The surf rescue boat (SRB) of the U.S. Coast Guard is a class of high-speed planing boats. This 9-meter craft is capable of operating at speeds up to Froude number 1.7. However, when it begins to maneuver in incident waves near its maximum speed, dynamic instability occurs immediately. In this instance, the craft trims and rolls to a large heel angle with "plow-In," even with small-amplitude incident waves and small course changes. In this study, a fully nonlinear ship motion model named the Digital Self-consistent Ship Experimental Laboratory (DiSSEL) is used as a numerical tool to understand the physics that cause the dynamic instabilities. DiSSEL showed that when SRB reached Froude number 1.698, acceleration resulting from heading change would cause a dynamic force and moment imbalance, resulting in heel and pitch motion instabilities. DiSSEL also showed that if the heading is fixed, and other conditions remain the same, the instability did not occur. Unfortunately, there is no detailed record of the data or numerical simulation of the ship motions in the stable and unstable regions, except for the description of the ship motions by Codega and Lewis (1987). The simulations by DiSSEL agree well with this description.

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