The so called "Comfort Class Rules" contain the general criteria for noise and vibration measurements in various yacht areas and suggest maximum limit values as a function of the required quality level of the yacht. In this paper a study carried out in cooperation between the University of Genova and a leading Italian shipyard on the dynamic behaviour of superyacht structures is presented. A detailed FEM analysis of the global and local natural frequencies of a 60 m superyacht was carried out in order to evaluate the reliability of simplified procedures based on reduced numerical models. The investigation has been carried out by two different FEM codes and the numerical results have been compared with experimental data measured during the construction of the vessel.