Abstract
In this study, the mechanism of a transverse stability loss at super high forward speed is investigated. Towing tank test is carried out to observe the characteristics of the instability and it is confirmed that the instability has strong relationship to the change in running attitude and hydrodynamic roll moment due to high forward speed. Using some existing empirical formulas to estimate the dynamic normal force (lift) on a planing surface, an estimation method of inception of the unstable phenomenon is proposed and its validity is confirmed through comparing with measured results.