Sea trial of prototype Vertical Weight Stabilizer (VWS) anti-rolling system for small ships

Abstract

Anti-rolling is an important technique for safety and efficient ship operation. In the era of sailing ships, rolling motions were not so severe compared to those of modern ships running by prime mover without sails, because the sail itself had a damping effect on rolling motion. After propeller driven ships exceeded sailing ships in number and performance, namely, from the end of the nineteenth century, many types of anti-rolling–related techniques were invented and developed, of both passive and active types. Recently (2009, 2010), as sea trials, we carried out proto-type experiments on an anti-rolling system and confirmed its effectiveness. The new concept utilizes the so-called Corioli’s effect, which appears in the rotational coordinate system. Usually, this effect is considered as virtual, but the real effect appears when a mass moves in the radial direction in a rotating coordinate system. In the case of ship rolling, the vertical motion of a mass generates Corioli’s force to finally generate anti-rolling moment. This is the reason the system was named Vertical Weight Stabilizer (VWS). This new system was invented in 1998 by Hirayama, and confirmed by the model experiments in a towing tank. Numerical simulations were carried out by the Sea and Air Control System laboratory of Yokohama National University, but the actual system could not be realized, because we could not find an appropriate actuator. The key technology for the success of the current sea experiment is the powerful, high-speed, compact actuator for the vertical movement of the weight. In this paper, we introduce this new concept by adopting a simple experiment, the control system with new actuator used in an actual sea experiment, and report on the successful results.