Reliability analysis of crabbing manoeuvre

In this study reliability analysis methods are applied to the crabbing manoeuvre of a ship. The objective is to express the crabbing capability of a ship in terms of probability of failure, rather than a simple yes/no verification which does not take into account any uncertainties in the mathematical model. To this purpose three reliability methods are presented and applied to the case of a ship sustaining a transverse wind force. These methods are the First Order-Second Moment, the First Order Reliability Method with Rosenblatt transformation and a Monte Carlo simulation. A more complex case, with longitudinal, transverse and rotational equilibrium requirements, is also assessed with Monte Carlo simulations. With these reliability methods it is possible to overcome some limitations of static crabbing calculations, such as assuming a constant wind and using conservative empirical coefficients for safety. Moreover, deriving the crabbing capability in this way provides more information than a standard crabbing analysis thanks to the estimation of the probability of failure.