A Simplified Method to Assess Acceleration Loads on Sailing Yacht Masts.

The behavior of sailing boats in open sea is related not only to their hydrodynamic performances but also to the dynamic loads acting on the hull and rigging. Especially in case of large vessels these loads cannot be neglected and their evaluation could be done just by a careful seakeeping analysis. Particular attention should be devoted to the acceleration loads caused by pitching motions which can create severe problems to mast and rigging, with extreme consequence represented by the mast collapse. As a matter of fact dismasting can be an impressive event, very dangerous for crew and very expensive to be repaired. Apart from the human error, one of the main reason of dismasting is represented by the lack of estimation of loads that could be applied to mast and rigging by the dynamic behavior of the vessel at sea. In addition Classification Societies' Rules are quite poor about this subject and the mast and rigging design is normally in the hands of designers. The aim of this work is to investigate in deep the causes which can cause dismasting and to propose possible actions to avoid it. With this goal in mind a study of the pitching behavior of a number of different sailing yachts has been carried out by the well known HydroStar software: it is a potential flow solver using panel methods and developed by Bureau Veritas. The investigation was aimed at studying the main parameters that drive sailing boat pitching behavior. This could be considered a first step in view of the formulation of a simplified method, able to quickly estimate inertial loads due to waves. Pitching motions in regular waves are calculated and analyzed for a small set of modern sailing yachts hulls. Despite the small size of the database a first simple method to estimate pitch RAO is proposed, based only on the boat length. From the pitch knowledge a very rough and quick formulation to evaluate the longitudinal acceleration in the mast centre of gravity has been carried out. A state-of-the-art process is then used in order to achieve results in irregular sea states and compute time series. Good agreement with some full scale measurements is shown in term of pitching.