Previous sailing yachts seakeeping investigation in view of a new set of rules

Abstract

Sailing boat dismasting is an impressive and dangerous event which consequences are obviously critical. The causes that can lead to dismasting just start to be precisely investigated and understood. As a matter of fact, rules of classification societies are nowadays quite poor when it comes to mast and rigging. Indeed, these causes are intricate and of different kinds. One of the reasons of dismasting is the lack of good estimations of the loads that will be applied to the mast and rigging. Part of these loads is due to ship motion in waves, mainly pitching. This work is a study of the pitching behavior of sailing vessels at sea with HydroStar software. It is a potential flow solver using panel methods and developed by Bureau Veritas. Only linear theory is used here. The aim of this paper is to study what are the main parameters that drive a sailing boat pitching behavior. It is a first step in the view of building a simplified method to be able to quickly estimate inertial loads due to waves. First, the global problem of seakeeping and the method used by HydroStar to solve it are briefly presented. Then, pitching motion results in regular waves are shown 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 response amplitude operator is proposed, based only on boat length. Afterwards, method and results about acceleration in the mast are discussed. A very rough but quick formulation to evaluate the longitudinal acceleration or force in the mast is set. A state-of-the-art process is then applied to enlarge results to irregular sea states and compute time series. Good agreement with some real full scale measurements is shown in term of pitching. The sea state parameters influence on pitch motion is studied and the concept of irregular RAO is proposed. The influence of different ship parameters is then studied leading to a short list of key parameters. To finish, a real case scenario is performed using all the previous conclusions on the yacht Kiboko. The aim of these results is to be further compared to on-board measurements that may occur in the next months.