A simplified method for the evaluation of inertial loads on sailing yachts

The aim of this work was to improve the understanding of dismasting, in view of the development of a new set of Rig Certification Rules specifically aimed at sailing yacht design, In the first phase of this project a preliminary systematic analysis of the dismastings of a large set of boats of different type and size has been carried out. By examining all these events, typical collapse modes have been identified, showing that whereas the traditional approach to mast scantlings is based on static loads, many of the failures took place as a result of severe dynamic loads. For this reason attention has been focused on the dynamic loads acting on the rigging caused by the response of the sailing yacht to waves. Especially in the case of boats with large displacement, these loads could be of a greater magnitude than static ones, and their evaluation must be earned out through seakeeping analysis. In particular pitching motions are extremely important, since they can cause severe accelerations to mast and rigging, possibly leading to mast collapse. Indeed dismasting is a significant event, very dangerous for the crew and very expensive to be repaired. In this paper a systematic study of the pitching behaviour of a database of sailing yachts was carried out. Using these results a simplified formulation is given to quickly evaluate the longitudinal acceleration at the mast centre of gravity. A state-of-the-art process is then used to obtain results in irregular sea states and to compute time series. Despite the small size of the database, this could be regarded as a first step towards the formulation of a simplified method based only on the boat length; this method would be able rapidly to estimate inertial loads due to waves.