With the aim of understanding and improving the sea keeping performance of marine craft the research addresses methods of influencing the motions of marine craft by stabilisation mechanisms, and identifying the influences on RIB motions. The two research projects, that attracted industrial support, represent two separate industrial interests concerned with influencing and understanding the influences on the sea keeping performance of marine craft. The first project, focused on developing a motion control system, for motion reduction and/or control of marine structures operating in the free-surface. The aim was to develop a system that would replace, eliminate or complement the use of current devices, in order to improve passenger comfort, overcoming the drawbacks of external hydrodynamic based systems. The research developed a new motion control system and theoretical and physical experimental studies were conducted. The second project, focused on identifying the influence of a RIB tube and the properties of the tube, on the dynamic motions of a RIB, including the effect of the motions on the occupants. Theoretical and experimental studies at full and model scale were conducted.