We have developed the robotic vehicle on water that moves by the rider's balance. Previously, due to the lack of stability of the vehicle, balancing skill was required for the rider. In general, the center of buoyancy of the floating body influences on the stability. Therefore, in this paper, the floating vehicle was modeled and the appropriate body shape and size that improves the stability was simulated. We developed the novel vehicle on water named MINAMO (Multidirectional INtuitive Aquatic MObility), which realized higher stability. In addition, in order to improve the maneuverability for the rider, a force plate is introduced as an interface and MINAMO realized the straight and whirl movement by the control of the rider weight shifting.