The assessment of a ship capsizing risk in beam sea is one of the most important indicators for measuring a vessel's basic performance. The authors have proposed a method to qualitatively and quantitatively calculate the response and capsizing probability of systems with nonlinearities in roll damping and restoring moment. For example, it is difficult to accurately measure roll damping, one of the parameters governing ship motion, on a real ship. Therefore, it must be estimated by Bayesian inference from time series data, for example. In such cases, the estimated parameters are distributed stochastically and never have definite values. As a result, the response distribution and capsizing risk would also be further stochastically distributed. This is a probability distribution of a probability distribution, which is known as a second-order distribution. In this study, we propose a calculation method to theoretically obtain the second-order distribution of capsizing probability.

To reduce GHG and fuelcosts, we introduce a new wind propulsion device called a “Windmillsail” that combines the characteristics of a rotor sail and a vertical axis wind turbine based on the concept of a “rotor sail that rotates with the force of the wind”. The shape of the windmill sail is designed to be rotationally symmetrical in order to ensure that they always move forward regardless of the wind direction. Inaddition, in order to maximize magnus force, the shape of the sail has multiple parallel wings. It has greater propulsive force than rigid-wingsails, and unlike rotorsails, it can generate electricity while propelling. The 2-D hydrodynamic analysis confirmed that the lift coefficient exceeds 5 and at the same time the power coefficient is about 0.25. This paper outlines the characteristics of windmill sails, their development to date, and a vision for the future.