The high-speed Rigid Hulled Inflatable Boat (RHIB) is one of the key forms of transportation for the U.S. Navy in littoral regions. This planing craft, shown in Figure 1, is a lightweight, high-performance, high-capacity boat. It is constructed with a solid, shaped hull and flexible tubes at the gunwale. The flexible tubes maintain a high buoyancy to avoid capsize in bad seas and to better absorb heavy loads. When the RHIB maneuvers in a seas state greater than 2, however, it often gets off plane or jumps to an entirely different heading regardless of the craft speed and heading relative to the direction of wave propagation. This behavior may cause the planing boat to miss its target track and veer off course. Furthermore, if a RHIB is supporting shore facilities or large ships transporting troops, the deviations and jumps may also impact the safety of the troops. In order to shine a light on improving the RHIB planing craft design for better performance at higher sea states, this study used a fully-nonlinear ship motion model named the Digital Self consistent Ship Experimental Laboratory (DiSSEL) by Lin and Kuang (2011a and 2011b) as a numerical tool to examine the dynamic balance of a six-degree-freedom (6DOF) RHIB. First the RHIB is maneuvered in Seas State 2, then in Seas State 3. The results of the simulation serve to better understand the underlying physics that cause dynamics instability at higher sea states. This study also serves to validate the accuracy of the DiSSEL ship motion model with observational data of a 10-meter long RHIB at Seas State 2. The model shows good agreement with experimental data in all headings and with a wide range of boat speeds (up to Froude number of 1.265).

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